Memoirs of a Computer Pioneer (Mit Press Series in the History of Computing) 0262231220, 9780262231220

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noirs. of a Computer Pioneer

Wilkes

$19.95

Memoirs of a Computer Pioneer by Maurice Wilkes Maurice Willces was one of the leading sci­ entific explorers in the development of the ' modern digital computer. He directed the Mathematical Laboratory (later named the Computer Laboratory) at Cambridge Uni­ versity,. where he and his team built the EDSAC, the first stored-program digital corhputer to go into service. Wilkes describes in nontechnical detail the growth of EDSAC and its successor, EDSAC 2, his introduction of micropro­ gramming, and the first experiments with time-sharing systems. In the 1950s, when machines were still getting larger rather than smaller, Wilkes was one of the few who foresaw a time when nonspecialists would be using computers almost univer­ sally, and he reviews his anticipatory ef­ forts to develop simple programming sys­ tems. But his book is more than a history of computing; it also recounts the allied scientific effort when he was one of those scientists and engineers ("boffins" as they were called by the RAF) who were in the thick of it, his electronics skills enlisted in the new and exciting development of radar. In this absorbing autobiography, Wilkes is as concerned with people and places as he is with computer components and pro­ gams of development. He deftly sketches his childhood in the English midlands and his student days at Cambridge, where he studied mathematical physics and his boy­ hood fascination with radio matured. He conveys the excitement of sudden insights

and long-sought breakthroughs against life's simpler pleasures and trials. His account brims with assessments and anec­ dotes of such contemporaries as Turing, Hartree, von Neumann, Aiken, and a dozen others—and with his impressions of America and Germany formed during his scientific journeys. Maurice Wilkes retired from his post at Cambridge University in 1980, when he becfame a Senior Consulting Engineer at Digital Equipment Corporation in Massa­ chusetts and Adjunct Professor at MIT. Memoirs of a Computer Pioneer is included in the History of Computing series, edited by I. Bernard Cohen and William Aspray. •

Memoirs o f a Computer Pioneer

M IT P ress Series in th e H is to ry o f C o m p u tin g

I. Bernard Cohen, editor; William Aspray, associate editor Editorial Board: Bernard Galler, University of Michigan, Ann Arbor, Michigan; J. A. N. Lee, Virginia Polytechnic Institute, Blacksburg, Virginia; Arthur Norberg, Charles Babbage Institute, Minneapolis, Minnesota; Brian Randell, University of Newcastle, Newcastle upon Tyne; Henry Tropp, Humboldt State College, Areata, California; Heinz Zemanek, Vienna, Austria Memories That Shaped an Industry, Emerson W. Pugh, 1984 The Computer Comes of Age, R. Moreau, 1984 Memoirs of a Computer Pioneer, Maurice V. Wilkes, 1985

Memoirs o f a Computer Pioneer

by M aurice

\ Wilkes

The MIT Press Cambridge, Massachusetts London, England

© 1985 by T he M assachusetts Institute o f Technology

All rights reserved. No part of this book may be reproduced in any form by any electronic or mechanical means (including photocopying, recording, or information storage and retrieval) without permission in writing from the publisher. This book was set in Baskerville by The MIT Press Computergraphics Department, using magnetic tapes supplied by the author, and printed and bound by Halliday Lithograph in the United States of America.

Library of Congress Cataloging in Publication Data Wilkes, M. V. (Maurice Vincent) Memoirs of a computer pioneer. (MIT Press series in the history of computing) Bibliography: p. Includes index. 1. Computers—History. 2. Wilkes, M. V. (Maurice Vincent) 3. Engineers—Great Britain—Biography. I. Title. II. Series. 001.64'09 QA76.17.W55 1985 85-6667 ISBN 0-262-23122-0

Contents

Series Foreword

vii

1 Shooldays

1

2 Undergraduate years

9

3 Post-graduate research

20

4 War

31

5 Experience on radar sites

40

6 Air Defence Experimental Establishment

7 Operational research

64

8 TRE

81

9 A trip to Germany

90

54

vi

Contents

10 Post-war reconstruction

103

11 Atmospheric oscillations

111

12 The Moore School

116

13 The EDSAC

127

14 First steps in programming

143

15 Germany revisited

154

16 Computer progress in the United States

160

17 EDSAC 2

184

18 Can machines think and other topics

19 Computer progress 1955—80

Sources and acknowledgements Index

233

208

231

195

Series Foreword

Maurice V. Wilkes is known to the computer world for his pioneering breakthrough in constructing the first machine to go into service that was designed to embody the new concept of the stored program. This machine, EDSAC (Electronic Delay Storage Automatic Calculator), was constructed in the Mathematical Laboratory (later known as the Com­ puter Laboratory) of Cambridge University. It performed its first cal­ culation on 6 May 1949 and was in continuous use until 1958. Most critical historians of the computer do not consider any machine to be a “computer” unless it embodies the stored-program concept; the EDSAC is by this criterion the first fully operational computer. Ac­ cording to a statement made by Wilkes, the EDSAC “was designed according to the principles expounded by J. Presper Eckert, Jr., John W. Mauchly, and others at the summer school held in 1946 at the Moore School of Electrical Engineering” of the University of Penn­ sylvania, which Wilkes was “privileged to attend.” The EDSAC was the inspiration for one of the earliest commercial computers, the LEO, completed in 1951 by the Lyons Company, whose computer operations today form part of ICL. Wilkes had in mind three objectives from the beginning: (1) to show that a binary stored-program computer could be constructed and operated, (2) to make a start with a development of programming techniques, even then seen by him to be a subject of more than trivial content, and (3) to apply the techniques developed in a variety of application fields. Wilkes succeeded better than any other early pioneer in his second objective. According to his colleague Stanley Gill, Wilkes “led the first practical development of programming for stored-program machines including the first program library” of subroutines. The new programming techniques were described in a book published in 1951, by Wilkes, Gill, and David Wheeler, which served as the basic primer on the subject for more than a decade in Britain and the United States.1 Another area in which he was an important pioneer was a

viii

Series Foreword

specific technique “to provide a systematic approach and an orderly approach to designing the control section of any computer system.” We are told that in this context, “the term ‘control’ is taken to mean the interpretation and execution of a machine instruction.” Wilkes is also known for later developments in machine-independent computing. In this connection he developed an elementary language for list­ processing known as WISP. He also contributed to the development and use of time-sharing systems. Fellow of the Royal Society (1956), Wilkes was the first president of the British Computer Society (1957-1960) and the first member from the United Kingdom of the Council of IFIP (1960—1963). He gave the ACM Turing Lecture in 1967 and received the AFIPS Harry Goode Award in 1968. Elected a Foreign Associate of the U.S. National Acad­ emy of Engineering in 1977, he was elected three years later to the U.S. National Academy of Sciences. After a distinguished career at Cambridge University Wilkes came to the United States in 1980 and joined Digital Equipment Corporation as a senior consulting engineer. Wilkes’s autobiography spans the early years of the development of the computer. It is a work of particular interest, furthermore, because it relates Wilkes’s experience during World War II as a “boffin,” that is, a scientist in military service. It is difficult to think of any other account that portrays this activity with the vivid qualities of the present book. This aspect is of significance, for, as Wilkes exemplifies and as others have observed, many of the early pioneers in the computer field drew heavily on their experience of electronics in wartime service. This book is part of a series devoted to the history of computers and data processing. Other volumes have dealt with, or will deal with, various aspects of the development of systems, hardware, and software, encompassing both general works and specialized monographs. Some of these may concentrate on a particular development, such as magnetic memory, or the technical history of an industrial company. This is the first work in the series of an autobiographical nature. It is certainly to be hoped that other pioneers will make their experiences available to us and that we will be able to publish additional critical and bio­ graphical accounts of those who have made the modem computer. I. Bernard Cohen, Editor William Aspray, Associate Editor1 1. See Maurice V. Wilkes, David J. Wheeler, and Stanley Gill, The Preparation o f Programs fo r an Electronic Digital Computer, with special reference to the EDSAC a n d the use o f a library o f subroutines

(Cambridge, Massachusetts: Addison-Wesley Press, Inc., 1951; reprinted by Tomash Publishers and The MIT Press, 1982).

Memoirs o f a Computer Pioneer

1 Schooldays

A small girl ran up the garden path eager to share the good news— “There’s peace”. The date was 11 November 1918 and I was 5 years and 4 months old. Earlier that day—so it seems, but more likely it was some time later—I had attended my father as he fixed in position a flagpole bearing a Union Jack. Up and down the street, other flags were similarly displayed. Great occasions make strong impressions and, although these scenes are not the earliest I can recall from my early childhood, they are the most vivid. The flagpole projected from our bathroom window and I could to this day describe exactly how the cords securing it were anchored to the floor. I was, of course, too young to know what the war had meant, but I remember the blackout and the tension in the home when my father was late returning. The streets were as dark as in the Second World War and the best thing one could do was to walk alongside a horse-drawn dray or other vehicle and take advantage of its flickering oil lamps. At the time of the Armistice, I had not yet started school. I did so the next year in good time to enjoy the treat provided in honour of the signing of the Peace Treaty. There were games and other rejoicings and an exciting paper bag which, on investigation, was found to contain eatables. The rejoicings and the eatables are all in the past, but I still have the Peace Medal with a red, white, and blue ribbon that I was given to wear that day. I did not learn much at the small private school to which I had been sent and I had quite a lot of time at home on account of illness. I was afflicted with bouts of asthma, an alarming circumstance, since my mother suffered severely from this complaint which had struck her in early adult life. In my case, it was allergic in origin and soon cleared up; I associate with it the acute hay fever from which I suffered

2

Memoirs o f a Computer Pioneer

later in life, but which I am glad to say I have now grown out of. It was my mother’s asthma that caused my father to give up the house in Dudley where I had been bom and take one in Stourbridge. This made his own life very much harder, as he continued to work in Dudley. During the war years, and for many years afterwards, he would walk every morning to Stourbridge Junction station where he would catch the train for Dudley. He arrived home in the evening at 6 o’clock and since, while I was still small, his arrival was also the signal for me to go to bed, I did not see much of him. Later, when motor transport became generally available, this area in the north of Worcestershire was ideal for living in, since its amenides were effectively protected by a series of geological faults that brought the South Staf­ fordshire coalfield to an abrupt end. My father worked for the Earl of Dudley who owned an extensive estate in South Staffordshire. Many years before, a far-sighted pro­ gramme, which included the building of a standard gauge railway, had been set on foot to develop the mineral resources of this estate. At about the turn of the century, in order further to improve com­ munications, a small private telephone system had been installed. My father’s first job was to work the telephone switchboard which was situated just off the entrance hall of a building known as “The Priory” and used partly for offices and partly as the residence of Sir Gilbert Claughton, Lord Dudley’s cousin and chief mineral agent. Telephone switchboards were still something of a novelty and Sir Gilbert would frequently bring visitors to see it, so that in this way my father came under his eye. My father was nothing if not ambitious and after a time sought promotion. This was granted and he became a junior clerk. One of his duties was to pay—in gold coin—the wages at various collieries and other undertakings on the estate, and for this purpose he would be driven out in a pony-trap by a young coachman, by name Joe Brown. My mother was fond of telling how, when still at Dudley, she dressed me in my best and wheeled me out in my pram to meet my father on his return from one of these expeditions, but how he sailed by in his smart equipage without seeing her and thus reduced her to tears. The head of my father’s office was a Mr Peake whose official title, not perhaps to modem ears conveying his importance, was Cashier. He was an old man on the point of retirement and it caused no little stir when my father, by far the youngest clerk in the office, was appointed to take over from him. The possibility of this happening had been broached with my father, but the first intimation he had

Schooldays

J

that it was settled was when Mr Peake sent for him one Saturday morning to hand over the cash and the books. Partly because of ill-health, I did not make much progress at school and when, at the age of 8, I was enrolled in the junior department of King Edward VI Grammar School, Stourbridge, I was put at the bottom of the lowest form. At the bottom I stayed for the whole of my first year although it is fair to say that my report at the end carried the Headmaster’s comment in red ink, “handicapped by absence”. The result was that I was one of half-a-dozen or so boys who were not promoted to the next form. Every week the marks given in the various subjects were totalled and an order of merit produced. This was solemnly read to each form by the Headmaster in person. I had become so used to being at the bottom that it was quite a shock when, at the end of the first week of the new school year, I found myself third. The shock was also a stimulus and I did not, from that point, look back. The first form was the only one in the school to have a form mistress in charge of it instead of a form master. Her name was Miss I. D. Druller and she also taught English in the Upper School. One of her activities was to make the costumes for the annual Shakespeare play and later on I got to know her quite well in this connection. One year we did Julius Caesar and all wore togas. In 1967 I learnt from a young cousin attending the same school that Miss Druller was still teaching there. I wrote to her and had a reply in handwriting still familiar, although I had not seen it for nearly 40 years. With an unerring sense of what was fitting she addressed me by my surname, as she would have done when I was at school, beginning her letter “Dear Wilkes”. My grandfather on my father’s side also suffered with his breathing. This was partly as a result of a lifetime spent underground in the collieries of South Staffordshire. He described himself, on my father’s birth certificate, as a mining engineer but later on, when the regulations relating to mining were tightened up and managers were required to have certificates, he was, to his great disappointment, given only an under-manager’s certificate. Nevertheless, he took the prescribed ex­ aminations and became fully qualified when he was nearly 50. He had lost two joints from one of his fingers in a mining accident and I remember, when I first noticed this, being disturbed and frightened by it. I was 12 when he died; it was the first time that I had been brought face to face with the fact of death and I was much affected. If my grandfather had lived longer I think that we might have become good friends. He had no way with children, but we shared a genuine

4

Memoirs of a Computer Pioneer

interest in scientific things and I can see now that he was making attempts to communicate. My mother’s grandfather was bom in County Mayo in the west of Ireland in 1809 and came to England during the potato famine. He did not, as many of his compatriots did, go on to the United States, but settled in England. My mother’s father died when she was a small girl and her mother died when she was 12. My mother was one of a pioneering band of women who went into offices in their hobble skirts and worked the new-fangled type-writing machines. She used to talk to me about her office days and she had obviously enjoyed them very much. It was her misfortune on marriage to be taken away to a strange town, and she made few friends in later life. My school, as befitting an ancient foundation, had a strong corporate sense which did not have to be bolstered up by the wearing of a school uniform—except for a school cap, the wearing of which on the way to and from school was strictly insisted on—or by compulsory games. In these respects it resembled the majority of boys’ day schools of the time. School games took place after afternoon school and on half­ holidays. I was a shy boy and nobody did anything to encourage me to take part. Looking back, I can see that this was a pity. After four years altogether in the junior school, I passed into the main school. Here, the stream of about 25 boys that I was in was joined by another stream of new entrants. These consisted almost entirely of boys who had won scholarships from state-run elementary schools and a few of them overflowed into my form. This was the origin of the 11 -plus entry of the post-war period and contained a similar element of chance. The scholarship boys ranged from the very able to the very dim. However, of the boys that I remember who eventually obtained university scholarships, a clear majority had entered in this way. For me, the great excitement of going into the main school was that I would begin the study of science and mathematics. I cannot remember an age at which I did not know that I would become a scientist or an engineer. My favourite toys were mechanical ones and I amused myself with electric batteries, lamps, and bells, mostly pur­ suing the experimental method, but receiving some help from a sym­ pathetic uncle. I had a few books which must have come from my grandfather, though in what circumstances I do not know, and these I read and re-read. Some of them were fairly modem handbooks dealing with the installation of electric lighting, electric bells, and so on, and some were old-fashioned books on static electricity in which a typical illustration would be of a hand emerging from an immaculate

Schooldays

5

shirt-cuff and holding a suspended pith-ball near to the anode of a frictional electric machine. It was a pity that I had not access to an up-to-date library with someone to guide me through it. In the main school we began a four-year course leading to the Cambridge School Certificate examination. The papers and standard required closely resembled those for the Ordinary Level examination which replaced it in later years. In order to obtain a certificate, however, one had to pass in English, mathematics, a language, and two other subjects, all at the same examination. Most of the boys did this without difficulty. For the final year a small measure of specialization was permitted and I dropped geography and history. The more mathe­ matically inclined took two papers of additional mathematics as well as the regular papers. These gave me my first introduction to differential calculus and analytical geometry. We had a particularly keen and able mathematics master who, by the sacrifice of some of his spare time, made it possible for a small group to take a third paper of additional mathematics, namely, a paper on mechanics. I rewarded him by ob­ taining a distinction. Broadcasting started in 1922, but we did not have a “wireless set” until about two years later, when my father bought a rather ambitious 4-valve affair with an Amplion Dragonfly loudspeaker. I immediately began to make crystal sets and to save up money for my first valve. This was an Osram bright emitter that cost me twelve shillings and sixpence. The local station was 5IT at Birmingham, about 8 miles away, and this could be heard clearly enough on a crystal set provided that no-one rustled a newspaper in the room. One could also receive the long-wave station 5XX at Chelmsford, later moved to Daventry. The change from British Broadcasting Company Ltd, a consortium of companies in the electrical industry, to the British Broadcasting Cor­ poration, a nationalized concern, made little difference. At about this time I began to take regularly the Wireless World. This excellent journal published constructional articles containing complete designs for receivers that were quite advanced for the period and tutorial articles on the more theoretical aspects of the subject. It was through reading the Wireless World that I laid the foundation of my knowledge of electronics. Prominent among the contributors from 1925 onwards was W. T. Cocking. He eventually became editor and one day, much later in life, at some function where we were all wearing name badges, I found myself standing by him and was able to thank him for what I had learnt from his journal. He retired from the editorship only a few years ago.

6

Memoirs o f a Computer Pioneer

When I was about fourteen and a half the Wireless World published a sketch of a design for a folded exponential loudspeaker hom with a 2 ft square mouth. This was supposed to be built of blocks of wood planed to shape in such a way that when they were assembled an internal expanding channel of correct dimensions would be formed. An ingenious reader wrote to the editor some weeks later to suggest that boxes with wooden ends and cardboard sides filled with sand could be used instead of the wooden blocks. I fell for this and sought my father’s help in getting the necessary materials. I had not bargained for the weight of the sand. I can still see Joe Brown struggling through the back gate of our garden with the bag containing it. The loudspeaker, when finally finished, was too heavy to move and remained firmly rooted to the kitchen floor where it had been built. It worked as expected and the quality of reproduction (we did not then say hi-fi) was much admired. Its unfortunate tendency to leak sand on to the floor from time to time was nobly borne by my mother. In 1929 a newspaper article appeared in which sweeping claims were made for a new type of radio receiver known as the Stenode Radiostat. This was a supersonic heterodyne with a very sharply tuned intermediate frequency amplifier and frequency correction in the audio amplifier to boost the higher frequencies. This led to doubts being cast on accepted ideas about side bands and the band width necessary to transmit signals. There grew up a school which, as Professor G. W. O. Howe put it, regarded side bands as “a product of the imagination intended for the restraint of radio communication”. Quite a controversy raged in the correspondence columns of the various journals. No less a person than Sir Ambrose Fleming, then 81 years old, published an article in Nature in which he supported the rebels. Sir Oliver Lodge, who was one who knew his physics, put Fleming right in a kindly letter in which he observed that to talk about a sine wave of varying amplitude was an inexactitude, adding, however, that he was rather sympathetic to heresy even if he could not support this one. There were, however, some genuine points of uncertainty to clear up and the Radio Research Board appointed an investigating committee that reported towards the end of 1932. F. M. Colebrook, who had already contributed some sensible letters and papers on the subject was the author of the report. It effectively dashed any hopes that the spacing of broadcasting stations in the frequency spectrum could be reduced, or that wide-band television signals could be transmitted on medium wave lengths. Looking back on this controversy and on similar ones, one cannot help feeling how much the present generation of engineers

Schooldays

7

have gained over their predecessors by being thoroughly grounded in physics. The choices in the scientific Sixth Form at King Edward VI School were between physics and chemistry with some mathematics on the one hand and physics with a much more advanced study of mathe­ matics on the other. I chose the latter without much hesitation. I think that it was already clear to me that my life would be in physics or in physics-based engineering. I had seen enough to realize that there was a magic power in mathematics and I burned to be initiated hilly into that mystery. Although I did not do chemistry in the Sixth Form, I got to know the senior chemistry master, Mr J. Timbrell, very well and learned a great deal from him in an entirely different sphere. Mr Timbrell’s passion was radio and he introduced me to amateur transmitting. He held a transmitting licence with two call signs; one, G60I, was for a fixed station at the school and the other, G60J, was for a portable station. Before one could be authorized as an operator one had to pass an official Morse test. Since in those days Morse was still being used for the inland telegram service, it was possible to take the test at the local Post Office. After some intensive practice, I attended one day early in 1931 and duly passed. I could now be authorized to operate a station. Amateur transmitting enthusiasts, or “hams” as they were called, were always engaged in rebuilding their stations, or their “rigs” — again to use the jargon. Mr Timbrell was himself engaged in a great and ambitious re-build of G60I and he asked me if I would like to build some portable equipment for G60J. This was to operate on the band of frequencies about 1.6Mc/s that was useful for short distance communication in telephony. We always called this the top band. I did the receiver first. It was really a re-build of a broadcast chassis with one screened grid radio frequency amplifier, a rectifier, and an audio amplifier. Power supply was from an accumulator and rotary converter. When I had got this working, I was allowed to go on to the transmitter. This did not take so long, since a low-powered trans­ mitter is a much simpler thing than a receiver. When the rig was complete Mr Timbrell allowed me to operate it from my home. I have heard it said that there is no better way of learning about the sea and the science of navigation than by messing about in boats. The same is true mutatis mutandis of messing about with transmitters. My association with Mr Timbrell gave me my first experience of the way in which a strong common interest in a technical subject can break

8

Memoirs o f a Computer Pioneer

down barriers of age and status. Most boys I suspect found Mr TimbreU more than a little unapproachable. Those who shared his enthusiasm for amateur radio—and I was not the only one—he would meet on equal terms and treat as though they were grown up.

2 Undergraduate years

When, in the summer of 1931, my father took the decision to send me to Cambridge neither he nor I had had any contact with a Cam­ bridge college, and it was, therefore, a matter of starting from scratch. People chose their colleges for a variety of reasons. In my case, the choice was not a difficult one. My Headmaster, J. B. Boyt, had been at St John’s College and had taken the Mathematical Tripos in 1898. Moreover, A. J. Bennett, one of my form mates, was going to St John’s that year having won the Senior Mathematical Scholarship. Bennett was of my own age, although he had been in the Sixth Form longer. In deciding to send me to Cambridge, my father was acting against the advice of my Headmaster who thought I was not ready. He wanted me to stay at school another year and try for a scholarship myself. I was, however, already 18 years old, the year that I had lost in the first form having followed me through the school. Sometime in August 1931, my father took me to Cambridge to be interviewed by my future tutor, Mr J. M. Wordie. We stayed at the Lion Hotel in Petty Cury and, at the time appointed, made our way to St John’s College, where we were directed to E Staircase, New Court. It was, I remember, a showery morning and rather cold for the time of the year. We chanced to meet Mr Wordie at the bottom of the staircase and he whisked me up to his rooms, leaving my father, somewhat surprised, kicking his heels in the court. I got on well with Mr Wordie, although his strong Glaswegian accent gave me some trouble. He must have been satisfied with me because, before he sent me away, he told me that I could come up in October. I found my father sheltering by the bridge and gave him the good news. We set off for home, my father driving. The car was a Singer 10, then somewhat elderly. It had a vertical windscreen and the throttle pedal was in the middle, between the clutch and the brake. My father

10

Memoirs o f a Computer Pioneer

was pleased and happy. As for me, I was excited at the prospect of going to Cambridge and “old immortal words sang in my breast like birds”. This euphoria continued for fifty miles, at which point the engine began to make odd noises. We consulted an AA patrol on point duty at the crossroads just before Weedon Hill. In no time he diagnosed the trouble; we had run a big end bearing. There was nothing for it but to leave the car in his charge and make for Weedon railway station. The gods must have rocked with laughter. Of the various possibilities open to me when I went up to Cambridge, the most obvious were to take the Mathematical Tripos or to take the Natural Sciences Tripos*. The latter would have involved starting with two years of physics, chemistry, and some not very exciting mathe­ matics. The course for the Mathematical Tripos, on the other hand, included a good deal of physics, but no laboratory work. Since math­ ematics was what I was hungry for, I decided, without serious con­ sideration of the alternatives, to take the Mathematical Tripos. Although I never regretted this, I did feel rather deprived during my under­ graduate years in that I never went into a laboratory. In Cambridge one does not look to one’s tutor for instruction in the subjects one is studying. His role is to provide an administrative link with the College and to act as a fatherly figure to whom one can go for advice. Mr Wordie was a geographer with strong interests in the polar regions. In his youth he had been to the Antarctic with Shackleton; he was one of the party who were marooned on Elephant Island and only rescued in the nick of time. When I met him he was settling down and was said, in consequence, to be more likely to go to the Arctic than to the Antarctic. One year he led an expedition to Greenland and, on his return, showed us a movie—it was in colour, which was then rather a novelty —of some Eskimos dancing. One of the dances was ended by the local missionary rushing in among the dancers and breaking it up. Wordie remarked drily that they were not supposed to do that dance. Much later, Wordie became Master of the College and was knighted. He was Chairman of the British Committee for the International Geophysical Year 1957—8. In his latter years he suffered a decline, but when I first got to know him he was alert and shrewd, though lacking in the social graces. His leaving my father in the rain, when he interviewed me, was quite typical. It was customary to pay one’s respects to one’s tutor at the beginning and at the end of each term. I saw Wordie on my second day in iSTripos is the name given in Cambridge to an examination taken by candidates for an honours degree.

Undergraduate years

11

Cambridge and then waited on Mr Ebenezer Cunningham, Director of Studies in mathematics. It was at this point that I began to realize that there was something in what my headmaster had said and that my father had set me a challenge by sending me to Cambridge after only two years in the sixth form. Scholars—that is, holders of College scholarships—normally went on to second year lectures at once, relying on their ability to take Part I of the Tripos at the end of their first year without specific preparation. When it came to Part II they took, in addition to the regular papers included in what was known as Schedule A and taken by all candidates, six additional papers on specialized topics in Schedule B. Those who were less well prepared took a slower course and did not attempt the papers in Schedule B at all. In my case, Mr. Cunningham suggested a compromise, namely, that I should go to some of the first year lectures and some of the second year lectures. However, I found the first year lectures tedious and I soon realized, by talking to my friends, what I was missing. I, therefore, began to go to the full range of second year lectures. The decision was made easier for me by the fact that the principal course which Mr Cunningham had suggested I should omit was given by one of the few really good lecturers in the Faculty, Mr A. E. Ingham, who lectured on real variable. The fact that everyone took the same examination whatever the lectures he had attended was a distinct advantage for anyone in my position, since no firm decision had to be taken at an early stage as to whether he should take the fast or the slow course. It was, however, felt to be a defect of the system that a person taking the fast course was not in step with his examinations and the year after I took the Tripos a major reform was introduced. Schedule A and Schedule B became two separate examinations known as Part II and Part III respectively. Those who were well prepared when they came up would omit Part I, and would take Part II at the end of their second year and Part III at the end of their third year. Others would take Part I at the end of their first or second year and Part II at the end of their third year, omitting Part III altogether or devoting a fourth year to it. This was, no doubt, a valuable reform, but it would not have suited me at all and, if it had come a year earlier, I doubt if I would have made the grade. I had been in Cambridge some few weeks when I received a message to the effect that my father was coming to see me. I assumed that this was to be a normal paternal visit, but he was, in fact, coming to tell me that my mother was to have a serious and dangerous operation. It was obvious that I would have to go home with him. We travelled

12

Memoirs o j a Computer Pioneer

by train across country to Birmingham where we were met by Joe Brown. I was plunged from an active and exciting new life that I was enjoying to the full into a situation that was grave in the extreme. The operation necessitated the removal of a breast, and it seemed at one time as though my mother would not survive it. Fortunately she did, and lived for many years afterwards. As soon as it appeared that she was no longer in immediate danger, I felt that I could leave my father and return to Cambridge. Altogether, I had missed ten days of term. Cambridge regulations required that, in order to count a term towards the nine required for a degree, a student must spend three quarters of it in Cambridge. Normally he resides during the eight weeks known as Full Term. As I had missed ten days, it was necessary for me to make the time up by staying on after everyone else had gone. I quite enjoyed those extra ten days, even though the social life that I had been finding so agreeable came to an abrupt end. I was able to use the time to fill in the gaps in the term’s work and I was also able to take stock of my situation in regard to the examination that I would have to face at the end of the year. I had, in fact, learned much more mathematics during my last two years at school than some boys might have done. This was entirely due to my sixth form master, Mr H. E. Carpenter, who had taken a first class honours degree at Oxford and had joined the staff at the same time as I entered the sixth form. Instead of teaching us in a class, he set us individual work to do from books, giving us help with difficulties as we required it. I worked with another boy, S.C. Compton, and, together, we progressed at a fast rate. Compton went up to Cambridge the year after I did and I saw a good deal of him there. I lost touch with Carpenter, who left the school shortly afterwards and accepted a statistical post with the West Sussex County Council. He was not good at controlling a class of unruly boys and I think it probable that he was not very happy as a schoolmaster. However, he gave me the stimulus and opportunity that I needed and I am conscious of the debt that I owe him. Lectures were provided by the University, not by the colleges. Since, however, the University was short of lecture rooms, it was the practice for the mathematical lecturers to lecture in their own colleges. The lectures were fitted into consecutive one-hour time slots without any regard to the distances between colleges; the result was that we often found ourselves rushing from one side of Cambridge to another in the few minutes allowed between the end of one lecture and the beginning of the next. No doubt the exercise was thought to be good for us.

Undergraduate yean

13

Mr Cunningham lectured in St John’s on mechanics and gave a crisp and carefully shaped course of lectures that was a model of its kind. He was using the inhx notation for scalar and vector products that year for the first time as a result, he said, of some consultation that had taken place between lecturers in various universities. Cun­ ningham had been Senior Wrangler in 1902 and had come under the influence of Sir Joseph Larmor, Lucasian Professor of Mathematics in the University and a Fellow of St John’s. Larmor, along with Lorenz in Germany, had played a large part in the development of the classical electron theory and in the early development of ideas that led to the special theory of relativity. Cunningham took up these subjects and, as he once said to me, was right in the forefront of the field. He had left Cambridge to work elsewhere after taking his degree, but he was tempted back by the offer of a post in the College. In consequence, he became heavily involved with teaching and administration. At both of these things he was very good and the College and his pupils owe much to him. It was, however, clear from what he said that he regretted not having got back into research. When Cunningham retired from his Lectureship, a new career awaited him. He had long been interested in religious affairs and he put his abilities at the disposal of the Con­ gregational Union of England and Wales. He became Chairman in 1953 and in that capacity attended the coronation of Queen Elizabeth. In his later years, Cunningham retained his powers to an extra­ ordinary degree. It is the custom in St John’s that, when a new Master is to be elected, the Senior Fellow should take the initiative in promoting the informal discussions between the Fellows that precede the formal election in the College Chapel. It fell to Cunningham to do this on three separate occasions. Each time he performed his duties to per­ fection. On the last occasion he was 88 years old, but he took the chair with confidence at slightly tense meetings, seemed to know who was who and what was what, and showed no signs of deafness except when he thought it politic. He died in 1977 at the age of 95. S. Goldstein, who lectured to us on electro-magnetic theory, was also a Johnian. He and Cunningham, together with M. H. A. Newman and F. P. White, formed the team of College supervisors in mathematics. Each term a student was allocated a supervisor to whom he would go twice a week, usually in company with two or three other students, for an hour’s informal teaching. In my first term, because of the ambiguous status to which I have already referred, I was put with two other men in a miscellaneous group. Newman was our supervisor and when we went to him for the first time he obviously did not know what to do with us. The lecture courses had hardly started and our

14

Memoirs o f a Computer Pioneer

backgrounds were very different. He decided to give us an impromptu lecture on matrices. As far as I was concerned, he could not have done better. The material was entirely new to me and I felt that it was exactly what I had come to Cambridge to get. F. P .White had great geniality and warmth of character. His speciality was projective geometry, a subject for which he had great enthusiasm, but, unfortunately, no gift for teaching. The subject owed its place to the influence of Professor H. F. Baker, who had been, and still was, a powerful figure in Cambridge mathematics. There was a whole paper on it in the Tripos and no candidate for high honours could afford to neglect it. It was curiously unconnected with the rest of contemporary mathematics and was, I think, already becoming oldfashioned. If it had been well taught, I might have found it interesting, particularly as it was the only subject then taught in Cambridge from an axiomatic point of view. As it was, I fretted at having to spend so much time on a subject so devoid of application in physics and en­ gineering. Even now a feeling of resentment arises within me when I think of projective geometry. Although I was reading mathematics, I was determined to follow up my interest in radio. In search of information I began to penetrate into the University Library, then still housed in the Old Schools and open to undergraduates during the afternoons. Although radio had developed from being a subject for inventors and experimenters into a serious branch of engineering, very few textbooks had appeared in which an adequate scientific treatment was given. There was E. B. Moulin’s book on high frequency measurements, a second edition of which had just appeared. This contained much more general material than its title might suggest. There was also a book by Mcllwain and Brainerd entitled “High frequency alternating currents”, which I had seen reviewed and was delighted to find in the library. These authors worked at the Moore School of Electrical Engineering in Philadelphia, an institution of which I shall have a good deal to say later. I delved into this book avidly, although much that it contained was above my head. A book of a somewhat different character that I also found useful was by L. B. Turner of the Cambridge University Engineering Department. This was entitled “Wireless” and included, among other things, a lot of information about the Post Office long wave station at Rugby (call-sign GBR) which was, although I did not know it then, to provide facilities for my early research. In my second year I attended Mr Turner’s lectures in the Engineering Department. From my point of view, it was a very good course and I remember particularly some remarks on spark transmitters, which

Undergraduate years

15

he made by way of parenthesis, I suppose to avoid giving us the impression that he thought that spark transmitters had a future. I did not know that so much theory went into the design of a spark trans­ mitter and I was fascinated. Mr Turner’s course was the only one on light current electrical engineering then offered in Cambridge. One course may not seem very much, but at that time few engineering departments paid any attention at all to the subject and most of the radio and electronic engineers of my generadon were trained in physics departments. I could hardly expect to go on working with G60J after I had left King Edward’s School and I lost no time in applying for an amateur radio licence of my own. This came through some time during the course of my first year, and the construction and operation of an amateur station became my principal spare time activity in the va­ cations. I lashed up a top band transmitter for talking to the friends that I had made while operating G60J, but concentrated my main effort on equipment for 7 and 14 Mc/s. On these frequencies one did not expect to make contact with anyone at all near, since the wave that travels along the ground is very rapidly attenuated. One expected instead to make distant contacts, via the ionosphere. For this purpose, Morse was more suitable than telephony and caused less interference to other stations; indeed, the bands were so crowded that many people, including myself, considered it bad form to use telephony at all. Even with the very low power of 10 watts, which was all that was permitted by the British licensing authorities, it was possible to work stations all over the world. I shall never forget the thrill of my first contact with an amateur in the United States. The time was, however, rather a discouraging one for the amateur interested in DX, as long distance working was called, since the sunspot cycle was on the wane and transmission conditions were becoming steadily more difficult. A new interest, however, was growing up in much higher frequencies and I started working on 56Mc/s with T. L. Herdman, an old school friend who was also addicted to amateur radio. On frequencies as high as this, transmission beyond the line of sight depended on dif­ fraction, and one did not expect to be able to communicate over long distances. At first our interest centred mainly in the design and con­ struction of equipment, but later we took a portable receiver on to a local range of hills and studied the diffraction patterns that were set up. The experience that I obtained with apparatus working at what were then considered rather high frequencies was useful to me later when I began to work on radar.

16

Memoirs o f a Computer Pioneer

I rather deliberately avoided getting deeply involved with amateur radio in Cambridge, since I felt that there were so many other things to do. I did, however, in due course, become a member of the Cam­ bridge University Wireless Society which had a fairly flourishing trans­ mitting section. I would sometimes operate the transmitter which was situated in Scroope House, a large mansion, since demolished, that then formed the headquarters of the University Engineering Depart­ ment. The transmitter was located in a cellar next to the coal-fired central heating furnaces, altogether a most unsalubrious situation. It was in the basement of Scroope House that I first met W. S. Elliott, who was two years junior to me and was reading natural sciences. Elliott became a close friend and, over the years, we have done many things together. Later on, the head of the Engineering Department took pity on us and fitted up some much better accommodation for us in the old stables. In the event, I got my first class in Part I without difficulty and began to feel a little more confident. During my first year I had met so many new ideas that I had suffered from severe mental indigestion; now I was finding that, although the contexts and applications might be different, the same ideas were beginning to repeat themselves. Even so, I did not find the work easy. The trouble with mathematics is that, however diligent you are in going to lectures and in learning the theory, you may still not be able to do the problems. Although most of a student’s time in his second year was taken up with Schedule A lectures, he could take a few Schedule B lectures, these being, as it were, the icing on the top of the cake. I went to Mr L. A. Pars on general dynamics, this being one of the most widely attended courses. A course by Cunningham on classical electron theory was, however, more in my line. The material it contained was outmoded from the point of view of an atomic physicist, but was of the first importance for a radio man. Eddington’s lectures on relativity were also well attended. The subject was still somewhat new and attracting a good deal of attention. Eddington had written a serious but non-mathematical book entided “Space, Time and Gravitation”. I had chosen this book as a school prize and I was glad to have the opportunity of learning something about the mathematical development of the subject. Eddington used to ride a bicycle to the lecture room and would lecture with a pair of cycling clips on his trousers. He lectured from an annotated copy of his book “The Mathematical Theory of Relativity”. Many people contrasted the polished performance that Eddington would give when delivering a formal lecture as a set piece with his hesitant and uncertain

Undergraduate yean

17

delivery when giving a class lecture. I followed him up to a point; beyond that I could follow the mathematics, but lost track of the physics. I do not think that this was altogether my fault. During my second Long Vacation I had plenty of work to do in revising the lectures, many of which—and this is an understatement— I had not clearly understood at the time that they were delivered. Part of the vacation, however, I spent happily writing an essay for the Adams Memorial Prize. This is a prize offered to undergraduates in their second year reading mathematics at St John’s. Among the subjects set in 1933 was “The Electron Theory of Metals”, which suited me very well. Candidates were referred to Campbell’s book on “Modem Electron Theory” and this, together with Cunningham’s lecture notes, provided the necessary material. I shared the prize with F. J. Stratford and I still have the two large volumes containing Adams’ collected works which, along with a few guineas, constituted the prize. In my third year I went to a course on the dynamical theory of gases given by F. C. Powell. It was then that I heard, for the first time, the name of Professor Sydney Chapman. During the course, we repeatedly fought our way through long and tedious multi-dimensional integrals; always at the end we had our satisfaction chilled by being told that Chapman had made a more elaborate calculation and obtained a superior result. I wondered who this remarkable mathematical genius was and what he was like. Later, when I came to know him well, I found that he carried his learning lightly. There was also a course on electric waves given by F. H. Woodward, a young Fellow of Selwyn. This was mosdy about radiation from a Hertzian dipole and refraction round a sphere. Woodward only had a few students, but I, for one, found the course very valuable. A few years before this time, E. V. Appleton had demonstrated experimentally the existence in the upper atmosphere of the reflecting region then known as the Heaviside layer. Various people had realized that the air in the reflecting region must be ionized and that the methods of the classical electron theory would enable the reflection of radio waves from it to be discussed theoretically. This had stimulated Cunningham’s interest and he announced for the Easter Term 1934 a course entitled “Wireless waves”. I attended this course and did a little reading around it under Cunningham’s guidance. To stay on at Cambridge and do research had long been my ambition and, now that I felt that I had a good chance of doing sufficiently well in the Tripos to obtain a research grant, I could make plans. The research grant was rather necessary, since I could hardly expect to go on living on my father after I was twenty-one. I was in no doubt

IS

Memoirs o f a Computer Pioneer

about what I wanted to do. Everything pointed to my going to work under Mr J. A. Ratcliffe in the Cavendish Laboratory, if he would have me. 1 knew several of his students and had seen some of the experimental work they were doing. Accordingly, I went one day to call on Mr Ratcliffe in his rooms in Sidney Sussex College. He received me kindly and seemed pleased at the prospect of having me as a student. He said that I ought to see Professor R. H. Fowler about making an application to the Department of Scientific and Industrial Research for a research grant. I duly saw Professor Fowler and no doubt I filled in forms, but I cannot remember. The important thing now was to concentrate on my work for the Tripos. The Schedule B examination differed markedly from that for Sched­ ule A, in that the quesdons required the reproduction of some piece of theory, rather than the solution of a problem. A student could choose freely from a very wide range of options and the merit of Schedule B was that it gave him the opportunity and the incentive to charge up his batteries, as it were, before beginning original work of his own. The examination was a long-drawn-out ordeal. There were six papers, each of three hours’ duration, taken on the Monday, Tuesday, and Wednesday of one week; there was then a gap and a further six papers, also each of three hours’ duration, on the Monday, Tuesday, and Wednesday of the following week. It is reported that, in the 18th century, the more difficult papers, which were reserved for candidates who had acquitted themselves with distinction in the main part of the examination, were taken in the examiners’ rooms in the evening and that wine and fruit were provided. There was nothing like that for us but, on the other hand, we took the examination in a sunny June instead of in the depths of winter in an unheated Senate House. The results were published on 12 June. Normally, following ancient tradition, one of the Moderators would read them out in the Senate House before they were put on the notice board. This was one of the few ceremonial occasions on which it was permissible to enter the Senate House without wearing academic dress and men from neigh­ bouring colleges would sometimes go in their dressing gowns. However, in my year, the custom of reading was dispensed with and the results were simply posted. There was a crowd around the notice board, but one look was sufficient. I had done what I hoped for. I sent a telegram to my mother and father and later in the morning I called on Mr Ratcliffe, who I found had already seen the class list. He assured me that I could now expect to receive a DSIR research

Undergraduate years

19

grant. He then told me to go away, have a good holiday and be back in a month’s time. Those were days when life was real and earnest. Now, students usually take the whole summer off and do not start research until the beginning of October.

1

With my mother when I was 4 1/2 years old

2 Aged twelve years

3

The car that broke down after my interview in Cambridge. I am sitting on the battery and my father is sitting on the running board. My mother is inside with her sister on her right.

4

Amateur radio station G5VF. Copying Morse (about 1933)

5 With my mother and father outside the Senate House on degree day (June 1934)

6

Taking tea in the Orchard Tea Gardens at Granchester with Vic Hughes (left) and Lyman Spitzer (1936)

7

My mother and father at the time of their silver wedding (1937)

8

The model differential analyser in Cambridge. J. Comer is following a curve on the input table, A. F. Devonshire is standing on the left, and I am on the right

9

Douglas Hartree with Phyllis Locket (later Mrs Nicolson) leaning over the output plotting table of the differential analyser at Manchester University

3 Post-graduate research

When I joined the Cavendish radio group in July 1934, it consisted of J. E. Best and F. T. Farmer, who were doing experimental work, and H. G. Booker who was a theoretician. There was also S. W. H. W. Falloon, who was helping with the experimental programme, al­ though not registered as a research student. An interested supporter of our activities, although not an active participant, was Dr W. B. Lewis, then newly appointed to a junior faculty position in the Cav­ endish. Lewis was a regular attender at the weekly colloquium held in Mr Ratcliffe’s college rooms after dinner. Earlier students of Mr Ratcliffe’s who had recently taken their degrees and gone away were E. L. C. White, F. W. G. White, and J. A. Pawsey. Shortly before I joined the group, Mr Ratcliffe had decided to re­ start work on the propagation of very long radio waves, a subject that had fallen out of fashion in the general switch of interest to short waves. Since very long waves are reflected in the lower regions of the ionosphere, he thought that their study would complement that of the absorption of short waves, which also takes place in the lower ionosphere. Best was already working on this programme and Mr Ratcliffe suggested that I should join it. Two series of experiments were planned. One was to be conducted with fixed measuring equip­ ment in Cambridge and the other with portable equipment, mounted in a caravan that could be towed behind a car. Best had put in a good deal of work getting the apparatus ready for these two experiments. It was now suggested that he should concentrate on the fixed apparatus and that I should take over the portable apparatus. Accordingly, I put the final touches to the equipment and did some mechanical main­ tenance on the caravan. The first results were obtained during the night of 9/10 August, when we towed the caravan some 40 kilometres to the east of Cambridge. This was my first introduction to night time

Post-graduate research

21

observing, of which I was to do a good deal during the next three years. I consider that I was extremely fortunate in joining a group with an active programme of observation and in being allowed to take part in that programme right from the beginning. Many research students had to serve an apprenticeship in which they learnt the experimental technique or the underlying theory of their held of research. In the Cavendish Laboratory there was a regularly organised course during the Long Vacation for newly-joined research students. I avoided this because I had joined from the Faculty of Mathemadcs. I would certainly have learnt something of value if I had gone on that course, but I am sure that I gained more by starting at once on observational work. In Cambridge no course work is required of a research student— although he is encouraged to attend any lectures that interest him— and the only requirement for the Ph.D. is that he should submit a satisfactory thesis at the end of three years. Relieved of the strain of preparing for an examination, I felt as Christian did when the burden fell from his back. Moreover, my curiosity about mathematics had now been satisfied and I felt that I had taken its measure as far as application to my sort of physics was concerned. I did not have, and indeed never have had, that interest in mathemadcal puzzles and fine points that characterize the natural theoretician. I looked forward to being able to apply the mathematics I had learnt to physical problems but, in the meantime, I wanted to establish myself as an experimentalist. I found that the experience with radio equipment that I had acquired as an amateur stood me in good stead and it soon became clear that I had lost nothing by not doing physics as an undergraduate. The Mathemadcal Tripos was, and to a considerable extent still is, mis­ named. It had given me a good grounding in mechanics and electro­ magnetic theory and also included material on spherical astronomy, geometrical optics and thermodynamics. Ratcliffe unerringly put his finger on my one deficiency, which was in physical optics, and this I was soon able to put right. It was not possible to make radio observations in the Cavendish Laboratory itself on account of the high level of electrical interference and the radio group accordingly did most of its work on the old rifle range on Grange Road. Two wooden huts sufficiently near to the road to have electric power constituted the headquarters of the group. These housed short-wave receiving equipment and what primitive workshop and laboratory facilities were available. One of the huts had built into it a small dark room used for developing photographic records. The other hut served partly as a garage for the caravan.

22

Memoirs o f a Computer Pioneer

There was a third hut, 50 yards away in open country, used to contain the fixed apparatus for long-wave measurements which needed to be well away from buildings. There was no electric power available in this hut and all equipment had, in consequence, to be battery operated. Heating was a problem and one had a choice between using a smelly oil heater and putting up with the cold. I usually did the latter. Present-day research students who are used to having plenty of equipment provided for their use would have found conditions rather primitive. We did, however, have just enough equipment for our needs and if one needed a potentiometer or other small component, one could go to a local shop and have the cost put down to the Laboratory. We were thus not completely dependent on the Cavendish storekeeper, Mr Lincoln. All the students and some of the staff were afraid of Mr Lincoln, who sported a rather fierce pair of waxed moustaches. In any case, Mr Lincoln did not stock modem radio components. The legend was that, if you asked him for a change-over switch and if he felt that you deserved one, he would issue you with a block of paraffin wax with some holes bored in it, some bent pieces of wire, and a small bottle of mercury. The experiments with the portable equipment in the caravan went very well. Best, however, was having much trouble with his equipment and decided to re-build it. By February 1935, he was just beginning to get it into operation again when most unfortunately he went down with jaundice. I, therefore, found myself charged with the final com­ missioning. Because of the good work done by Best, this went smoothly, and I got the first results in July. When, after being away some nine months, Best was well enough to start work again, he left me with the long-wave equipment and himself started a new series of exper­ iments with short waves. On the social level life was still very agreeable. Some Cambridge colleges rather abandoned their men when they had taken their B.A. degrees, but this was not the case at St John’s. We had our own table in the dining hall and, together with students who had come from elsewhere to do research in Cambridge, we formed a lively company. Mr Wordie allowed me to continue to occupy rooms in college during my first two years of research instead of going into lodgings in the town, and this was an amenity that I much appreciated. Of the research students at the B.A. table at that time I remember, particularly, Kenneth Craik, Jack Diamond, Stewart Marshall, and Sam Lilley. There was also Lyman Spitzer who came over from the States to spend the academic year 1935/36 in Cambridge. It was just after prohibition had ended in the United States and I remember him showing us a

Post-graduate research

23

New York speakeasy card. A few years ago, I looked Lyman up in Princeton, where he was then a professor and it seemed only yesterday that we were students together. Kenneth Craik had had a mainly arts upbringing and had taken a degree in philosophy, including some psychology, in Edinburgh. He came to Cambridge to do research under Professor F. C. Bartlett, head of the Department of Experimental Psychology. Craik was very adept at making things with his hands and would carry about with him a tobacco tin containing several small model steam engines that he had made, the smallest being truly minute. He could tell you exactly how many hours each one had taken him to make. He carried many other things in his pockets, including a thick bulging wallet containing papers and notes of all kinds. Often he could produce just the thing to illustrate the topic under discussion. Craik’s interest in gadgets, both electrical and mechanical, would not have been unusual in the Cavendish or in the Engineering Laboratory, but it was unusual at that time among people who worked in biological departments. Craik joined Bartlett’s group at a time when ability of this kind was just what was needed and possessing it put him in a key position. A new building came into use while Craik was still a research student, and Bartlett relied on him heavily for the equipping of the workshop and the ordering of materials for it. Bartlett was very much an establishment figure in the field of ex­ perimental psychology. His speciality was the study of the human senses, particularly vision; this carried with it an interest in the per­ formance of tasks in which those senses played a part. He had little time for the speculations of the psychoanalysts. He once expressed to me his feeling of indignation at Freud being everywhere regarded as a scientist, although he had never done any experiments. When the war came Bartlett’s advice was much sought by the Services. Craik stayed on in Cambridge and became Bartlett’s right hand man. It was he who actually performed the experiments on which Bardett’s advice was based. Craik’s reputation was already firmly established when, on 7 May 1945, he was knocked down and killed by a car in King’s Parade as he was on his way to attend the annual Commemoration Feast in St John’s College. Like many men of out­ standing promise who die young, he has become something of a legend; but in his case the reputation is not undeserved and he would undoubtedly have gone far. An enterprise of my first year as a B.A. was the founding of the St John’s College Graduate Croquet Club. At one time bowls had been played in the College after dinner on summer evenings, but this custom

24

Memoirs of a Computer Pioneer

had died out. Someone —it may have been F. J. Stratford—had the inspired idea that we should seek permission to play croquet on the paddock outside New Court. This permission was readily granted by the Junior Bursar, J. D. Cockcroft. In Cambridge it was, and still is, customary to wear gowns at formal dinner in Hall and we had no difficulty in deciding that we would wear them also for croquet. Whether this represented an assertion of traditionalist principles, or whether it was an example of the genial form that student protest took in those days, was never determined, but it is a fact that on at least one occasion some American visitors requested permission to take a photograph of us as we played, no doubt so that they could show it on their return home as an example of an ancient custom. The Graduate Croquet Club survived the War and there are now several other Croquet Clubs in the College. This is in line with a general revival of interest in the game, but it is nice to think that, as far as Cambridge is concerned, we began it. In February 1936 the calm of our little research group was shaken by the announcement that Appleton, who was then Wheatstone Pro­ fessor of Physics at King’s College, London, had been appointed Jack­ sonian Professor in the University, in succession to C. T. R. Wilson, and would take office at the beginning of the ensuing October. Appleton was the father of radio physics and we naturally wondered what the effect of his coming to Cambridge would be. Ratcliffe soon took an opportunity of remarking that he thought that things would go on very much the same as far as our group was concerned. This indeed proved to be the case. Appleton brought a number of people with him and, of course, attracted a larger group than Ratcliffe had had. A suitable laboratory was built for him near to the observatory where his students could do their experimental work, leaving us in undisputed possession of the accommodation at the old rifle range. This, inci­ dentally, had been greatly improved by the building of a small brick laboratory that provided much improved amenities compared with what were available before. Ratcliffe did, however, take the precaution of inviting Lord Ruth­ erford, head of the Cavendish Laboratory, to make a tour of inspection of the radio physics section, so, as he put it, that “he shall know what he has already”. I had often seen Rutherford about the Laboratory and had heard him lecture, but this was the first time that I came face to face with him. Although he had himself been interested in radio communication at the very beginning of his career and had indeed hoped to make some profitable invention in that field, we did not feel that our work in the radio group was very near his heart.

Post-graduate research

25

RatclifFe has, however, since assured me that Rutherford did in fact give the group his full support. Certainly, on the afternoon he visited us, he was on his best behaviour, showed interest in what he saw, and went away after giving us every encouragement. Early in March 1936, I attended a lecture given to the Cambridge Philosophical Society by Professor D. R. Hartree of Manchester Uni­ versity on the differential analyser. This was followed by a demon­ stration of a model machine constructed at the instance of Professor J. E. Lennard-Jones and housed in the Physical Chemistry Department. I had heard various reports from time to time about the differential analyser. I knew that it solved differential equations by mechanical means and plotted the results, but no details of its mode of operation had come my way, nor was I aware that a model differential analyser had actually been constructed in Cambridge. It was a model in the sense that it was built from Meccano parts, Meccano being a popular engineering toy that I, in common with practically every other boy in the country, had been brought up on. Professor Hartree had had the original idea of using Meccano for this purpose and with the assistance of Arthur Porter he had built a model at Manchester Uni­ versity and had been surprised to find that it was something more than a toy. The Cambridge model was built by J. B. Bratt, a man of great mechanical gifts, who had come to Cambridge when somewhat older than most undergraduates and had taken the Natural Sciences Tripos. Bratt did not use Meccano for those parts that were critical to the accuracy of operation and the machine was fully capable of doing useful work. As a piece of mechanism, I found the machine irresistible. More than that, I saw in it the answer to a need, for, in the course of my investigation of ionospheric models appropriate to the propagation of long-wave radio waves, I had encountered a differential equation whose solutions could not be expressed in terms of tabulated functions. I, therefore, lost no time in approaching Professor Lennard-Jones with a view to my being allowed to use it. He readily agreed and put me under the tutelage of Bratt, who was generous in the extreme. Before long the machine was producing the solutions that I wanted. Bratt was leaving Cambridge at the end of the year to take up a post at the National Physical Laboratory. Lennard-Jones must have seen that my heart was in this sort of thing, because he asked me if I would like to take charge of the machine when Bratt had gone. I jumped at the idea and Lennard-Jones arranged for me to be paid a small salary; this, too, was welcome since my DSIR grant had expired

26

Memoirs o f a Computer Pioneer

and I had no income other than from a small amount of hourly paid teaching. The understanding was that I would provide the technical assistance needed by anyone who had a problem suitable for putting on the model differential analyser and whose use of it had been approved by Professor Lennard-Jones; at the same time, I would be allowed to make use of the machine for my own private research. The first problem I did came into the latter class. Chapman had recently pro­ pounded a theory of the way in which solar radiation was absorbed by the ionosphere to produce the free electrons responsible for reflecting radio waves. I used this theory to calculate a series of diurnal ionisation curves for the atmosphere on the assumption that the electrons dis­ appeared by recombination. This was a problem ideally suited to the machine. It was well within its range and the accuracy obtained was very adequate for the purpose. The results were published some time later in the Proceedings of the Physical Society. In June 1937, Lennard-Jones asked me if I would help one of his research students, Miss Elizabeth Monroe, to try out the capability of the machine on a differential equation arising in the two-centre problem in wave machines. Here I provided only the technical assistance, since, as Elizabeth observed in her thesis, I had little personal interest in the problem itself; however, she did thank me for listening “with apparent patience” to occasional monologues on it and I certainly learnt much as her work proceeded. The problem strained the model differential analyser to the limit. As left by Bratt, the machine had only four integrators, but there was a space in the middle where, with a little re-arrangement, an additional one could be inserted. Elizabeth was very anxious that we should build the additional integrator, since she saw that it would make all the difference as far as her problem was concerned. Lennard-Jones agreed to provide the necessary funds and by the autumn we had drawn up the specification and ordered the necessary parts. I had spent many happy hours when young building things with Meccano, this being an English boy’s birthright. Elizabeth, who was American and a girl to boot, had been underprivileged in this respect. I therefore gallantly ceded to her the job of assembling the Meccano parts, only intervening to make sure that the nuts were tight. It is satisfactory to record that the new integrator was a great success. Shortly after taking charge of the model differential analyser, I indicated to Lennard-Jones that I would like to take the opportunity of my association with him to leam what I could about the quantum theory of atoms and molecules, and perhaps make some contribution

Post-graduate research

27

to the work of his research group. He accordingly suggested to me that I might like to do some calculations on a model of graphite with a view to finding how the potential energy varied with the assumed distance between the planes in which the carbon atoms were situated. I obtained some results which appeared interesting, but the work was interrupted by the war and I never came back to it. Theoretical chemistry, in the sense in which the term was used by Lennard-Jones and his associates, depended entirely on numerical calculation since there was no possibility of obtaining formal math­ ematical solutions. Most of the work was done on desk calculating machines. Perhaps because I had come to the subject from outside, I saw clearly how low the targets of achievement had to be in the face of mathematical and numerical difficulties. The subject certainly did not appeal to me as one on which I would wish to spend a major part of my working life. Even when the coming of digital computers had changed the situation radically as regards computing, the math­ ematical difficulties remained very great. I was later to find my early exposure to the subject of great value, since it enabled me to understand what people were trying to do in this held and where the real difficulues lay. The model differential analyser was not regarded as an end in itself, but as a step towards getting a full-scale one. I had no knowledge of what went on behind the scenes, but, judging by what was made public, the proposal for the establishment of a computing laboratory commended itself readily to Cambridge mathematicians and scientists. The first report on the subject was published by the General Board of the Faculties in December 1936. The opinion was expressed, perhaps somewhat prematurely, that computing machines had passed the ex­ perimental stage and must now be regarded as essential to the de­ velopment of applied mathematics. It was proposed that the University should acquire a differential analyser, similar to the one constructed by Metropolitan Vickers for Manchester University with the aid of drawings supplied by Vannevar Bush. Mention was also made of desk calculating machines, punched card machines, and a machine for solv­ ing sets of simultaneous linear algebraic equations invented by R. R. M. Mallock and pioneered by the Cambridge Instrument Company. I shall have more to say about the Mallock machine later. The total cost of capital equipment required for the Laboratory was estimated at about £10,000. It was suggested that the Director of the Laboratory should be one of the existing Professors, functioning part-time, and that there should be an academically qualified person in charge of the machines, assisted by a technician.

28

Memoirs of a Computer Pioneer

A strong floor would be needed for the differential analyser and various suggestions as to where the Laboratory might be located were canvassed. Lord Rutherford had expressed a willingness to find room for the differential analyser in the new Austin Wing of the Cavendish Laboratory, but he would not be able to find room for the other machines as well. No comments were made on this report when it came up for public discussion in the Senate House and it was approved by the University towards the end of February 1937. The principle of having a Computing Laboratory now having been established, the General Board published on 21 April a further report dealing with its organization. In this report the name “Computing Laboratory” was dropped and the term “Math­ ematical Laboratory” used instead. This was an error of judgement we had to correct thirty-three years later. The General Board proposed that Lennard-Jones should be appointed Director and that a University Demonstratorship (which in Cambridge is a junior Faculty appointment) should be established from 1 October 1937. Again, when the report was offered for public discussion, no remarks were made and the recommendations contained in it were formally approved in the middle of May. As soon as the developments that I have been outlining had gone sufficiently far, Lennard-Jones asked me whether I would like to be a candidate for the University Demonstratorship and gave me to understand that I would have his warm support. There was, of course, nothing that I would like better and on 9 June I was duly appointed, with tenure to commence at the beginning of the following October. Lennard-Jones showed great vision in proposing that the Mathe­ matical Laboratory should be set up as a separate Department of the University. He might easily have proposed the acquisition of a dif­ ferential analyser and other machines and made arrangements for them to be housed in some other Department. The fact that the Mathematical Laboratory existed as an independent Department in its own right, made it possible after the War for Cambridge to play its part in the development of modem computers and their applications without administrative problems having to be solved first. In other ways too it is now possible to see that Lennard-Jones was a man of more than usual vision. This was by no means apparent to all of those who worked under him before and during the War. He could be fussy at times and even self-important, and had a way of not always seeming to take his helpers fully into his confidence. On the other hand, he must have created a very favourable impression on his superiors as is witnessed by the fact that, during his war service, he became Chief

Post-graduate research

29

Superintendent of the Armament Research and Development Estab­ lishment and, subsequently, Chief Scientist of the Ministry of Supply. In 1953, after having been back in Cambridge for a short time only, he was appointed Principal of the University College of North Staf­ fordshire, but died the following year at the age of 60. I liked LennardJones as a man and our relations were always cordial. One of my jobs during 1937 was to attend on Mr Mallock in the Engineering Department and become acquainted with his machine which it was intended to buy for the Mathematical Laboratory. The Mallock machine was an analogue device and was capable of solving ten simultaneous linear equations in ten unknowns. It was based on the use of tapped transformers with the windings connected to form a network. The accuracy obtainable from such an arrangement might be expected to be very low because of losses in the transformers. What made the Mallock machine give a useful accuracy—one part in 1000 in favourable cases—was the use of a highly ingenious feed­ back circuit, known as a compensator, associated with each transformer. As a piece of electronics, this was well ahead of its time. Mallock had devoted the major part of his life to the machine and it had been taken up by the Cambridge Instrument Company, then presided over by C. G. Darwin. Unfortunately, the machine had not been a com­ mercial success and this had made Mallock rather a disappointed man. However, the prospect of the machine being installed in the Mathe­ matical Laboratory and being put to practical use gave him some pleasure. In order to solve a set of simultaneous equations, one had first to set the coefficients on an array of digital switches. The roots were then obtained by adjusting another switch until a galvanometer showed zero. This had to be done for each root in turn. When I got to know him, Mallock was experimenting with a device based on the use of telephone relays for performing this operation automatically and printing the result on a paper strip. Although this gear came with the Mallock machine, it was not fully developed and we made no attempt to use it. However, it gave me my first introduction to the use of telephone relays in computing, or rather control, circuits and to some of the tricks that one can play with them. It was obviously important that I should visit Manchester and see the full-scale differential analyser in operation. This trip was the oc­ casion of my first meeting with Professor Hartree who in later years became my close counsellor and friend. He would go to any amount of trouble to help people. On this occasion, not only did he invite me to stay at his home, but he met me at the station and drove me to

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Memoirs o f a Computer Pioneer

the University. Here he introduced me to Arthur Porter, who lent me a Laboratory coat, gave me an Allan key and let me try my hand at making some adjustments to the set-up of the differential analyser. Setting up a mechanical differential analyser was not a job for anyone who liked to keep his hands clean; it consisted of arranging in the desired configuration a lot of oily shafts and gears. During my visit, Hartree talked to me about some of the computing that he was doing with a desk machine. In spite of his modest manner, I sensed that here was a level of professionalism in computing far beyond anything that I had encountered up to that time. He also took me along to see the people at Metropolitan Vickers who had been responsible for the building of his machine and who were expecting to be responsible for the Cambridge one. The problem of where the Mathematical Laboratory was to be housed was resolved when it was found possible to make available space in the north wing of a building about to be vacated by the Department of Anatomy. This building dated from 1890 and needed some renovation and adaptation to its new purpose. The anatomists assured us that the strong smell of formaldehyde would soon disappear if we left the windows open and this indeed proved to be the case. By the beginning of 1938 Metropolitan Vickers, in common with other engineering firms, were heavily loaded with military contracts and progress on the differential analyser was slow. The work necessary in the old Anatomy School was the responsibility of the Building Syndicate of the University and had hardly started. I sensed that each party was waiting for the other. Lennard-Jones was attending the Indian Science Conference in Calcutta and had left me temporarily in charge. I therefore decided on what I thought to be a reasonable date and informed Metropolitan Vickers that the building would be ready by then; simultaneously, I informed the Secretary of the Buildings Syndicate that that was the date on which the machine would be ready for installation. Rather to my surprise, this simple manoeuvre worked and things began to move. Later in the year I paid a further visit to Manchester to approve a new design of torque amplifier and to discuss some of the details of installation. All was going well except for the international situation and the War broke out before the dif­ ferential analyser could be installed. The entire building was imme­ diately taken over by the Ministry of Supply and as soon as the new differential analyser was in working order it was used for ballistic calculations. By then, as I shall explain in the next chapter, I had left Cambridge to undertake war work of a different kind. Lennard-Jones remained in charge of the laboratory until he left to take on wider responsibilities.

4 W ar

When I went to Cambridge, the First World War was 13 years in the past and the hope that we might have a long period of peace in front of us was beginning to be seriously disturbed by events in Italy and Germany. I found myself in my first year beginning to think seriously about war as something that might actually come and to consider what my attitude to it ought to be. In the 1920’s there had grown up a great feeling of revulsion against the futility of war, a feeling that had its roots in the nature and the scope of the military operations conducted during the First World War on the Western Front. Books had appeared describing the experiences of young officers who had served in the trenches and I found a row of these on a shelf in the Union Library. Some of them—by Sassoon, Graves, Carrington, and others —are still read and perhaps now have a period flavour. Their message at that time was more immediate. Even so, the sense of purpose and national struggle which sustained their authors in the trenches had evaporated like rain on a summer day and what was left was cold horror. It is not only soldiers who assume that the next war will be like the last one, and I found myself facing the possibility that service in the trenches might come my way too. I frilly shared the contemporary feeling about the futility of war and, as an adolescent, had looked for idealistic solutions. In Cambridge I came to realize that questions of right and wrong cannot be settled by rule of thumb and, moreover, that to run counter to the current of the times would, in the absence of very clear grounds, be a recipe for unhappiness. I decided, therefore, to put the moral issues on one side for the time being, and, in the phrase of a later generation, to play it by ear if and when the time came. The year 1938 started well for me. I took my M.A. degree, which in Cambridge one takes as a matter of right a certain length of time

32

Memoirs o f a Computer Pioneer

after one’s B.A. In a sense, taking it is a pure formality, but it does give membership of the Senate and other privileges that are of value to a young don. Early in the year I bought my first car, a brand new Morris 8, which cost me £139.10s.Od. At the end ofJune I drove the car up to Scotland with Lyell Herdman as a companion to visit the British Empire Exhibition at Glasgow. This was the last Empire exhibition to be held. The scale was very much smaller than that of the Wembley Exhibition of 1924/5 that I had also attended and it was open for a much shorter time. I have been to quite a number of exhibitions at various times, and it is surprising how little they leave by way of a coherent impression. I have on the whole a clearer recollection of Wembley than of Glasgow. A few years ago, after giving a lecture at the Wembley Conference Centre, then newly opened, I walked over the former site of the Exhibition. The facades of some of the temporary buildings erected to house the exhibits were still there after 50 years and immediately recognizable. However, I must confess that what I mainly remember about Wembley is the amusement park; even now I have a thrill when I think about it. Later in 1938 I drove down to Chelmsford to attend a Summer School at the Marconi College of Wireless Telegraphy. It was very unusual in those days for a commercial company to organize such an event for the benefit of staff in Universities. We were most comfortably accommodated in the hostel associated with the College and a lot of work had obviously been put into organising the course. Marconi’s business was largely concerned with the provision of communication and broadcasting transmitters of all sizes, together with communicadon receivers. Going through the factory were a range of transmitters and receivers destined for the army of a Middle East country. All the transmitters had series modulation, a system that was new to me. Whether it had been adopted for economic or technical reasons, or because of something in the patent situation, I do not know; at all events, I stole the idea and used a series modulator very effectively in a top-band transmitter that I built shortly afterwards for amateur use. The Marconi Company was very strong on the fundamental side and there was much to be learned from their frequency standards and measurements department. Near Chelmsford, at Great Baddow, were the headquarters of a group under T. L. Eckersley concerned with research in wave propagation.This had been formed by Marconi immediately after the First World War, when it became important that the reasons for the ap­ parently erratic behaviour of radio direction finders should be thor­ oughly understood. Eckersley had been given much freedom in doing

War

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fundamental research and had maintained quite close contact with the academic community, although, for some reason or another, he and Appleton never got on well. Perhaps partly because of his in­ dependence of mind, Eckersley’s work did not receive the recognidon it deserved, but looking back it is possible to see that some of it, particularly his work on ionospheric scatter, was ahead of its time. F. T. Farmer and S. Falloon, former colleagues of mine in the Cavendish Radio Group, were both working with Eckersley at the time of the Marconi Summer School. I was back in Cambridge in time to attend the summer meeting of the British Association for the Advancement of Science which was being held there that year. This was my first experience of a large scientific congress and I enjoyed it enormously. The University and the colleges were generous in their hospitality, and the week went by in a round of interesting lectures and enjoyable receptions. Calculating machines figured on the programme and I gave a lecture on the Mallock machine and afterwards demonstrated it. The model differ­ ential analyser was also on view and there was an exhibition of desk calculating machines. The Munich crisis came with a terrible impact. I had gone home to Worcestershire after the British Association meeting and was in­ tending to return to Cambridge at the beginning of October, when Hitler suddenly made his demand to Czechoslovakia for the cession of the Sudetenland. He was fully prepared for war; Britain and France were not. On 15 September, Mr Chamberlain flew with his staff to Berchtesgaden; on 22 September, he went to Godesberg. Travel by air was far from being the normal way of getting about at that time and this added to the drama and intensity of the events. On 25, 26 and 27 September, the government took emergency measures. The fleet was mobilized, RAF personnel on leave were recalled, and, most ominous of all, civilian respirators were moved from the central stores in which they had been held to local depots ready for issue. I felt that if the balloon were going up my proper place was in Cambridge, where I would be more in touch with events and where, perhaps, my own role in the coming hostilities would become clear. Accordingly, I drove to Cambridge on Wednesday 28 September. When I arrived the distribution of respirators to the civilian population was in full swing at a small infants’ school very near to where I lived.* The atmosphere was everywhere tense. Next day Mr Chamberlain flew to Munich, with what result everyone now knows. :fWhen I next went into that school it was nearly twenty years later and my own son was attending it.

34

Memoirs o f a Computer Pioneer

A new piece of news burst at the same time, namely, that Mr Duff Cooper, who held the important Cabinet appointment of First Lord of the Admiralty, had resigned. No-one knew what to make of this. However, by the next day, the crisis was on its downgrade and, as one walked about the streets, one could see the relief on people’s faces. By 5 October, the precautions were being relaxed and life was returning to normal. No-one could tell how long it would stay like that, but, I thought to myself, surely we have a year; let us make the best of it. The early part of the academic year 1938/39 went quite normally and even placidly. I took my Ph.D. in October and I busied myself with my official duties and with writing up some of the theoretical material in my thesis for publication. However, things were going on behind the scenes. Shortly after Munich, discussions began to take place between the senior staff of the Cavendish Laboratory, led by Cockcroft, and various high officials at the Air Ministry, including H. Tizard, D. R. Pye, and R. Watson-Watt, about how the research per­ sonnel of the Laboratory could best be used if war came. Visits were paid by a number of people from the Cavendish to government es­ tablishments where secret work was being done. These discussions led to the elaboration of a highly imaginative scheme whereby a significant number of qualified physicists were available for service immediately hostilities broke out. I knew nothing of what was going on until one day during June Ratcliffe buttonholed me in the Cavendish and asked me if I would be willing to take part in a scheme that Cockcroft was organizing under which a number of physicists from universities would spend five weeks during the Long Vacation on Air Force stations. Naturally, I agreed at once. There was an air of mystery about the communication and Ratcliffe did not tell me what the nature of the work would be, except that the object was to give us some training that would make us more useful in the event of war. A number of RAF stations were to be involved and each station was to have a group of scientists under a group leader. I was to be one of the group leaders. I heard nothing more until some weeks later, on Tuesday 19 July, my telephone rang late at night and a voice said “Cockcroft speaking. Can you be at the Air Ministry by 10.30 on Thursday morning?” I was not then as used to receiving such peremptory commands from Cockcroft as I later became. However, I pulled myself together and said that I would be there. It was, as I soon discovered, a meeting of group leaders to which I had been summoned. Besides Cockcroft, these included J. A. Ratcliffe,

War

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N. Feather, P. B. Moon, H. W. B. Skinner, C. E. Wynn-Williams, J. M. Nuttall, J. H. E. Griffiths, and P. I. Dee. Most if not all of these people were present. Watson-Watt was in the chair and he lost no time in letting us into the secret of radar and telling us of the existence of a chain of radar stations around the coast. It was on these stations that we were to work. Watson-Watt spoke with some pride and satisfaction. Indeed, he had every right to do so. While on the staff of the Radio Research Board, he was responsible for the initial experiments that demonstrated the technical practicability of radar and for the development work that had turned the idea into an accomplished fact. He was, at the time of the meeting, known in the Air Ministry as DCD which stood for Director of Communication Development, the use of the word “communication” being, of course, camouflage. The term radar was not adopted in the British services until towards the end of the war when standardization of nomenclature with the United States was agreed on. The British term was RDF which was a code name in that it was never expanded; in fact, the manual issued to the Chain stations began with the words “RDF is the name given to . . . ” I suppose that originally it stood for “range and direction finding”. Watson-Watt explained that the RAF personnel on the Chain stations had been very hard pressed and that one of the objects of the scheme was that we should take over some of the operating in order that they might have leave. To cover the period of 24 hours, three watches were required with three men in each watch. The idea was that, as soon as the group leader was satisfied that his group were competent, they should take over operating on alternate days. W. B. Lewis, who had been seconded from the Cavendish Laboratory to the Air Ministry on a full time basis from 1July, had suggested that it might be possible to give some of the groups technical work to do in addition to manning, and, as a result, it was decided to include a number of laboratory technicians in the groups. In fact, when we joined, war was imminent and all these plans came to nothing. The group leaders were put through a course of preliminary in­ doctrination which took a whole week, beginning on 14 August. We started with a visit of three days’ duration to Bawdsey Research Station located in Bawdsey Manor, near Felixstowe, where all radar research and development was concentrated. We afterwards visited Fighter Command at Stanmore, an RAF Group headquarters, and a Sector headquarters. The latter were both located at Biggin Hill, although they were operationally distinct. All the group leaders were present on these visits, except that A. C. B. Lovell came instead of Nuttall,

36

Memoirs o f a Computer Pioneer

and J. T. Randall came instead of Moon. Feather and Skinner, who disclaimed any particular knowledge of radio, brought K. Weekes and G. E. F. Fertel with them as their radio experts. Bawdsey Manor was situated in a secluded and charming spot on the east coast of England, just north of Felixstowe from which it could be reached by a ferry across the river Deben. The Superintendent was A. P. Rowe who had succeeded Watson-Watt about a year before when the latter moved to the Air Ministry. There were some 40 scientific and technical officers on the staff, along with a slightly larger number of assistants. Rowe’s principal experience had been admin­ istrative rather than scientific, but he had been present at the famous demonstration of the reflection of radio waves from an aircraft given by Watson-Watt and Wilkins in February 1935. The point that made most impression on me in his welcoming remarks, when he gave us a run-down of the work of the establishment and told us how our visit was to be organized, was a reference to the administrative frus­ trations which come the way of people in government service. These all arose, in his experience, from the form in which Treasury control was exercised. It was a sign of my own greenness that this classic complaint of those who serve the Crown in time of peace should have struck me as something new. It is fair to add that in war time the control was much relaxed and, at the level at which I worked, I rarely felt that I was fighting my own side. To anyone with knowledge of radio engineering, Bawdsey was an impressive place. The techniques there used for forming and shaping pulses were far beyond anything that I had been exposed to. Trans­ mitters, receivers, aerial systems, cathode ray displays and much more came into radar, and there was something of interest at Bawdsey in all these departments. Accurate measuring instruments were not in evidence, but the great drive was to get equipment working rather than to get scientific results. We saw a Chain station which, although it was located on the Bawdsey site and used to some extent for experiments, formed part of the operational Chain. Somehow, this station quietly working away seemed somewhat of an anticlimax after the other things that we had been shown and it was not until I had myself worked on a Chain station that I arrived at any true appreciation of radar in its operational role. Although Bawdsey Research Station was owned and run by the Air Ministry, a team of scientific officers from the Air Defence Experimental Establishment, which was an Army establishment, was working there on the application of radar to problems in gunnery. They were known

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as the Army Cell and had two projects. One of these, the development of an equipment with the code name GL intended to provide infor­ mation for the laying of anti-aircraft guns, had gone a long way and GL Mk I, which measured range and bearing but not elevation, was in production. This worked on a wavelength of about 5 metres. What made a much greater impact on me, however, was an apparatus known as CD that had been developed by W. S. Butement. This was built on a cliff overlooking the sea and the targets that it was intended to locate were not aircraft, but ships. It was, in fact, intended to provide the information required for directing the fire of coast defence guns. Several things were impressive about it. In the first place it worked on a wavelength of 1.5 metres. My amateur experience had made me familiar enough with 5 metres and I realized that on very short wavelengths conventional vacuum tubes no longer behaved in the straightforward way they did on longer wavelengths, the reason being that the transit time of the electrons becomes comparable with the period of the oscillation. I was therefore eager to go inside the trans­ mitter hut and see what sort of transmitter Butement was using. To my surprise, it was based on the use of conventional transmitting tubes and, except for the fact that the main tuning inductance was a single loop rather than a coil, there was nothing unusual about the circuit. The whole arrangement was, in fact, a modified GL transmitter, using similar tubes. The secret was to run the tubes at an anode voltage very much higher than that used in normal operation. This was possible without overheating the tubes because the pulse was very short; even though the peak power dissipated during the pulse was many times that dissipated in normal CW operation, the average power was very much less. The second thing that impressed me about the CD apparatus was that radar was here being used for precise measurement. Range was measured in yards rather than in miles and the relative bearing of two targets, measured by a split beam technique, could be determined to within a fraction of a degree. Unlike other things at Bawdsey which had already passed into the production stage, this project was still highly experimental. The information obtained from radar stations in the coastal Chain was not in suitable shape for passing direct to the Sector commander who controlled the fighter aircraft used for interceptions. A system known as filtering had therefore been devised. Readings from all the Chain stations were passed by telephone to Fighter Command where an operator plotted them by placing counters on a large table with a map painted on it. The filter officer’s job was to assess the reliability

38

Memoirs o f a Computer Pioneer

of individual plots, collate them with plots from adjoining stations, and pass on what it was hoped was reliable information to Group and Sector. All this we were shown in operation when we visited Fighter Command. We met H. Lamder who had contributed much to the development of these methods and who was attached to Fighter Com­ mand with a small group which became the prototype of the later RAF Operational Research Sections. We were escorted to Biggin Hill by Squadron Leader J. W. Gillan from the Air Ministry staff. It was not customary in those days for officers serving in Whitehall to wear uniform, and Gillan had some difficulty in establishing his identity. However, we were eventually admitted and shown the underground control room and other facilities. The Sector commander obligingly put some aircraft into the air and demonstrated an interception for our benefit. Gillan was an officer of great initiative and energy, who had distinguished himself the year before by flying the 327 miles from Tumhouse, near Edinburgh, to Northolt, near London, in 48 minutes. He played a significant role in the expansion and consolidation of the radar Chain during the early months of the war. He eventually returned to operational duty and was reported missing, presumed killed, in September 1941. The station to which I had been assigned with my group was Dunkirk, near Canterbury. Prior to the visit to Bawdsey, I had made a recon­ naissance of the area, partly to make contact in advance with the Flight Sergeant in charge and get an idea of the layout, and partly to find suitable accommodation for the party during the expected 5 weeks of duty. Bill Elliott and Charles L. Smith came with me and we were soon able to make arrangements for most of the party to stay at the Roper House Hotel in St Dunstan’s; others, with whom we were not in close touch at that time, made independent arrange­ ments to stay elsewhere in the city. Unfortunately, Elliott and Smith were not in the secret and I had to leave them outside when I went into the station. It may seem surprising that such an important command as that of a radar station, with much equipment either installed or being installed, should have been held by an NCO, but there could be no doubt about Flight Sergeant Phillips’ fitness for the job. I came to know him well later and admired his bearing under conditions of stress. Plenty was, in fact, going on that day, since the air manoeuvres of 8 to 11 August 1939 were in full swing. Everyone knew that when war broke out senior NCOs in command of Chain stations would eventually be com­ missioned; this, however, did not take place all at once and they lost

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their commands to young and inexperienced officers. Such is the way of the Service. The week immediately before starting at Dunkirk, I spent with my mother and father in Torquay. I drove there from Cambridge at a time when the news was getting worse every day. I bought a newspaper on the way and what I read in the stop press did not cheer me up. But so far we were still at peace, the weather was good, and the holiday was enjoyable. The night before I drove to Canterbury there was a display of fireworks. I stood watching it, wondering how long it would be before I saw fireworks again.

5 Experience on radar sites

On Monday morning, 28 August, the group assembled for the first time at the Dunkirk Chain station. We were all Cavendish men, although B. B. Kinsey and B. V. Bowden had taken their Ph.D. degrees a few years earlier and had left Cambridge. Kinsey was on the physics staff at Liverpool University. Bowden was a schoolmaster at Oundle and C. L. Smith, who had just taken his Ph.D., was going to join him there later in the year. It was not very usual then for people with such qualifications to teach in a boys’ school; whether it was inclination or lack of other opportunity that led them to do so, I do not know, but neither of them returned to school teaching after the war. We also had in the group R. Aves, a much respected and able technician on the Cavendish staff. The other members of the group, all research students, were: W. S. Elliott, whom I mentioned in the last chapter, T. H. T. Gant, J. H. Richards, and D. W. Millington. On the day that we arrived at Dunkirk, a detachment of light anti­ aircraft gunners also arrived and took up stations around the perimeter to give cover against attack from low-flying aircraft. Perhaps char­ acteristically, they arrived without ammunition, thus adding to Flight Sergeant Phillips’ cares and responsibilities, since it fell to him to obtain some through RAF channels. It was clear enough that we were not to have the uneventful five weeks of attachment to the station that had been originally planned. Fortunately, there was plenty for us to do. I passed on to the group the information that I had obtained about radar in its technical and operational aspects; we followed this up by studying the radar manual and other documents available on the station. It was a lovely summer and much of this study we were able to do out of doors. The equipment of the station was experimental and temporary. The receiver, it was true, had been built commercially to Bawdsey

Experience on radar sites

41

specifications, but it had been modified on the site. It was accom­ modated in a small crowded hut that was, at the same time, station headquarters. The receiving aerials consisted of a pair of crossed dipoles, mounted on the top of a wooden tower 24 feet high and connected by screened feeders to a radio-goniometer in the receiver console. Bearings were determined by rotating the goniometer until the echo received from the target aircraft was at a minimum. An approximate height was obtained by comparing the signal received from the dipoles at the top of the tower with the signal received from similar dipoles mounted lower down. The heights obtained were far from reliable and the problem of determining heights accurately was regarded as one for the future. The transmitter, which gave the impression of having been lashed up in the laboratory, was in a separate hut and was connected to an aerial on a second wooden tower through an open wire feeder. The wave-length was about 13 metres. The installation of permanent equipment was well under way. As an anti-jamming measure, this was to be capable of working on any one of four different wavelengths and a group of steel towers, 350 feet high, intended to support the transmitting aerials, had already been built. The existing wooden towers, of which there were in fact four, including the two already in use, would be used for the receiving aerials. We were shown the new transmitter in the course of erection. Its most notable feature was that it used demountable transmitting tubes whose filaments could be replaced when necessary on site. They were designed for continuous evacuation by diffusion pumps during operation. Those members of our party who customarily worked with vacuum equipment impressed Flight-Sergeant Phillips by immediately recognizing the pumps used. Erection of the transmitters had proceeded about half-way and it would be some time before commissioning could start. We kept ourselves quite busy during that first week as war came nearer and nearer. We repaired the transmitter once when it went wrong and we made arrangements to pay a fraternal visit to the Dover Chain station where Ratcliffe was in charge of a group. War became inevitable on the Friday when the Germans invaded Poland. I heard Mr Chamberlain’s speech on the morning of Sunday 3 September in the private hotel where I was staying. While he was still speaking, the first air raid warning of the war was sounded. The proprietor of the hotel was a senior air raid warden and the hotel was the post from which he operated. There was soon much activity as wardens reported for duty and members of the public came in with various troubles. One messenger came, I remember, from a family that had omitted

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to obtain its respirators and I wrote out a chit to the depot requesting their issue and got the senior warden to sign it. This certainly sent the applicant away happy, but whether he got his respirators at that time I do not know. When the all-clear was sounded, the senior warden thought that it would help to allay anxiety if he sent out a patrol to make a circuit of the area. It must have had the opposite effect. I have never seen anything more alarming in my life than the sight of two people, one tall and one short, dressed in gumboots, gas capes, and protective headgear parading along the street carrying respirators, on that hot Sunday morning. However, in due course they arrived back and reported that all was well. All, indeed, would have been well if one of them had not put on over her shoes a pair of gumboots that were slightly too small. Getting those gumboots off called for the application of some force and the poor girl was lucky not to lose her leg. When the all-clear had sounded we lost no time in getting to the RAF station where we found everyone discussing the cause of the false alarm, for that was what it was. However, our thoughts were more on the attack that we assumed would be coming soon. Perhaps we exaggerated our importance in the scheme of air defence, but we thought it not impossible that the enemy would take a look at us before going on to more important targets. Wishing to be at the scene of action so as to be available to give help if necessary, some of us went back to the station after dinner. The troops were a little surprised to see us, but it was obvious that they appreciated the kind thought. On a normal night, the operators were kept quite busy since, even in those days, there was a good deal of flying around the south coast and there were always the regular civilian aircraft flying between the continent and London. That night, however, there was nothing, not a “blip”, as the parlance went, to be seen on the tube, only echoes from the balloon barrage then flying behind us to remind us that we were at war. As the night went on, we realized that we were doing no good and with mixed feelings of relief and anticlimax we headed back to Canterbury. Roper House Hotel had changed somewhat during the last few days. It had been partly taken over as the Officers’ Mess of the Green Howards, a local unit of the Territorial Army. No doubt because of our official connections, we were allowed to retain our table in the dining room and were waited on by soldiers. The other residents of Roper House, mostly old ladies, were accommodated elsewhere. It was a pity that we did not get to know any of the officers, since we were as curious about them as they no doubt were about us.

Experience on radar sites

43

Declaration of war had cleared the air to the extent that we could not now expect to return to our universides at the beginning of October as planned. I must have been in touch with Cockcroft, for in a letter dated 5 September, I said that I was glad that he was taking up the matter of our future work. At some point he mentioned that there might be a requirement for people to take radar equipment to France. At least two of the group volunteered for this duty but, as far as I know, nothing came of it. However, none of us had to wait very long before work was found for us to do. I was one of the first; in the week after the outbreak of war I found myself, having handed over my responsibilities such as they were to Kinsey, back in Cambridge engaged in what must have been as remarkable a piece of scientific improvisation as any ever undertaken in the furtherance of war. Cockcroft himself had taken a party to Bawdsey consisting of E. S. Shire, R. Latham, J. Ashmead, A. E. Kempton, C. W. Oatley, and E. G. T. Morley. Oatley was a former Cavendish man, then a lecturer in Physics at King’s College, London. Morley was one of the Cavendish Laboratory technicians. This group had gone to Bawdsey with the two-fold intention of studying the Army equipment under development and of working on the RAF Chain station. Cockcroft had, I believe, already been booked to work in the Directorate of Scientific Research at the Ministry of Supply (this being the procurement department for the Army, the Navy and the Air Force having their own procurement organisations) in the event of war. This is what he eventually did and the whole of the group with him at Bawdsey settled down in various jobs connected with radar in the Army. When Cockcroft and his group reported at Bawdsey on 28 August, they found the establishment—which I will from now on refer to as TRE, although it did not in fact acquire that name until 1942—packing up ready for evacuation to Dundee. A. P. Rowe, in his book “One story of radar”, has told the story of this event; how they arrived at Dundee to find that the accommodation that they expected to occupy was not available and how they were finally fixed up with a floor and a half in a Dundee Training College. I saw them in their misery some time during November. Butement had departed for duty at the Ministry of Supply, leaving behind him his experimental CD set with, fortunately, someone who knew how to switch it on. The group thus found itself ideally placed to become thoroughly familiar with a system from which many significant radar developments were to spring. One of these was the establishment round the coast of a chain of 150 centimetre radar stations, known as CHL stations, designed to supplement the main Chain. CHL stations would not be capable of detecting high

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flying aircraft at such great distances as the main Chain stations, but they would, by virtue of their much shorter wavelength, give better cover against low flying aircraft. Cockcroft was not given, even before the war, to staying long in one place and at this period he was here, there, and everywhere, attending meetings and making contacts. Oatley has told me how one day Cockcroft arrived back from a meeting and said in his quiet way that Watson-Watt had pushed across the table to him a piece of paper on which was written “Can you make some CD sets?” He had agreed to do this and he set about mobilizing his troops, which included myself as well as the other people I have mentioned. The idea was that we should construct the sets with such resources as we could acquire on a crash basis, quite independently of longer term plans. The operational role for which the equipment was intended was connected with defence against U-boats. One of the ways for U-boats to reach the Atlantic from German ports was to pass through the Fair Isle channel between the north of Scotland and the Shetlands. This they did on the surface and it was thought that four CD stations suitably sited, two on Fair Isle, one at Sumburgh in Shetland, and one on the Scottish mainland, would enable their passage to be detected. For this reason the stations were given the name CDU. The detection of low flying aircraft was, in the original concept, a subsidiary role, although it assumed great importance later. The Cavendish Laboratory was the obvious place in which to con­ struct the receivers and, on or about 9 September, a party left Bawdsey in a van loaded with components from the Bawsdey stores. How they persuaded the storekeeper to part with these components I do not know; certainly, it was many years before the accounting problems posed thereby were finally cleared up, if, indeed, they ever have been. Everything that we did was irregular by normal service standards. Wherever we went, we must have caused consternation and chaos. However, we were not altogether to be blamed for this. The leading spirits behind the enterprise were Vice-Admiral Sir James Somerville and Air Marshal Sir Phillippe Joubert. Somerville had been brought out of a premature retirement into which ill health had driven him and installed in the Admiralty with some such title as Director of AntiSubmarine Weapons and Devices. Joubert was at the Air Ministry. Both were dynamic personalities and by their rank and position could ensure that full co-operation was forthcoming, whatever the rule book might say. Somerville in particular rather enjoyed showing a little of the Nelson spirit.

Experience on radar sites

45

And so I found myself back in Cambridge sharing a room in St. John’s College with Oatley. Shire was also in our party and our job was to produce the receivers. Kempton, Ashmead, and Latham had gone elsewhere to work on the transmitters. The first thing that Cockcroft did was to take Oatley and me with him to call on Pye Radio who were already involved in the official CHL programme. They were helpful and undertook to produce the receiver rack with the cathode ray tube in position and provided with the necessary power supplies and deflection amplifiers. They also undertook to supply the receiver which followed closely Butement’s design. It consisted of two radio frequency amplifiers with sliding tuners and acorn tubes. These amplifiers were followed by a frequency changer which fed an I.F. strip operating on 45 megacycles. This I.F. strip was straight out of a Pye television receiver where it formed the radio frequency amplifier. When television transmissions started in London in 1936, there was little likelihood of a second channel be­ coming available in the near future, and it was possible to use a straight RF amplifier instead of a superhetrodyne. It was an enormous piece of good fortune that this amplifier was in production at the outbreak of war; I do not know where we would have been without it. It had just the right bandwidth and gain for radar purposes, and was pressed into service for many applications. I was rather disappointed that Pye should undertake such a large part of the constructional work; however, there was still plenty left for us to do. I was responsible for the time base and for the calibrator which, when switched in, would produce range marks at 10 mile intervals. The time came when the prototype was ready to take to the Air Defence Experimental Establishment (ADEE) for mating up with the transmitter that Kempton and Latham were working on. This estab­ lishment had been for many years located at Biggin Hill, but a move to Christchurch had been planned to take place late in 1939 or early in 1940; on the outbreak of war the Ministry of Supply Staff working at Bawdsey were forced to move to Christchurch at once, although the new buildings were far from ready, and they had to camp out as best they could. The main move from Biggin Hill took place some months later. I drove down to Christchurch with some aerials strapped to my car. In Cambridge we had been working long hours in order to do the job as soon as possible, and I was somewhat shocked to find when I arrived in Christchurch that the establishment was still working peacetime hours, which meant that scientific officers started at about

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9 o’clock in the morning and went home at about 4.15 in the afternoon, while assistants arrived slightly earlier and left later. However, they had some excuse in the primitive nature of the working conditions. The main site of the establishment was at Somerford, a few miles east of Christchurch. Nearby was a small wooded promontory known as Steamer Point where the cliffs were about 50 feet high. This was ideal for experimental work with CD equipment. A narrow strip of land had been fenced off and a small laboratory built. It was here that our experimental equipment was set up and we found ourselves working alongside the regular staff engaged on the long-term pro­ gramme. Later on, Steamer Point became a comfortable and convenient place in which to work. It was far from that when I first saw it. The only power supply was from a portable diesel generator of a type that I came later to know very well, along with the slightly sweet smell of burnt dieselite. The permanent road along the cliffs had not yet been constructed and everywhere there was mud. A good pair of gumboots was essential equipment. War and mud seem to go together and if we did not have our baptism of fire, we certainly had our baptism of mud. A CDU station consisted of two wooden huts about 12 feet square and sited some 25 yards apart. One contained the transmitter and the other the receiver. Straddling each hut was a heavy wooden gantry supporting a platform on which was mounted a turntable carrying an aerial array. Transmitting and receiving aerials were similar and con­ sisted of 16 half-wave dipoles mounted in two vertical stacks of four each. Behind these, about 30 inches away, was a reflecting screen of wire netting. The transmitter was connected to its array through open wire feeders with matching sections arranged in such a way that the dipoles were energized in phase. The receiver was similarly connected, except that coaxial feeders with polythene insulation were used and a mechanical switch for beam switching was mounted near to the array and rotated with it. Much of all this followed the design evolved for the regular CHL programme to which I have referred. The turntables, however, were of the type used in GL equipment to carry a small rotating cabin to which aerials were attached. For our application, we mounted them upsidedown on the gantries. It was necessary to be able to turn the aerials from inside the cabin and here the true spirit of Cavendish improvization found full scope. I suspect that Shire was the leader in this. The turning mechanism inside the cabin was made from an old bicycle with the pedals replaced by a pair of wooden handles. The frame was cut down and screwed to the ground so that the handles were at a convenient height for an operator. A long length

Experience on radar sites

47

of bicycle chain was passed through the roof and conveyed the drive to a sprocket wheel attached to the turntable. In practice this bizarre device was remarkably successful. It was necessary that the transmitting and receiving arrays should always point in the same direction. Ac­ cordingly, potentiometers were mounted on the two turntables and a galvanometer of the kind used in the elementary physics laboratory was mounted in the transmitting cabin just in front of the turning mechanism. In operation, the receiving aerial was rotated by an op­ erator as he searched for and subsequently followed targets. Another operator in the transmitter cabin turned his handles so that the gal­ vanometer pointer was kept as nearly as possible at zero. The RAF have a term for boring and uninspiring work; they call it binding and the man who worked the transmitting aerial was always known as the binder. Late in September Ratcliffe made a reconnaissance of the islands looking for likely sites and making arrangements for a supply of oil for generators and for other unwarlike stores. He did this to the great satisfaction of Admiral Somerville, who voted him, according to Cock­ croft, as being worth “a guinea a minute”. Plans were all going smoothly when, on the night of 13/14 October the German submarine U47 penetrated into the anchorage at Scapa Flow and torpedoed the Royal Oak which was sunk with heavy loss of life. The fleet instandy dispersed to other anchorages and when, on 17 October, enemy aircraft raided Scapa they found no ships to attack except the old Iron Duke, then in use as a depot ship. A large part of the fleet went to the Firth of Forth where shortly after arrival it was attacked from the air. The need for protection against low-flying aircraft approaching from across the North Sea was now very necessary and the decision was taken at high level to erect one of the CDU stations on the May Island in the Firth of Forth instead of sending it further north. Cockcroft assigned the task of erecting the station to a group consisting of myself, Latham, and Fertel. We were joined by Clifford Evans who, along with three other Cambridge men, had been commissioned into the Royal Naval Volunteer Reserve with a view to taking command of the stations when erected. By about 20 October the equipment was ready to be packed into army trucks and sent up to Edinburgh. We were to follow on the night train on 21 October. ADEE, like other army establishments, was under the formal com­ mand of a military commandant, although the scientific staff came under a civilian superintendent who was responsible for their work. The commandant at that time was Lt. Col. W. H. J. Costelloe. He was facing his share of the problems created by the irregular way in

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which Cockcroft’s group was being handled. He had already, with dubious legality, drawn on his imprest account to the extent of £1,500 to pay a contractor who had delivered some cabins and towers required by Cockcroft, and he felt obliged to make cash advances to people like myself who were not yet regularly appointed. He addressed a strongly worded minute to headquarters in which he protested that it was quite impossible to go on running the establishment in the way that he was being forced to do. This, however, did not prevent him from doing everything in his power to help. He sent for me on the morning of my departure to wish me well in the mission on which I was embarking. He may have been somewhat envious, since I am quite sure he would have liked to be on more active duty himself. One deficiency he could and did rectify. I had no written authority and no uniform, and he therefore had typed on official paper a doc­ ument stating who I was and what I was doing. This got me out of a difficulty a few days later when I was challenged by a security guard in Leith docks. Ratcliffe joined the party in London and we travelled up to Edinburgh together. I was not expecting that Ratcliffe would be with us and it appears that Cockcroft asked him at the last moment, without, in fact, clearing the matter with the Superintendent of TRE to which estab­ lishment Ratcliffe was by then attached. After about a week TRE tracked him down and he left us abruptly. There was, to begin with, some confusion because the equipment had been sent addressed to Admiral Somerville at Leith docks. Since Admiral Somerville was in London and since Leith docks spread over a wide area this was a somewhat imprecise address. Oatley had re­ mained in Christchurch and he recalls that I sent him a telegram saying “Please do not address things to Leith docks; they are five miles long”. However, we soon got in touch with the right officer. He was in fact expecting us, having received what he described as a “comic signal” —meaning one he did not understand—from the Admiralty. Landing gear on the May Island was no straightforward matter as we soon discovered when we went there on a visit. Only a very small vessel could approach the landing place and the wind and tide had to be exactly right. However, the Naval Transport Officer at Leith was able to locate a small vessel whose skipper thought that he could do the job, and the equipment was soon loaded. It was then necessary to wait for favourable weather conditions. We waited, I think about ten days, and then the blow fell. On 4 November the weather was right, but the crew were far from right; it was Saturday night and they were all drunk. The news reached

Experience on radar sites

49

London before it reached us, and things began to happen rapidly. The decision was taken to abandon the proposal to erect the station on the May Island, and to erect it instead on the Fife coast. I received instructions to go there at once and pick a suitable site. As I crossed the Forth Bridge in the train I looked down on the beautiful sight of battleships riding at anchor in the estuary, a sight that gave some meaning to the mission on which I was engaged. A naval car met me at Inverkeithing. I called at the dockyard at Rosyth to borrow a map; they had no such thing, but obligingly fixed me up with an Admiralty chart which fortunately showed the roads and contours along the coast. It was a cold and wet afternoon and it was some time before I found what I wanted. Eventually I settled on a site between Anstruther and Crail that had the required properties. It overlooked the cliffs, it was level and flat, and had good access from the main road. I noted the exact location on the chart and returned to Rosyth. With great speed the site was requisitioned and arrangements made to do the necessary work on it. Meanwhile Cockcroft had been conferring with Somerville and Gillan in London and took the night train to Edinburgh on Tuesday 7 November. He had breakfast with me the following morning at my hotel before going on to see the Commander-in-Chief at Rosyth. The materials for the huts and gantries were soon delivered to the site. In addition to the huts housing the transmitter and receiver, there was a long hut divided up so as to provide living accommodation for the personnel and a small administrative office. Before going back to London, Cockcroft spent part of one day with us on the site. As we watched the erection going forward, he remarked that he had been engaged in erecting huts during the First World War. Cockcroft was not given to saying more than was necessary and this is one of the few occasions on which I remember his volunteering information about his own life. It was typical of him to give me the impression that his service in the First World War had consisted mainly in erecting huts and such like; in fact, he had served with distinction as a signals officer and had been twice mentioned in dispatches. Once the gantries were erected and the equipment installed in the huts, the job of lining up the aerials and getting the station into operation could begin. By this time Evans had under him a naval detachment who were eventually to be trained as operators, but who in the meanwhile provided some very necessary assistance with the mechanical work. Latham and Fertel took full responsibility for the installation of the transmitter and, when they were satisfied with it, rushed off for other work connected with the CDU programme.

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By 17 November, we were ready to carry out trials with cooperating aircraft. These were heady times for young men who felt the weight of their responsibilities and were anxious to show what they could do. Evans and I drove ourselves hard, and, during the period when we were working the station up and training the operators, we hardly left the site except to snatch some food. The military initiative lay with the enemy at this stage of the war and he had embarked on a campaign of laying magnetic mines by aircraft in the Thames estuary. This led to a further diversion of two of the CDU stations to Foreness and Walton-on-Naze respectively, and to Cockcroft’s being commissioned to make two more. Eventually a station was erected at Sumburgh Head in Shetland and two were erected on Fair Isle; the original plan was thus implemented, but to the extent of three stations instead of four. The bill from the University of Cambridge for the work done in the Cavendish Laboratory on the six stations amounted to just under f 1,000. Nothing very exciting happened operationally during the time that I spent at Anstruther. The equipment worked well and we had very little trouble with it. The same was not true of the cooking stove in the troops’ quarters. The oven failed to reach the proper cooking temperature as a result, it was afterwards discovered, of having been assembled wrongly. Evans tells the seemingly unlikely—but, he asserts, biologically sound—story that on one occasion the cook tried putting the meat in overnight and getting the guard to stoke the fire at regular intervals during the night. By the following mid-day the meat, still not cooked, was beginning to go bad. When we first reconnoitred the area we made enquiries of one of the naval officers from the May Island as to a good place to stay, and were told that “you could get a very good doss down at the Commercial Hotel, Anstruther”. In fact, it was the most comfortable and welcoming place that one could imagine. Shortages had not yet developed and I remember in particular the Scottish high tea in its full glory. By the latter part of December the station was running smoothly under Evans’ command and I could relax. I was looking forward to the special fare promised us for Christmas. However, in the event I spent Christmas under very different circumstances. I suddenly received a telephone call from Cockcroft; I was to go at once to one of a second group of stations that were being erected with great urgency. These were not part of the CDU programme, but were early stations in the planned CHL chain. The one that I was to go to was at Shotton not far from Durham.

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51

I left Anstruther on Thursday 21 December and put up that night in a hotel in West Hartlepool. Next morning I armed myself with a map and set out towards the north in a crowded bus. The station, when I finally located it, turned out to be on a dreary piece of high ground about three miles from the coast and nine miles east of Durham. When I revisited the area many years afterwards I could recognize very little, it being all but overrun by the new town of Peterlee. No-one was at home when I arrived at the site, save for a gang of riggers who were working on the aerial gantries. However, before very long Cockcroft turned up with Ashmead and one of the Cavendish Laboratory assistants and, after a brief inspection, we repaired to Durham where we put up in a hotel for the night. Next day we went back and proceeded to make our number with the parent RAF station. We had some general talk and then went to the site with Warrant Officer E. Swinney, who was to be in charge. Cockcroft had again shown his power over men by the way in which, with no difficulty at all, he had obtained possession of a set of tools that were being held for the station. This somewhat disconcerted Warrant Officer Swinney who had been letting them stay where he thought they would be safe. He did, however, show a certain grudging admiration for the way it had been done. It soon became clear that work was coming to a standstill on account of the lack of the aerial frames which had been sent by rail, but which were not to be found at the nearest railway station. This situation suited the riggers who were all set to go home for Christmas. Cockcroft, however, was not deceived and it did not take him long to locate the missing aerial frames at another station just down the line. Ashmead and I both felt that the wisest course would have been to let the riggers go, but Cockcroft was adamant in insisting that the work should go on. The enemy was making a good thing out of his tiresome practice of dropping magnetic mines in the mouths of the rivers round the coast, and Cockcroft said he was under orders from the Air Ministry to brook no delay in getting the station going. What he said to the foreman of the gang I do not know but, good chaps that they were, they took it well. Some of them had bought turkeys and chickens to take home to their wives and I felt very sorry for them. Ashmead and I continued to live at the hotel in Durham. Our Christmas dinner consisted of a mixed grill; a little later in the war this would have been luxury indeed, but at that time it seemed rather on the thin side. The receiver, which was my particular province, Ashmead looking after the transmitter, was made by Pye Radio who had sent up a

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young engineer with it. It was a simplified version of what was to be the production model. It worked very well except for the time base which was a primitive affair compared with the one that I had built for the CDU stations. I solved the problem by having the circuit modified to conform to the one I had used. The modification was entirely successful and I had the satisfaction of hearing the details dictated over the telephone by the Pye engineer to a colleague on another station where they were having similar difficulties. The calibrator was also a much simpler device than the one I had designed, but here I had to admit that it worked very well and was quite accurate enough for the purpose. We soon had the station on the air and by the end of the week our presence was no longer needed. Ashmead reported on the tele­ phone to Cockcroft and negotiated a week’s leave. I was quite exhausted after a week of long and irregular hours. Nevertheless I was anxious not to waste any of my precious leave and set off late in the afternoon for my home in Worcestershire. I arrived at York in the early hours of the morning and had had quite enough; I found my way in the blackout, as much by sense of touch as anything else, to the station hotel—although it would have been hard to miss so enormous a building—where the night porter gave me a room and I was soon fast asleep. When I reported at Christchurch after my leave I assumed that my temporary involvement with the operational aspects of air defence was over and I expected to settle down as a normal member of the staff of ADEE and to work on army radar. There was however to be one more interlude. I was summoned to attend a somewhat highlevel meeting in London concerned with the remainder of the CHL stations that were being erected under the crash programme that Cockcroft was running. Apart from Cockcroft and myself, Watson Watt was present and so was Rowe. As a result of this meeting, it was decided that I should proceed to Cambridge to check out the receivers as they came off the production line at Pye. I very much enjoyed the week or two back in Cambridge. The University was, I found, little changed except for the Cavendish Lab­ oratory, where nearly all the staff and research students had left to do the sort of work that I was doing. I spent some time with Kenneth Craik who was fast being involved by Bartlett in serious work for the services. At the beginning of February I was sent on to Ingoldmels, near Skegness, where a CHL station was being erected on a low site just behind the sea wall. Up to this point I had seen little of the confusion

Experience on radar sites

53

of war. Cockcroft’s purposefulness and the steadiness of the regular RAF officers and NCOs concerned carried everything along. Here things were a little different. I was met at the station by Fit. Lt. N. V. Webber, a capable officer with an M.C. from the First World War, who had recently been commissioned in the R.A.F. and who was a radio communication engineer by profession. When he heard that I was attached to the Ministry of Supply he said that supply was what they needed. We had to go in a taxi to the station since he had no transport. His troops consisted of airmen recently joined like himself and not yet fully kitted out; I remember one tall young bank clerk still wearing his own clothes, no uniform having so far been found to fit him. There were no NCOs when I arrived and, whatever other deficiencies there were, acting unpaid stripes were soon to be in good supply. The confusion extended to the technical side. The receiver had been connected up, but there were alarming symptoms when it was switched on and it was discovered that lack of experience with three-phase electricity had led to its having 346 volts applied instead of 200. Fortunately it survived this experience without too much dam­ age being done. By this time the official RAF organization was beginning to operate and Cockcroft’s group of irregulars were becoming redundant. In particular, TRE were anxious to assume their rightful responsibilities and, in fact, had a representative on the site. My position was, therefore, for the first time ambiguous although in no way embarrassingly so. I had some indication of what was going on when one of Gillan’s officers from the Air Ministry spoke to me on the telephone and said that they were looking to me to get things going, only to ring again a few minutes later to say that he had exceeded his instructions and that it was really the man from TRE who was responsible. The matter was ventilated at a meeting held in Dundee on 12 February at which TRE made it clear that they could now do their own work. By 14 February I was on my way back to Christchurch and my association with the RAF had, for the time being, come to an end.

6 The A ir Defence E xperim ental Establishment

At Christchurch I was put to work under C. W. Oatley, and as time went on I began to have some feel for the character of the Estab­ lishment. It had started during the First World War as a Royal Engineer Experimental Section at Woolwich, and at the end of that War had become a civilian establishment under the War Office, with the name Searchlight Experimental Establishment. In 1924 it was renamed the Air Defence Experimental Establishment (ADEE). In addition to searchlights, the Establishment acquired responsibility for artillery sound ranging and for that new technical marvel, the anti-aircraft sound locator. The buildings at Christchurch had been planned very much with searchlights and sound locator research in mind and one felt that the realization that the sound locator was out of date had yet to come. At the time I joined the ADEE experiments were going on with a view to fitting a cathode ray tube indicator to the Mark IX sound locator. This would give the operator a visual indication of the position of the target instead of an aural indication. A sociologist would have found it interesting to study the effect on this closed community of the return of members of the Army Cell from Bawdsey and the simultaneous arrival of a bunch of outsiders from the Universities. The latter must have seemed insufferable in their self-assurance and in their lack of respect for official channels. In retrospect, I have much sympathy for the permanent staff. Oatley had taken part in the construction of the CDU sets in Cam­ bridge, but had been prevented by a sharp attack of influenza from going into the field with them. It therefore came about that he joined the Establishment at Christchurch well before the rest of us. He saw the long-term importance of establishing good relations with the regular people and by the time I joined him had succeeded in gaining some measure of trust from D. H. Black, the Superintendent, and from H.

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W. Forshaw, the Principal Scientific Officer. By then working conditions were tolerable, if not ideal. Oatley told me that, when he set up his group to work on receivers, he had had to make a forage into Bourne­ mouth to buy the basic tools necessary for work to proceed at all. I leamt a great deal from Oatley, both during the period we were at Cambridge together and during this period at Christchurch. When I arrived, a project entirely manned by the ex-CDU group was being set up with the object of repeating, and improving on, the success that Butement had achieved on 150 centimetres by doing the same on 50 centimetres. For ships or low flying aircraft the shorter the wavelength the better and it was felt that 50 centimetres would be a great improvement on 150 centimetres. My job again was to work on the receiver. This boiled down to making a frequency changer since the rest of the equipment, including the IF amplifier, the time base, and the display, could be taken over from earlier work. There was no possibility at that time of obtaining effective radio frequency amplification on 50 centimetres and Oatley suggested that I should construct a diode frequency changer using a miniature thermionic diode. There was very little to go on by way of published work, but Oatley showed me one paper that had recently appeared in the Wireless Engineer. I soon discovered, however, that the operating conditions assumed by this author were not those that gave the best signal-noise ratio, but were those that made the mathematical calculations possible. This confirmed me in my healthy scepticism of mathematical analyses that purport to apply to practical situations. I do not remember much about the transmitter, but I do remember that the aerial system consisted of arrays of dipoles in front of a wire­ netting reflector. It was, in fact, a scaled-down version of that used by Butement. Both transmitter and receiver arrays could be accom­ modated on the same turntable. Shire designed a capacitadvely coupled switch for forming the split beam used to determine the bearing of the target. He sent off sketches to the Cavendish Laboratory where the switch was made. By March 1940, the equipment was working and we began to get echoes from targets. We obtained detection ranges of about 35 miles on aircraft and about 5,000 yards on the Titlark, a small pleasure vessel that had been taken over for use as an experimental target. By June, with bigger arrays, better feeders, and Micropup transmitting tubes, we were getting 8,000 yards on the Titlark. At this point we felt that we had achieved all that was possible without some significant

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breakthrough in receiver or transmitter design and that we had the basis of a successful design. However, we had a competitor. From the beginning it had been realized that there would be great advantages in working on wavelengths around or below 10 cendmetres. Oliphant saw this very clearly, and soon after the outbreak of war, he returned with members of his group from the Ventnor Chain station, where they had been attached, to Birmingham University to make a serious attack on the problem of generating power on centimetric wavelengths. Effort was concentrated on the klystron, a device that had been described in the literature a few years earlier. However, J. T. Randall and H. A. H. Boot were, in response to their urgent representations, allowed to try out an idea of their own which they felt would combine the advantages of the klystron and the magnetron. Their success was immediate and spectacular, and soon the entire effort of the group was switched to the development of the cavity magnetron, as the new device was called. Early in April a magnetron was reported as giving 100 watts at 10 centimetres and a month later a continuous power of 1 kilowatt was being obtained on 8 centimetres. Progress continued to be made. I was not myself at all well-informed about what was going on. The first time I saw any centimetric equip­ ment in operation was on a visit to Worth Matravers, near Swanage, where TRE had moved in May 1940 after its uncomfortable period at Dundee. What I saw was a very primitive experimental set-up and I remember wondering whether the work could possibly have any bearing on the present war; had I been better informed I would not have had those doubts. It was on the RDF Applications Committee of the Scientific Advisory Council that the battle with 50 centimetres was fought out. Appleton, the chairman, remarked at a meeting of the Committee held on 17 October that the 50 centimetre development at ADEE did not seem to be any further advanced than the shorter wave work at Birmingham and TRE. Black disagreed, and after a long discussion it was decided to postpone a decision as to whether the 50 centimetre work should be discontinued until another meeting at the end of October. When this decision eventually went against us we were naturally very dis­ appointed, but, in retrospect, it seems to have been a fortunate one. 50 centimetres is an awkward wavelength which is neither one thing nor the other, and the decision not to proceed with it meant that more effort would be available later for the development and pro­ duction of 10 centimetre equipment.

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In due course, the use of centimetric wavelengths was to change the picture entirely, but at the beginning of 1940 it was obvious that radar at its existing stage of development could be applied much more effectively to the problems of the RAF than to those of the Army. I was quite clear that, if I were to be allowed any choice in the matter, I would prefer to work on projects that were likely to be of immediate use in the prosecution of the war rather than on long-term research. Consequently I was not very happy about the prospect of continuing to work at ADEE and I therefore wrote to Ratcliffe asking whether he could do anything to get me transferred to TRE. He sent me an encouraging reply and a short while afterwards Cockcroft spoke to me on the matter. Nothing happened, however, and I did not pursue it further. This was partly because, just when the first exciting phase of the 50 centimetre work was over, I had an opportunity to join a group led by Captain Hugh Young, the function of which was to carry out trials on newly developed equipment. This was a good deal nearer to operations than working in a laboratory. Young, who held a com­ mission in the Territorial Army, was a member of the peace time scientific staff of the establishment and had gone out of his way to be helpful to greenhorns like myself. He was shortly to leave the ADEE to take up a post as a serving officer in Branch A5 of the Ministry of Supply, where I was to have a good deal to do with him later on. While the events that I have described were taking place in our small world, other events of wider importance were taking place across the Channel. On the outbreak of war the enemy had lost no time in beginning an all-out attack on allied shipping and this fact was brought home to the public by the starting of meat rationing on 6 February. Land fighting had, however, been slow to develop and on 25 January Chamberlain was assuring the House of Commons that we were right to drop leaflets instead of bombs on Germany. When events began to move they moved rapidly. On 10 March the Finns capitulated to Russia. On 2 May Chamberlain reported the evacuation of south Nor­ way and faced a censure debate in the House. On 10 May Churchill became Prime Minister. At dawn that morning the Germans had launched their assault on the Low Countries. On 19 May, during the course of his first broadcast as Prime Minister, Churchill announced that the Germans had broken the French defences north of the Maginot Line. “It would be foolish to disguise the gravity of the hour”. In France, Reynaud, already Premier, had taken over the Ministry of National Defence and Petain, the defender of Verdun and now aged 84, had been recalled from the French Embassy in Madrid to be Vice

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Premier. By 21 May the enemy had crossed the Meuse and Reynaud, speaking in the Senate, had said, “The country is in danger. My first duty is to tell the truth.... I believe in miracles because I believe in France”. Weygand, aged 74, had taken over as Commander-in-Chief of Allied Forces in France. The enemy drive towards the channel ports gathered force. By 24 May the capture of Toumain was claimed and British troops were withdrawn from Boulogne in the face of the advancing Germans. Next day the situation was officially described as “grave; no reason to lose confidence”. A few bombs had already fallen on England and the first civilian casualties of the war had been incurred. By 29 May Belgium had been overrun and the British expeditionary force was falling back on the coast. The evacuation of British troops from France began and the Christchurch area, where I was, began to fill up with French troops who had been evacuated along with them. By 1 June the evacuation from Dunkirk was almost over and Field Marshall Lord Gort was ordered to hand over his command to a less senior officer and, on his return to England, was created Knight Grand Cross of the Order of the Bath. Three days later Churchill speaking in the House found it necessary to say, “We must not assign to this deliverance the attributes of a victory”. By 14 June the Germans had entered Paris, which had been declared an open city, and a few days later the French requested an armistice. We then knew that we were on our own. My first assignment with the trials group took me back to 150 centimetres. The General Staff had laid down a requirement for an equipment working on this wavelength that would be capable of pro­ viding sufficiently accurate measurements of range and bearing for the control of the fire of coast artillery guns. There were some doubts about whether the desired accuracy of bearing could be attained. In particular, it had been suggested that the presence of the guns —a large mass of metal—in the vicinity of the antennae would have an adverse effect. Accordingly, a CHL station had been erected at Culver on the Isle of Wight for the purpose of conducting trials. It was also important to determine the range of the equipment on small craft such as motor torpedo boats. The trials were to be conducted jointly with the Coast and Anti-Aircraft Defence Experimental Establishment (CAEE) and I was thus, for the first time, brought into contact with an establishment that I afterwards got to know very well. Culver Fort had been established in Napoleonic times and the original buildings were still in use. It had at one time mounted 7 inch rifled muzzle loaders, and emplacements for these interesting guns, together with name plates on the walls, still existed, although the guns themselves

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had long since disappeared. The current armament was a battery of two 9.2 inch guns. The headquarters of CAEE and the Officers’ Mess were in Bembridge Fort, another fort of the Napoleonic era, a short distance away. There was something pleasantly old-world about these surroundings. CAEE had originated in 1935 as an experimental section under the Fire Commander at Culver and had become an independent Estab­ lishment in 1937. It was commanded by Lt. Col. C. L. Ferrard, M.C., a gunner of the old school. He was slightly peppery but could be extremely nice. The arrangements he made were not always entirely optimal. For example, one day he set a gunner to colour a chart, but, since the gunner unfortunately happened to be colour blind, the Colonel had to stand by him to tell him which crayons to use. The establishment was entirely military in composition and there were three or four officers responsible for carrying out the trials. The ones I worked with most closely were Lieutenant J. A. Ramsay, a Cambridge zoologist slightly senior to myself, and Captain N. Carter, a regular gunner officer. There was also Captain the Hon. John Benson, son of the first Lord Chamwood, whom he was eventually to succeed. John had an expansive personality, combined with an acute and en­ quiring mind and an absorbing interest in both things and people. He held a commission in the Territorial Army and on the outbreak of war had gone to France with his regiment. The evacuation through Dunkirk had exacerbated an old trouble with one of his hips, and left him with a limp. This in no way diminished his zest for life. I was not the only one to come to value his friendship and to enjoy his compulsive hospitality. Other officers whom I got to know at CAEE were Lieutenant J. Vint, M.C., a First World War veteran who in peace time was a lecturer in mathematics at Bristol University, and Lieutenant Paul Dykes, a Cambridge engineer of about the same age as Ramsay and myself. The trials at Culver proved interesting and, when I made my report in the middle of July, I recommended that a mobile set should be constructed in order that further trials might be conducted on a wide variety of sites. I was particularly concerned about the effect of fixed echoes from high land along the coast or behind the site. The trans­ mitting and receiving aerials then in use were not sufficiendy directional to cut out such echoes completely, even when looking out to sea. The main hope was that it would be practicable to choose sites at which fixed echoes were not very strong; hence the need for more siting trials.

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There was another matter requiring further investigation. At Culver we had been surprised to find that, in certain directions, errors in bearing up to 3 degrees could occur, the magnitude of the error depending on the range of the target. This turned out to be the result of a reflected wave from sloping ground in front of the aerials interfering with the direct wave from the target. Obviously, the effect had serious operational implications and Professor N. F. Mott was asked to look into it from the theoretical point of view. A rather similar phenomenon had been observed with early radio direction finders and, if I had paid more attention to what T. L. Eckersley and his colleagues had said on the subject, I might not have been so surprised by the results we obtained at Culver. The proposal to carry out further siting trials was accepted and steps were taken for suitable mobile equipment to be constructed at Christchurch. The plan was that, when this was ready, CAEE would provide personnel and logistic support. In the meantime, the experts at Christchurch thought that some improvement might be obtained in the matter of permanent echoes by reducing the distance between the dipoles and the wire netting reflectors. Accordingly, during the month of August, I paid further visits to the Isle of Wight and carried out a new series of trials. No very spectacular results were achieved but a modified aerial system was eventually arrived at that was thought to be an improvement on the original one. I enjoyed those trips to the Isle of Wight and oddly enough look back on the period as a peaceful one, although in fact the war was raging about us. The ferry that connected Lymington on the mainland with Yarmouth on the Isle of Wight was being fitted with protection against magnetic mines in the form of encircling cables carrying current. One day from Culver we saw an enemy aircraft making an unsuccessful attempt to bomb a small vessel. On 12 August, whether from the Isle of Wight or from the mainland I cannot remember, I saw enemy aircraft dive bombing a target, which, although I did not know it, was the Ventnor Chain station. A number of other radar stations were bombed on the same day, but surprisingly this was not the beginning of a general attack on radar stations. Ventnor was the only station to be out of action for a significant period. The mobile site testing equipment was put together in a remarkably short space of time, and on 5 September it was ready to leave for Llandudno, where the trials were to be conducted. Llandudno afforded a number of sites on and around the Great Ormes Head that were very suitable for trials of this nature. A decision had been taken some time before that CAEE would move there from the Isle of Wight.

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The transmitter and receiver were contained in a pair of cabins each mounted on a turntable attached to a chassis fitted with wheels so that it could be towed behind a truck. When the equipment was to be deployed, the weight was taken off the wheels of each cabin by means of screw jacks provided for the purpose. A lattice structure was then built on the top of the cabins using ordinary builders’ scaffolding, cut into lengths. When this had been done the aerials were hauled up one side so that the tops were thirty feet from the ground. Twenty to thirty men were needed to man the equipment, this number pro­ viding for the mounting of the necessary guards when the equipment was left in situ. The troops appeared to enjoy the job of erecting the scaffolding and the whole deployment took less than half an hour. I believe that it was my idea to use tubular steel scaffolding in this way and, in spite of some initial misgivings about stability, the scheme was a success. The General Staff were very anxious to have the results of the siting trials, and they were rushed through in the space of two weeks. The reason for this urgency was that the occupadon by the enemy of northern France had made the South Coast of England very exposed, and a project to establish a chain of radar stations intended for coast watching, that is, detecting the approach of hostile vessels, was being pushed forward with very high priority. The stations were to be similar to CHL stations, but they were to be operated by the Army and the new chain was to be endrely distinct from the CHL chain proper whose role was the detection of low flying aircraft. Somewhat con­ fusingly, the new chain became known as the CD/CHL chain. Our contribution to this effort was to draw up, on the basis of the informadon obtained from the trials at Llandudno, a set of rules for the siting of CD/CHL stations. Meanwhile in Christchurch steps were being taken to install the first production CD fire control set—afterwards known as CA No. 1 Mk 1—in a pair of huts at Steamer Point ready for a brief trial. It was hoped that this would culminate in a demonstration that the equipment was in a proper state to be sent to CAEE at Llandudno for more extensive trials. The demonstration took place early in De­ cember. In order to check the results given by the CD set I arranged for the position of the target to be determined optically using two theodolites, one adjacent to the CD set and one a few miles along the coast. The results were plotted on a large board as they were received and were thus available for inspection immediately the trial was com­ pleted. For artillery purposes one is more concerned with consistency than absolute accuracy. When systematic errors had been allowed for,

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the average bearing error was about 10 minutes of arc and the range error something less than 50 yards. Careful organization and good drill are necessary for a successful demonstration of this kind to be mounted, particularly if it is to be in the presence of senior officers. I had an increase in confidence when all went off smoothly. The equipment was packed up into trucks and sent off to Llandudno where huts and gantries were ready for it. I took up residence at the Castle Hotel in Deganwy early in January and was there almost con­ tinuously until the latter part of April. We soon confirmed the existence of the site errors that Professor Mott had predicted on the basis of a survey that had been done. We spent much time in calibrating the installation for these errors. AA Command obligingly lent us a 3.7 inch mobile gun and we did some trials to see what sort of echoes we could obtain from shell splashes. Work on 50 centimetres had not entirely ceased at ADEE after the initial discouragement and we were sent some 50 centimetre equipment for comparative trial. Work on 10 centimetres was, however, now going so well that there was little possibility of 50 centimetres being adopted. I was instructed to refer a technical point about the aerials to Shire; he replied, but added that it was all a waste of time. Forshaw wrote to me about the middle of April and asked me to finish up my work at Llandudno within the next two weeks, with a view to returning to Christchurch to take charge of trials of GL Mk III, a 10 centimetre anti-aircraft gun-laying equipment. I did return to Christchurch, but events took a different turn as far as my future activities were concerned. During the period that I had been struggling with the problems of CD siting and performance, Cockcroft had been engaged on matters of much more far-reaching importance. In August I had heard him say that he was off to the United States “carrying Tizard’s bag”. This was in fact the famous mission, led by Sir Henry Tizard, which initiated the close collaboration that afterwards took place between the United States and the United Kingdom in the air defence field. One of the things that the bag contained was a cavity magnetron. On his return to the United Kingdom at the end of the year, Cockcroft resumed his interest in Army radar. He was asked to examine the work of ADEE and to make recommendations for its future organi­ zation. From his report it was clear that the establishment needed someone of stature and authority at its head, and Cockcroft himself was invited to accept this responsibility. Accordingly, in April 1941 he became Chief Superintendent, the name of the establishment being changed to the Air Defence Research and Development Establishment

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(ADRDE). Up to that time Col. C. H. Sylvester Evans, O.B.E., T.D., had been Commandant and the Superintendent reported to him or, at any rate, through him. This was a reversal of roles since in peace time Evans had been a member of the scientific staff of the Estab­ lishment and as such had come under the Superintendent. However, he was also a Territorial Colonel and when war was imminent had put on his uniform. In all my dealings with him, I found him a man of charm and modesty. On the day of the take-over he published two station orders on the same sheet of paper. One announced the change of name of the Establishment and stated that Cockcroft was to be Chief Superintendent. This he signed as Commandant, ADEE. The other was a routine order of some minor kind and was signed Com­ mandant for Chief Superintendent. He thus made it clear where we all stood and in particular where he stood himself.

7 Operational research

One of Cockcroft’s first objectives on becoming head of ADRDE was to bring the establishment more closely into touch with operations in Anti-Aircraft Command. He had himself been kept informed of what was going on by Blackett who was sciendfic advisor to the Commanderin-Chief, General Sir Frederick Pile. I had myself met Pile at Christ­ church shortly before Young left to take over his post at the Ministry of Supply. He was small in stature for a soldier, quick and bird-like in demeanour, and full of enthusiasm for scientific aids. He saw the importance not only of having whatever new devices could be provided, but also of making the ones that he had work as well as possible. The only radar equipment in AA Command in September 1940 was GL Mark I which could give range and approximate bearing, but had no way of measuring elevation. It was useful as an aid in picking up targets for visual engagement in daylight, but was of no use for unseen fire at night, which was when practically all the enemy raids took place. This deficiency was due to be rectified in GL Mark II, but delivery of this equipment lay well in the future. As an interim measure, an elevation finding attachment based on the same principle as that used in GL Mark II was devised by L. H. Bedford of the Cossor Company, and it was characteristic of Pile to insist that the major task of converting all GL Mark I sets in the Command should be undertaken. Unfor­ tunately, while the system worked after a fashion when Mr Bedford himself or one of his minions was present, it was not robust enough nor stable enough to stand up to service conditions. In any case radar maintenance personnel were very thin on the ground. The answer was to recruit a large number of biologists from the Universities —the physicists and engineers were already on war service —together with a number of school teachers, rush them through a course of training

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and post them to batteries as Radio Officers. A school was set up at Petersham in the Old Vicarage with Ratcliffe, seconded from TRE, as Superintendent and Shire as his deputy. Training started from scratch— Shire used to lecture on “Brush up your electricity” —but the quality of the intake was such that after a few weeks the men were capable of nursing a GL set. Although they were civilians and their duties cut across those of the Ordnance Corps —which before the formation of the Royal Electrical and Mechanical Engineers (R.E.M.E.) was respon­ sible for the maintenance of radar equipment—they were on the whole well received by the batteries and, if in a particular instance they were not, Pile knew well enough how to deal with the problem. From the beginning Ratcliffe organized a weekly meeting on Saturday mornings at which all concerned, including Radio Officers in post and in training, could compare notes. This was more in accordance with academic practice than with military procedure, and an officer from the Ministry of Supply, who was present at the first meeting on 16 November 1940, included in his report a severe comment on the irregularity of what went on. However, such things did not trouble General Pile in the least. He showed his warm support by turning up in person at the second meeting, accompanied by Blackett and also by Sir Frank Smith from the Ministry of Supply. The dissenting officer, finding himself in the presence of his betters, wisely decided to make no further comment. There were then Radio Officers on eight sites and it was clear from their reports that they had been able to effect an improvement. It is only fair to say, however, that the early Radio Officers were exceptional in that they were men of some experience who had been seconded by electronic firms. By early December, eighteen Radio Officers had qualified and some were soon to be posted to gun sites in the provinces as well as to those near London. The period was, of course, one of persistent air attack. Ratcliffe soon found that he needed not only to train Radio Officers, but to do experimental work in order to check up on their findings and be able to feed them with further information. It was discovered that the coaxial feeders had to be “stroked” or flexed at intervals in order to preserve their efficiency. It was also found that a better performance could be achieved if the feeders were cut to a resonant length instead of being terminated with resistors and a great movement for the installation of “critical” feeders was set on foot. On many gun sites the ground was not flat enough for the Bedford attachment to work accurately; the answer to this was to install a wire-netting mat

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160 feet in diameter around the receiver cabin. By the early part of December 12 held detachments were engaged in this work. In about April 1941 Blackett left AA Command to go to Coastal Command and the question arose as to the future of the group of scientists that Blackett had assembled around him. I believe that Pile would have liked Cockcroft to take over Blackett’s duties as Scientific Adviser, but Cockcroft obviously could not do this as well as acting as Chief Superintendent of ADRDE. By this time the school at Petersham was running smoothly and Ratcliffe had energy to spare. It was there­ fore agreed that a group should be formed at Petersham under Ratcliffe which would include Blackett’s former group and also the people who had been doing experimental work at the school. There were two main sections in the group as it was set up. One, composed entirely of Blackett’s former people, was under L. E. Bayliss and was concerned with questions of hre control, particularly with the behaviour of predictors when fed with the very unsmooth data that came from GL sets. I was brought in to be in charge of the radar section. Cockcroft ruled that I should continue to be responsible, as far as ADRDE was concerned, for the work still going on in Llandudno. However, it was clear that I could not also conduct the trials of GL Mark III at Christchurch. Black was disappointed about this and so was I, but I felt excited at the prospect of coming nearer to the war as it was being fought. During the severe air attacks of the autumn and winter of 1940 I had been safely in Llandudno, where we had never had a bomb and hardly ever an air-raid warning. I lost no time in reporting to Ratcliffe at Petersham. I found him in a characteristic state of effective activity, dealing with many things at once. He did, however, find time to give me a briefing and by following him around I was able to get a good idea of what was going on. Later, when I had settled in, Ratcliffe took me to the headquarters of AA Command at Stanmore and introduced me to Lt. Col. Fremande, the Staff Officer whose province included radar. Fremantle had a precise appreciation of what scientific officers could do for anti-aircraft defence and we were fortunate in that there was an officer of his calibre so placed in AA Command. He took us into the operations room and he pointed out, on a map showing the plots of the night before, an aircraft track that came from the direction of Germany, across to Scotland, and stopped abruptly on the west coast. Beyond pointing it out he made no further comment. It was, in fact, the track of the dramatic flight that Rudolph Hess made on the night of Saturday 10 May. I came away from Stanmore armed with a pass valid for all

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sites and installations of AA Command and felt ready for any demands that might be made on me. The inadequacy of the early GL sets for unseen hre and the tactics of the enemy in sending aircraft over in waves made it difficult for the batteries to engage individual aircraft and in some areas, London in particular, Divisional Commanders had resorted to barrage hre. The Divisional Commander himself would order a barrage to be put up at such and such a place in the sky. If he relied on plots of enemy aircraft passed to him by the manual systems then operating there was a good chance that he would order the barrage long after the aircraft had passed. The latest enthusiasm in AA Command was, therefore, to have a remote radar display provided in the divisional operations room. Whatever doubts one might have had about the effectiveness of barrage fire, even under the most favourable circum­ stances, one was forced to admit that it was better than nothing. Soon there was a great scamper of activity to get the new system going in the London area. The idea was to use a mobile CHL set of the type that had been developed by the RAF for ground control of interception (GCI). This resembled the site testing mobile set that I had developed except that the aerials were mounted near to the ground. The display was of the plan position indicator (PPI) type developed a little earlier at TRE. This used a cathode ray with a long after-glow screen on which the tracks of aircraft were painted by a rotating intensity-modulated time base, so that the observer was presented with a plan view of the situation. Normally the display was near to the radar receiver and it was a new idea to pipe the information along wires to an operation room several miles away. One of my first jobs at Petersham was to organize trials in order to locate a good site for the equipment. For this purpose I borrowed the mobile equipment that I had used for the siting trials in North Wales. I tried Richmond Park and also Flyde Park where there was already a gun site. I recommended the latter. The remote display was to be located in the operations room of the 1st AA Division, which was underground in a disused tube station in Brompton Road. Someone suggested that it would be worthwhile consulting H. L. Kirke, the chief engineer of the BBC, with regard to the transmission problems involved. 405 line television was operating in London as early as 1936 and was only closed down on the outbreak of war. The BBC had, therefore, much experience of the transmission of video signals. I went to see Kirke in his office and very much enjoyed meeting him. On one matter our discussions showed an interesting difference of approach. I was

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all for using cathode followers, whereas he thought in terms of carefully designed pulse transformers. At one point he gave me a shrewd look, and asked me whether I had ever worked at EMI (Electrical and Musical Industries, Ltd), since my technique would appear to suggest that. I now realize that the approach to circuit design that I had met at Bawdsey had largely originated with A. D. Blumlein who had played a major part in the development of television at EMI. It is a source of regret to me that I never met Blumlein. He was killed while doing experimental flying with the RAF on 7 June 1942. In June 197 7 I was present at the unveiling by Alan Hodgkin, Past President of the Royal Society, of a memorial plaque set up by the Greater London Council on the house in Ealing where he had lived. Many statesmen and other public figures have been honoured in this way, but Blumlein was the first engineer. There was little difficulty about the transmission of the video signal, but the rotation of the time base presented distinct problems. In early PPIs the deflecting coils producing the time base were rotated about the neck of the tube by a Selsyn motor driven from a corresponding motor attached to the turntable. This worked very well over a short distance when the voltage drop in the cables was negligible. We thought of many ways of transmitting the rotation along telephone wires and no doubt, if we had had more time, could have arrived at an elegant solution. In fact, however, it was decided to take the easy way out and install a heavy cable, General Pile being only too pleased to supply a detachment of troops to dig a trench across Hyde Park. It was fortunate indeed that I had been able to recommend Hyde Park instead of the much more distant Richmond Park as a site for the station. An enormous effort, quite out of proportion to its value, was devoted to this project. By 21 June Ratcliffe could report to Cockcroft that the equipment was in partial working order with four Radio Officers at­ tached, including D. F. Pike in charge and G. C. Varley in technical charge of the apparatus. It was not until nearly the end of July that the equipment was tested under operational conditions and then only during a night raid in which less than 50 aircraft took part. However, the results were regarded as encouraging and at a meeting held on 1 August at AA Command, at which everyone concerned from General Pile downwards was present, plans were laid for extending the system to other parts of the Command. Pike was sent off to do a reconnaissance in the Mersey and Clyde areas. An important limitation of the system was that the PPI had to be viewed in semi-darkness and could not, therefore, be put where the Divisional Commander himself could see it. At Brompton Road it was

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installed in a small darkened cubicle and information was passed out by an operator. The problem of providing a PPI display that could be used in an ordinary operations room was never solved during the war. At the beginning of 1943 we had demonstrations of a colour trace tube, known as the Skiatron, in which the electron beam produced a dark mark on a white screen that could be viewed in ordinary lighting. The mark was supposed to persist for some minutes and then gradually fade away. The difficulty was that this fading did not take place sufficiently rapidly or completely and the screen soon became foil of old tracks. It was a great disappointment that what appeared at first sight to be a very promising device should have proved incapable of development. At the beginning of August 1941 Ratcliffe was recalled to TRE where he started a radio school for the RAF and initiated other activities that I shall have occasion to refer to at length later. It was decided to split off the operational research group at Petersham from the AA Command school and to reorganize it as an integral part of ADRDE. The new head of the school was Major P. Johnson who had been attached for some time as an Instructor-in-Gunnery. In peace time, Johnson was a Fellow of Magdalen College, Oxford, and before joining the Territorial Army as a gunner had obtained his wings as a member of the Auxiliary Air Force. He was later to take operational research to the Middle East and during the invasion of Europe commanded an Operational Research Section attached to the 21st Army Group. The new Superintendent of the operational research group was Col. B. F. J. Schonland and this proved a brilliant choice. Schonland was a South African by nationality. He had been trained in the Cavendish Laboratory and had made his life’s work the study of thunderstorms and lightning, a subject for which the South African climate provides exceptional opportunities. Moreover, since thunderstorms are of great economic importance in South Africa, Schonland had been able to obtain generous support for his work. He had planned the establishment of the Bernard Price Institute for geophysical research and had become its Director as well as being a Professor in the University of Witwatersrand. In 1938 he was elected a Fellow of the Royal Society. There was, therefore, no doubt about Schonland’s scientific standing. How­ ever, the important point was that he was also a convincing soldier. Indeed it is as a soldier that I primarily think of him, since I rarely saw him out of uniform. He once remarked to me that he had spent a large proportion—nearly a third—of his adult career in the army. In 1915 while a student in Cambridge he had responded to Kitchener’s call and had served in France with distinction as a signals officer. Very

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soon after the outbreak of the second World War he was in uniform again. Schonland was a fervent admirer of Cockcroft, whose actions he would never criticize. Schonland had been sent to England by the South Africa Government to investigate the state of radar and he had visited Llandudno at the time we were studying site errors with the 150 centimetre CD equip­ ment. He told me later that he regarded our patient and meticulous work in plotting bearing errors, amounting in places only to a few minutes of arc, as being one of the curiosities of radar. Perhaps we did spend more time on it than was absolutely necessary. It would be difficult to think of two people less alike than Ratcliffe and Schonland; nevertheless, the changeover went with remarkable smoothness and as time went on the organization that Ratcliffe had originally created proved capable of being developed to meet new needs. Bayliss remained responsible for investigating the fundamental problems of unseen AA hre and for endeavouring to determine the accuracy of hre actually being attained. I was more concerned with solving technical radar problems and with giving AA Command the support it needed when introducing new equipment. I was able to build up good trials facilities in Richmond Park and I established a small but adequate workshop where experimental equipment, both mechanical and electronic, could be made. There was a third section in the Group, less high powered than the other two, which was re­ sponsible for collecting information about the number of rounds bred and the number of aircraft shot down, and for preparing statistical summaries. Attempts to develop this section by bringing in statistical expertise were not successful and it was, I believe, later on taken over by Bayliss. As gradually we became more formally organized Bayliss’ section became known as ORS 1 and mine as ORS 2, the whole group being known as ADRDE (ORG). When GL Mark II came along we found ourselves very busy doing trials and helping to introduce the new equipment into the service. The ground had, however, been well prepared. There was much ex­ perience in the Command in the use of radar equipment on gun sites and there were a large number of radio officers who had had directly relevant experience with the earlier equipment. The same was not true of SCL or “Elsie” as it was universally called. This was a radar set specially designed for putting a searchlight on a target. It had been conceived as early as April 1940 by three junior scientific officers at Christchurch, W. S. Eastwood, D. R. Chick, and A. J. Oxford. Their aim was to design something simple enough to be manufactured and brought into use on a large scale with the minimum of delay. They

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based their design on airborne 150 centimetre radar units already in production for the RAF and mounted them, together with the necessary aerials, on the searchlight itself. Elsie broke new ground and there is no doubt that it was very successful. It was, however, something of a tour deforce to accommodate the transmitter, receiver, and display units, together with the aerials, on a searchlight that had not been designed to receive them and to provide an adequate degree of protection against the weather. Op­ erational conditions are very different from the conditions that exist when trials are being conducted, and they are apt to show up un­ suspected problems. While these problems may be quite minor tech­ nically, they can prevent the equipment from fulfilling its operational role. Naturally, there is much urgency about solving them. Elsie was no exception in this respect and soon AA Command were in real trouble. One of our officers was of an inventive turn of mind and in the scurry we became involved in technical controversy with the design group at Christchurch about certain modifications that should be made. We should have avoided this at all costs. I had seen the rocks ahead clearly enough, but Schonland, who had not done so, had encouraged the inventive officer. It was inevitable that we should get the worst of the argument and, for a time, our effectiveness was reduced. The major innovation of mounting radar equipment on a searchlight was successfully accomplished. There remained a further problem which was in some ways more difficult to solve since all the experience accumulated with searchlights in the peace time Army indicated that it should not exist. It concerned the changeover to visual following once the target had been picked up with the aid of Elsie. According to accepted doctrine this should have been straightforward for a welltrained detachment. It was certainly not straightforward under wartime conditions in AA Command. It was very hard for an operator on the searchlight itself to keep a high flying target illuminated since he was too near to the beam. It seemed to AA Command and ourselves that the obvious answer was remote operation from a control pillar sited to one side. This was eventually achieved, but only after much arguing with the many establishments and ministerial branches involved. My right-hand man on the GL side was J. B. Hby, who, in fact, later took over the AA Command liaison altogether. We had been much concerned about the effect of enemy jamming of radar systems, and gun sites had been instructed to report on any unusual signals that they received. We were particularly concerned about the possibility of the enemy using airborne jammers. Hey had a special responsibility in this area and one day he showed me a series of reports that had

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come in from certain widely scattered gun sites. These sites all reported an increase in receiver noise when the aerials were pointed in a certain direction. This direction slowly changed during the course of the day. Hey had obtained some figures showing how the bearing of the sun changed with time and it appeared that the noise followed the sun. At that time I was quite unprepared for the idea that the sun could radiate on a wave-length of three or four metres and I regret to record that I did not show the willingness that a good scientist should to make an impartial examination of evidence. After the war, Hey re­ mained in Government service and was able to follow up his wartime observations. By then the new science of radio astronomy was getting under way, and Hey became the leader of a very successful group. As far as AA Command was concerned my section was there pri­ marily to provide technical support in relation to radar equipment, operational research proper in anti-aircraft gunnery being done by Bayliss. There was, however, another sphere of activity in which we had the whole field to ourselves. This was coast watching and coast artillery. The credit for what we achieved in this sphere goes to three very able officers. The first was George Varley, a Cambridge zoologist of about my own age, who had been trained as a radio officer and whom I have already mentioned in connection with the Hyde Park exercise. The second was David Lack, a somewhat older man who had already achieved a reputation as an ornithologist that he was later to consolidate. The third was Philip Varley, brother of George and a captain in an infantry regiment. He had had a scientific training and it had proved possible to arrange his posting for radar work. Together these three officers did much to help the army improve the efficiency of the coast defences. They became famous for their energy and forcefulness, which they managed to combine with a singular ability for getting on well with people. The CD/CHL chain had been hastily sited. It urgently required review and extension to the east and west. George Varley and Lack played a part in this work. However, even when a first class site could be found, the range of the 150 centimetre equipment was not good and on most sites it was wholly inadequate. Lack, in an ORG report, drew the attention of the General Staff to the fact that cover was very bad in two places where disagreeable incidents had occurred in the past, namely in 55 B.C. and in 1066 A.D. The solution, of course, was to install 10 centimetre equipment. Fortunately, as a result of a brilliant piece of development by the Admiralty Signal Establishment, such equipment became available at the right time. It was known as the NT2 71 and was based on the fundamental work done at Birmingham

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and at TRE in 1940. The NT271 and later developments of it became the standard equipment for both land-based and ship-home use. Cock­ croft managed to get a very early NT271 and this was installed by A. E. Kempton in a rotating cabin fitted with a pair of six-foot parab­ oloids. It was then sent to Dover where it became operational early in August with George Varley to look after it. Soon he was reporting excellent results. Even E-boats could not go between Calais and Boul­ ogne undetected and large ships could be watched at anchor in the outer harbour of Boulogne. The operational situation was transformed. Before August 1941, there was only a small chance that enemy ships passing through the Straits would be detected and attacked, even in daylight. By October, the passage had become much more dangerous and the enemy would only attempt it by night, when conditions were less favourable to the attackers. These results were so encouraging that steps were taken to site further stations around the coast to take over the coast-watching role from the original CD/CHL chain. At low-lying sites it was decided to mount the paraboloids at the top of 200 foot high towers and the first of these stations was working by August 1942. As a result of these developments we had a coast-watching chain that enabled real pro­ tection to be given to allied convoys passing along the south coast. Associated with the new coast-watching chain was a high-powered 10 centimetre station at Ventnor on the Isle of Wight. This had been erected within the compound of the RAF Chain station with the support of Air Marshall Joubert who was then Commander-in-Chief of Coastal Command. George Varley was attached to this station, and I remember going down to see him towards the end of April when it had been working for some weeks. Cockcroft took a special interest in the project. The hope was that it would be possible to see shipping near the Cherbourg peninsula. Even though the station at Ventnor was 700 feet above sea level this was well beyond the optical range, but it was known that under suitable atmospheric conditions propagation to be­ yond the optical range was possible. The phenomenon was referred to as anomalous propagation and occurred when the proportion of water vapour in the atmosphere increased with height. This could, in particular, happen during the summer months at night when cool dry air from the land moved out over the sea and pushed upwards the warm moist air originally there. The expectation that anomalous prop­ agation might be observed to a very marked degree from Ventnor was borne out in practice. During June 1942 it occurred for more than half the time, but this was unusual. Cockcroft was at Ventnor on 19

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August 1942 just after the Dieppe raid and saw shipping all the way to Dieppe over 100 miles away. It was clear that since anomalous propagation was of operational importance there would be some advantage in being able to forecast its occurrence, and George Varley tried his hand at this in an amateur way. Schonland and I went to see Dr Nelson K. Johnson, who was then Director of the Meteorological Office, to enquire whether an official forecasting service could be provided. He received us kindly enough, but after we had come away Schonland remarked that he had felt that we were adding just one more small problem to the many large problems that Johnson was facing. However I believe that eventually something was arranged. The anomalous propagation of ultra-short waves was of some scientific interest and Appleton had set up a panel to study the subject. When he heard of my interest he invited me to join. The success of the 10 centimetre coast-watching equipment drew attention to the desirability of converting the CA No. 1 Mark I fire control equipment to 10 centimetres. I was very keen on this as I had no confidence at all in the utility of the 150 centimetre version and I was in a good position to form a judgement. Apart from giving greater range and freedom from site errors, conversion to 10 centi­ metres would, on account of the shorter pulse length and better bearing discrimination, give a real chance of observing the fall of shot. Fall of shot observation is the key to all accurate gunnery. At my instigation Schonland spoke to Cockcroft on the subject in July 1941, but it was some time before a positive decision could be obtained. Early in De­ cember George Varley reported from Dover that the NT271 equipment was being used for firing by six-inch guns at small enemy vessels found to be approaching the English coast. The equipment was not suitable for the purpose but there was nothing better. On a number of occasions large vessels within range of the 9.2 inch battery had been seen to pass the Channel, near to the French coast, but could not be engaged. A 10 centimetre fire control set with continuous transmission of range and bearing would be of immediate operational use. Cockcroft acted on this and was able to get authority to install such a set at Dover for experimental purposes. This set, which was known as B(p)X, was installed in March 1942. Meanwhile an incident had occurred that had caused something of a flurry. On 12 February 1942 the enemy attempted —successfully — to pass the pocket battleships Scharnhorst and Gneisenau through the Channel in an eastward direction. He was evidently concerned about our radar stations and effectively jammed those working on 150 cen-

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timetres; significantly there was no jamming on 10 centimetres. Tracks were picked up by the NT2 71 station at Fairlight just east of Hastings at 1050 hours; these were passed to the Naval Operations room, but were not passed promptly, as they should have been, to the Coast Artillery Operations room. However, the 9.2 inch battery at South Harland was able to open fire at 1219. Two reports of fall of shot were received from radar stations and one of these enabled the gun range to be increased, with the result that the next salvo was reported a “hit or near miss”. Sayer states, in his History of Army Radar, that it was, in fact, confirmed much later that three out of the thirty-three rounds fired made direct hits on the Gneisnau. The action ceased at 1236 hours when the targets passed out of range. This action is of some interest as being the last that is ever likely to take place between fixed coast guns and capital ships. From the British point of view it was most unfortunate that it was ruined by the initial failure to pass information promptly.'"' B(p)X was first used in action on the night of 2/3 July, 1942. It was now possible to bring effective fire to bear on large enemy ships that attempted to pass through the Channel. Perhaps the most gratifying feature was the surprising degree of success that was obtained in the plotting of shell splashes. For example, in an action that took place on the night of 10/11 November, all salvos fired from the 9.2 inch guns were observed and 13 out of 15 fired from the 15 inch guns were observed. It was, however, fully appreciated at ADRDE that the use of 3 centimetre waves would enable even better results to be obtained; as early as the summer of 1941 discussions had taken place on the design of a 3 centimetre shell splash indicator. The ultimate outcome was a highly advanced instrument designed and built by A. E. Kempton with the assistance of F. J. M. Farley and of an American officer Lieutenant Vollum. This had a twelve foot strip mirror designed to produce a very sharp beam of less that 1 degree width in the horizontal direction. The pulse length was a little more than 0.1 micro­ seconds, corresponding to a range discrimination between targets of about 25 yards. By means of a mechanical motion of the wave-guide feeding the mirror, the beam was made to oscillate continuously through an angle of 3 degrees and the received signals were exhibited "An interesting account of the operation as seen from the German point of view was published in 1955 by Captain H. J. Reinike of the German Navy who was aboard the S c h a r n h o r s t when she made her dash through the channel. It will be found in volume 81 of the Proceedings of the US Naval Institute.

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on a display which showed in plan position form an area of two thousand yards by 3 degrees. This device, which had an official name but was always known as “Charlie”, went to CAEE at Llandudno for trials in March 1943. We would have preferred that it should have gone straight to Dover. However, it did arrive at Dover in July and was an immediate success. From then on the coast gunners were better equipped for unseen fire than they had been for visual shooting in the pre-radar days. A number of successful engagements took place, although by that stage in the war there was a shortage of targets. The coast batteries at Dover were in action for the last time on 2/ 3 March 1945 and there then closed a chapter—now seen to have been the final chapter—in the long history of coast artillery. A number of copies of Charlie were made and I believe that two of these were sited at Ventnor and used during the invasion of France to help plot shipping in the channel, their high resolution proving of the greatest value in determining accurately the number of ships in the returning convoys. Shortly after the Scharnhorst/Gneisnau episode the celebrated raid on the German radar station at Bruneval, on the French coast, took place. Schonland had had some part in training the personnel for this raid. I knew that he had been engaged in some mysterious activity with troops on Salisbury Plain, from which he had come back complaining of the cold, but I did not know what it was. After the raid, when the announcement had been made in the press, he came bursting into my office in a mood of jubilation. He told me that parts of the equip­ ment had been brought back to this country. Why this fact was omitted in the press reports I could never understand, since it must have been clear enough to the Germans what had happened. I saw the pieces in London a few days later. They came from an equipment working on about 50 centimetres with a dipole mounted at the focus of a parabolic reflector. I had realized quite early in the exercise that measurement of echo amplitude might be of use in estimating the size of the ships being tracked. Accordingly, I had provided, for the use of the ORG officers on the coastal sites, signal generators which they could use to calibrate the gain control of the receiver. They soon worked out techniques for classifying vessels roughly according to size. The signal generators were not very reliable and rather awkward to use and Varley and Lack found that they could get sufficiently good results by calibrating the gain control on a fixed echo. I was not very happy about this procedure, but it appeared to work well enough in their hands. The methods they developed and introduced along the coast-watching chain were

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of great operational value and a good example of what can be achieved by trained scientists working on operational sites. Measurement of echo amplitude provided a solution to a problem that had been the source of no small worry from early days, namely, how to distinguish echoes from seagulls from very similar echoes coming from small craft, such as enemy E-boats. When first observed the former were a great mystery since they seemed to come from no material object, and they were referred to as “angels”. I remember meeting the problem myself when operating an experimental station at Steamer Point for the benefit of the Army during the invasion scare of 1940. We very nearly gave the alarm that would have set the whole defence machine in action. There was difficulty in believing that a bird could give an echo of the right amplitude, but this was later put beyond all doubt by Lt. Ramsay at CAEE, Llandudno. Ramsay sus­ pended a dead seagull from a balloon and observed the echo directly. He had earlier shot the bird in the Conway Estuary. This was, I believe, the only shot fired in anger by any of the officers or other ranks on the strength of CAEE in the entire history of that establishment and one can only regret that it was fired at a sitting bird. I always took advantage of any opportunity that offered during a trial of obtaining accurate measurements of echo strength as a function of range. Later, at Llandudno, with Ramsay’s help, I was able to get some absolute measurements of the strength of the echo received from a ship by first calibrating the equipment using the echo received from a metallized sphere suspended from a balloon. The equipment we used for this purpose was a 10 centimetre GL set whose aerials could be elevated so that the beam was clear of the ground. I worked out a theory by which the results obtained could be satisfactorily explained. At the end of the war, when steps were being taken to publish some of the work that had been done, I was invited to write a paper on the performance of radar on ship targets. This I did and published it jointly with Ramsay in the Proceedings of the Cambridge Philosophical Society in 1947. During the period that I have been writing about, the character of the Operations Research Group had been steadily changing. In the beginning it was concerned very much with technical radar problems. Now the interest was broadening. Shortly after Schonland came, a Signals Section was formed and steps were taken to comb the Army for scientifically qualified men who could be trained to do operational research in the field armies, particularly in connection with tank war­ fare. Among these was Michael Swann, who later occupied a number of important posts, including that of Chairman of the B.B.C. He was,

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I think, a lance corporal when he was first posted to us. In July 1942, the Deputy Chief of the Imperial General Staff wrote a paper proposing that the Operational Research Group should come under the control of the War Office, while remaining responsible to the Ministry of Supply for administration and technical efficiency, This paper showed a very clear appreciation of the functions and aims of operational research in wartime. The proposal was accepted and ADRDE (ORG) became an independent establishment under the name Army Op­ erations Research Group (AORG) on 1 February 1943. The change was welcomed by those in charge of administration at ADRDE since we were presenting them with all sorts of problems and I think they felt that we were rapidly getting out of hand. ADRDE itself had also undergone changes. In May 1942 the au­ thorities woke up to the fact that it was unwise to have both ADRDE and TRE situated on the south coast where they were obvious targets for enemy raids; after all, we had just shown what could be done by raiding the Bruneval station. Orders were therefore given that both establishments should be moved as quickly as possible. There was a story that Churchill had laid it down that they were to be moved by the next full moon, but A. P. Rowe says in his book that the story is probably apocryphal. It is true, however, that the move took place in a great hurry. Both establishments went to Malvern in Worcestershire. ADRDE took over a group of one-story buildings that had been erected before the war to provide for some such need. These proved to be very suitable for an experimental establishment. TRE occupied the buildings of Malvern College, which they augmented by the erection of various huts. Since it was thought that a coastal site was necessary for the development of CD equipment, a small sub-station with work­ shop facilities was built on the top of the Great Ormes Head at Llan­ dudno, not far from the CAEE experimental site. However, as time went on, the merit of locating the work at a coastal site became outweighed by the practical disadvantages of its being done in isolation from the rest of the Establishment, and accordingly the decision was taken to transfer it to Malvern and to regard the Llandudno outstation as being simply a trials establishment. Cockcroft asked me to go there to be in charge. Thus it came about that, on 5 July 1943, I packed my bags and set out to take up residence once more in the Castle Hotel, Deganwy, although I was not, as it turned out, to stay there very long. The point at which I left AORG marked for me the moment at which the heroic days of introducing radar into the Army were over. Over, also, were the doubts one had felt earlier as to whether radar really worked well

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enough to be useful for Army purposes. The striking success of the centimetric research had given rise to devices that one could really believe in. These were so far in an experimental form or had been produced only on a limited basis. The next step was for them to be manufactured and deployed on a scale commensurate with the op­ erations then in progress. The Castle Hotel remained the excellent hostelry that it had always been and one was as insulated there as one could hope to be from the shortages and privations of war. The enemy did not seem to have discovered that comer of North Wales. During the time that I was there the Fire Guard Order came out by which anyone in charge of a building was required to establish a regular rota of fire watchers and see that they were trained to deal with incendiary bombs. Anyone in the private sector failing to do what was required of him could incur heavy penalties, but a careful perusal of the order made it clear that the worst that could happen to a government official was that he might incur the displeasure of his superiors. Fire watching on the top of the Great Ormes Head seemed particularly pointless and I decided to risk that displeasure, which in fact never came. John Benson, now a Major and second in command of CAEE, kept his court in the Castle Hotel. Jimmy Vint and myself were also residents. We had many visitors from various branches of the Army and Ministry of Supply. A frequent visitor was Colonel Paterson from the branch at the Ministry of Supply known as A5, and when he came much secret business was done late at night in a private room at the Castle Hotel. My office on the top of the Great Ormes Head had a wonderful view across to Puffin Island. Unfortunately the building had been designed by an English architect who had made insufficient allowance for the penetrating quality of the Welsh rain. I wrote many minutes about the way it seemed to go straight through the walls. Nevertheless, on a fine day it could be a delightful spot and we often spoke of the possibility of turning the place into a hotel when the war was over. Alas, all that now remains is the concrete road leading up to the site and a few foundations. I have no clear recollection of the details of the work on which the Llandudno sub-station was principally engaged. Cockcroft, however, allowed me to put some of my effort into following up my interests in the way in which waves were reflected from ship targets, in particular by initiating a programme of work designed to study the fading of such reflected signals. This fading was a prominent feature of the signal returned from a ship. George and Philip Varley had found that

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they could get consistent results if they always measured the maximum amplitude attained during a period of twenty seconds. By recording photographically the individual pulses received from a target I had shown that the amplitude is distributed approximately according to Rayleigh’s theory for the composition of a large number of sine waves with random phases. In order to pursue the matter further I set R. I. B. Cooper, a young and able Junior Scientific Officer, to construct a device consisting of a series of mechanical counters driven by threshold circuits in such a way that each counter would record the length of time that the signal was above a certain fixed value. There were 12 counters altogether and the thresholds were set at intervals of 2.5 db. This apparatus was not finished when I left Llandudno, but Cooper continued with the work and eventually wrote an interesting report that was issued about a year later. I had been at Llandudno just three months when Cockcroft told me that he was under pressure to release people to TRE and would I like to go. It had apparently been decided that TRE needed to recruit some senior people from outside; I believe that what gave this demand some urgency was the fact that they had lost a number of people to work at the Atomic Energy Establishment at Chalk River in Canada. I agreed at once. I had wanted to go to TRE originally and I welcomed the change and the new experience that it would bring.

8 TRE

I arrived at Malvern in the late afternoon of 11 October 1943 and was allocated accommodation in a small private hotel situated on a steep road leading up from the centre of the little town to Malvern Hills. At dinner I found myself sharing a table with another man of about my own age. I am afraid that to begin with we glared at each other. As things went at that time the meal was by no means bad, but I was missing the superior qualities of the Castle Hotel and my friends there. When we finally broke the ice it appeared that he had been tom away from the Post Office Research Station at Dollis Hill and from his home, and was feeling rather as I did. That was how I first met Harold Stanesby. We became firm friends and remained so until his death. The TRE school laid on a short course for us and took us on a tour of the establishment; afterwards we were interviewed by the various divisional leaders. I was allocated to the Oboe Division. Oboe was a blind bombing system that depended on measurement of range from two land-based stations to the bombing aircraft. This was done by the usual radar method of measuring the transit time of pulses, but, since the bombing aircraft was normally much too far away for a normal echo to be received, it was necessary that it should carry a transponder which, on receipt of a pulse from a ground station, would immediately transmit a similar pulse strong enough to be re­ ceived at the same ground station. The pilot was guided so as to fly along an arc of a circle centred on one of the ground stations and having the proper radius to cause him to pass over the target. If he were on one side of the correct track he would hear in his headset a series of Morse N’s, while on the other side he would hear a series of A’s. To the pilot, therefore, it appeared exacdy as though he were flying along an ordinary navigational beam. He would receive signals

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telling him when he was approaching the target and when to release his bombs. Since a pair of ground stations could control only one bomber at a time, the method used was for Oboe-controlled aircraft to drop flares over the target and for the main bomber force to drop their bombs on to these flares. A special RAF group, known as the Pathfinder Group, provided the Oboe-controlled aircraft. These were all Mosquitoes capable of flying so high and fast as to be almost invulnerable to enemy attack. To me, one of the most surprising things about Oboe was that it used an absolute method of locating targets on the ground, the distances being computed from map-references. It depended on the fact that the relationship between the Ordnance Survey of Great Britain and the corresponding Survey of Germany was known with sufficiently high precision. The head of the Oboe Division, and indeed the inventor of Oboe, was Mr. A. H. Reeves. I much wish that, during the time that I was with the Oboe Division, I had become better acquainted with Reeves. Although I did not know it then, it was he who originally proposed using pulse code modulation for telephony. This proposal was far ahead of its time when he made it in 1937, and it is only with the development of semi-conductor technology that it has come into its own. Reeves was some 10 years older than myself, and taciturn, or at any rate unapproachable, in manner. He had spent his working life in the telephone industry and was on leave from Standard Tele­ phones and Cables Ltd. His background and that of his immediate cronies was wholly different from mine and indeed wholly different from that of almost everybody in the radar world of that time. I found it a salutary and slightly disturbing experience to have to explain myself to people who thought in terms of recurrent wave forms and phase differences rather than in terms of pulses and time intervals. This difference of technological background perhaps accounted for the fact that the Oboe Division kept itself somewhat apart from the rest of the establishment. As a Division it was organized in an unusual way in that it contained only one group. This was under the leadership of F. E. Jones, a man who possessed many qualities, the most obvious being his dynamism. The two Oboe ground stations were at Dover and Cromer. The Dover station was, I believe, an old CD/CHL; at any rate I remember feeling somewhat indignant during my AORG days when informed that one of those stations was being taken over by the RAF for some unspecified and secret purpose. The first thing I did for the Oboe Division was to play a small part in an accuracy trial that was being planned. It was proposed to fly an aircraft westward over the tip of

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Cornwall and, in order to locate its position with accuracy, a GL set had been borrowed from the Army. I was sent down to Penzance to check up on the siting of this equipment. I would have liked to stay there for a few days’ holiday, but in fact I came straight back. Oboe Mark 1 had first been used operationally in December 1942 for a raid on Essen. Since it operated on 150 centimetres it had not been expected that it would remain unjammed for very long. Ac­ cordingly Oboe Mark 2, which operated on 10 centimetres had been designed and the stations were in course of erection. In fact, however, Oboe Mark 1 was still going strong after nearly a year of use and continued to do so for some time; much destruction was wrought in the Ruhr with its aid. Jamming would have been very simple and one can only conclude that, during all those months, the enemy knew nothing about it, either from intelligence sources or by monitoring the signals. Oboe Mark 2 was designed to control a number of bomber aircraft simultaneously instead of only one. A separate pulse recurrence fre­ quency was allocated to each aircraft, and the receiver in it would respond only to pulses on that frequency. The first ground station was being built at Deal, the contractor being Standard Telephones and Cables, Ltd (STC). I was appointed the principal liaison officer for this project, and I spent a good deal of time at Deal with Mr. HeatonArmstrong, the STC engineer in charge. My service with the Oboe Division was interesting in giving me a window, even if a narrow one, on the bomber offensive, which of all warlike activities was the one that, by Cabinet ruling, had the highest priority. It was, however, not the kind of work for which my experience best fitted me, and even at that time in the war I had certain unresolved ethical problems in regard to the bombing of industrial and civilian targets. When, therefore, the opportunity arose for me to work once again for my old chief, Mr. Ratcliffe, I was glad to take it. When Ratcliffe returned to TRE in May 1942 it was to start a radar school to serve the needs of the RAF. He extended his activities into various forms of service liaison. The one with which I became involved was known as Post Design Services, or PDS, and it had as its object the bridging of the gap between the design and type-approval of equipment and its becoming a regular production item in routine use by the RAF. The school itself flourished under the immediate man­ agement of L. G. H. Huxley and by 1945 nearly 6,000 people had passed through it. The PDS Division was run by W. L. Francis and my particular concern was with airborne equipment for Fighter Command and

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Coastal Command. Equipment designed by TRE was frequently in­ troduced to the service in two stages. First there would be a crash program to equip a few selected squadrons with hand-made, or pardy hand-made, equipment. These crash programs were usually initiated by the Ministry of Aircraft Production under pressure from the Commander-in-Chief (egged on, more often then not, by TRE) in order to meet some immediate operational need or to keep one step ahead of the enemy. Later, equipment would come off the production line and more and more squadrons would receive it. At all stages the function of PDS was to supply officers who had an expert knowledge of the equipment and who could go on to squadrons to help sort out difficulties. The good ones were in much demand, and we were some­ times embarrassed by high-level requests for the services of a particular officer when he was in the middle of doing some other important job elsewhere. When new equipment was introduced it was always some time before the RAF stores organization was working smoothly and in practice, if not in theory, one of the functions of PDS was to provide a bootleg channel by which urgently needed components and other items could reach squadrons. This, of course, was a situation that I was well aware of from my army experience. The fact that a PDS officer did not go empty-handed was a major help to him in securing co-operation at the squadron level. Some components, such as resistors, had their values indicated by coloured bands or spots painted on them and I used to compare the handful of brightly coloured resistors that a PDS officer would take with him to the trinkets and other baubles which early explorers would use to help make friends with the natives. The beginning of 1944 was a particularly interesting time to join the PDS Division, since radar equipment designed and produced in America was coming into service in RAF aircraft. We endeavoured to provide for this a similar service to the one that we provided for British-designed equipment, in spite of the handicap of not being closely in touch with the designers, nor of having the same control over the production of documentation. Under arrangements made in Washington, the American manufacturers sent over a number of tech­ nical representatives who were attached to PDS and were of great assistance. The equipments themselves contained no major innovations as compared with their British counterparts, but they were beautifully designed and manufactured. It was evident on the most cursory ex­ amination that they had been produced under conditions very different from those in the factories of wartime England. At the beginning of 1944 the American night-fighter radar equipment SCR 720 (known in the British service as AI Mark X) was being fitted

THE

55

in Mosquito aircraft. This well-designed equipment included a rotating and tilting scanner mounted in the nose of the aircraft, and we soon found that this tended to stick when the aircraft was operating at high altitude. The trouble was due to the effect of cold on a set of micro­ switches mounted on the scanner and used to control the tilting. I forget whether we solved it by fitting improved switches or by intro­ ducing some heating into the nose of the aircraft. Whichever it was, it took some time, and in the interval the operational value of the equipment was seriously reduced. This unforeseen trouble was typical of those that PDS had to cope with. As time went on I found that more and more of my effort was being devoted to liaison with Coastal Command rather than Fighter Command. The principal role of Coastal Command, although its name did not suggest it, was to attack U-boats at sea. Early in the war U-boats began to operate in the Atlantic and to have very good success against merchant ships. The U-boats of that period were very little improved compared with those of the First World War. Their speed and endurance when submerged were both very low, since they had to rely for propulsion on the energy stored in their batteries. In fact a U-boat could only keep up its maximum submerged speed of 7.6 knots for one hour, and even if content to travel at 4 knots could go only 80 miles. Thus a U-boat could not travel very far under water before it had to come to the surface and stay there for a protracted period in order to recharge its batteries. In practice U-boats spent most of their time on the surface, submerging only when in the vicinity of a target, or in order to hide themselves from a patrolling aircraft or surface vessel. Nothing could have been further from the mark than an utterance attributed to Doenitz to the effect that the aeroplane could no more eliminate the submarine than a crow could fight a mole. One of the active counter-measures taken by Coastal Command was to institute air patrols over the areas in the Bay of Biscay through which the U-boats were in the habit of passing in order to reach the Atlantic. These patrols were sufficient to force the submarines to sub­ merge by day and charge their batteries by night. Some of the aircraft were fitted with the early 1.5 metre ASV, and the chance of one of these aircraft making a successful attack was much greater than for an aircraft relying on visual detection. By June 1942 a number of aircraft were also fitted with searchlights, known after their inventor (a serving officer) as Leigh Lights, and this meant that the U-boat was subject to attack by night as well as by day. Not only did the Bay patrols lead to the destruction of a significant number of U-boats, but

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they sufficiently interfered with the mobility of the remainder to reduce substantially their operational efficiency. The enemy’s answer was to equip the U-boats with listening receivers so that they could detect the approach of an ASV-fitted aircraft by the pulses that it emitted. By February 1943 sinking of allied ships in the Atlantic by U-boats had again reached an alarmingly high rate, and a combined naval and air effort was mounted to rectify the situation. In this effort Coastal Command played an essential part. Many more aircraft were now available and it was possible to patrol the Bay area day and night; moreover, they had much more efficient radar, operating on a wave­ length of 10 centimetres. The measures bore fruit and in July 1943 Coastal Command sank no fewer than 14 U-boats. After that the number of sightings began to fall off and in the month of September there was only one successful attack. This caused Coastal Command some considerable alarm. It had clearly been only a matter of time before the enemy would fit listening receivers working in the 10 centi­ metre waveband. At a meeting held at the end of October 1943, the Commander-in-Chief of Coastal Command stated that he was con­ vinced that the enemy had already done this and that the 10 centimetre ASV in its current form had seen its day. This conclusion was, however, premature. The Germans knew that the British had succeeded in mounting 10 centimetre radar in aircraft, since they had shot down a bomber so equipped in 1943. They were, however, not convinced that the striking results achieved by Coastal Command in finding surfaced submarines was as a result of using this equipment. It appears that they had experimented with 10 centimetre listening receivers, but had not heard anything; presumably the re­ ceivers were in some way inadequate for the task. The Germans, therefore, sought some other explanation of the great success attained by the RAF and came to attribute it to the fact that their own 1.5 metre listening receivers emitted, as receivers are apt to do, a small amount of radiation; they became convinced that RAF aircraft were fitted with apparatus that enabled them to detect this radiation and steer towards its source. It appears that they had been led to this view, or confirmed in it, by “duff gen” fed to them by an RAF officer whom they had taken prisoner. At any rate they wasted a great deal of effort in designing an improved 1.5 metre receiver with reduced radiation. In fact the falling off in the number of sightings of U-boats was a sign of success not of failure; U-boats were no longer being sighted because they were no longer making the direct passage across the Bay. However, even if the full facts had been known to Coastal Com-

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mand, it would not have made very much difference as far as the development of radar equipment was concerned. Sooner or later the enemy would develop efficient 10 cm. listening receivers and the effectiveness of 10 cm. ASV would be sharply reduced. A counter­ measure on our part was possible. This was to make a modification to the ASV transmitter so that the observer could reduce the power radiated as the target was approached. Since the radar pulse suffers attenuation twice, once on its way to the target and once on its return, the effect of this would be that as the aircraft approached the target the strength of the signal heard in a listening receiver would get less, not more. Unfortunately a cavity magnetron worked either at full power or not at all, and in order to reduce the amount of power radiated it was necessary to insert a somewhat complicated mechanical device, referred to as an attenuator, in the wave guide that conveyed power to the aerial system. At the beginning of 1944 a new model of 10 cm. ASV was ready for introduction. This was known as Mark VI and was a development of the earlier Mark III with a higher power transmitter and an atten­ uator. There was a crash program for the production and installation of 200 sets. I remember crawling over a Sunderland flying boat at Beaumaris on the Isle of Anglesey helping to decide details of a new installation. These installation conferences, along with periodical prog­ ress meetings at the Air Ministry, were a feature of my life at the time. Quite apart from the question of enemy counter-measures, 10 cm. ASV had had its day for a different reason, namely that 3 cm. equipment of far superior performance as regards resolution and range had been developed. Rather than spend a lot of effort on fitting attenuators to 10 cm. equipment it seemed better to press ahead with the installation of 3 cm. equipment. It was true that the 3 cm. equipment becoming available was not provided with attenuators, but its introduction would, at any rate, render listening by the enemy ineffective until such time as he could modify his receivers or provide new ones. There was, however, a political difficulty in securing the 3 cm. ASV, since the same or very similar equipment was used in Bomber Command under the name H2S, and there was a Cabinet ruling that the strategic air offensive should have priority. This was not a new problem for Coastal Command, which was used to having to compete with Bomber Com­ mand for its equipment, including its aircraft. In this instance it was ruled that Bomber Command should have first call on the British 3 cm. equipment, but that the American AN/APS15, which was to be known in the British service as ASV Mark X, should be available for

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Coastal Command when supplies began to come in. This was a sat­ isfactory solution, although Coastal Command felt some anxiety lest production or other difficulties should lead to undue delay. Fortunately this did not happen and, as the year went on, PDS became increasingly involved in the introduction of ASV Mark X into the service. We had already had experience of ASV Mark VIII which was the American ASD and operated on 10 cm. The various measures, including the ones just described, taken against the U-boats were successful. On 22 March 1944 Doenitz withdrew his U-boat fleet from a large part of the Atlantic, and in May abandoned all attempts at offensive operations against Atlantic convoys. U-boats continued to operate around the British coast and on the Arctic convoy route. The Germans brought the schnorkel into general use about the middle of 1944 and thereby regained the ability to move undetected. Many radar contacts with schnorkelling U-boats were reported, but post-war analysis has suggested that few of these can have been genuine and that the echoes must have come from blowing whales or from the incipient water-spouts known as “willywaws”. However, the con­ stant use of the schnorkel reduced the mobility of the U-boat to a great extent, and by the end of 1944 the naval forces operating against U-boats were so strong that once a U-boat had disclosed its presence by committing a hostile act it was in extreme danger of being destroyed. When submerged, a U-boat could receive radio messages on very long waves, but in order to transmit it had to come to the surface. At one period the U-boats had made surprisingly free use of radio for communicating both with the U-boat Command in France and with each other. They worked on the assumption that if they kept their transmissions short it would not be possible for their position to be fixed by means of radio direction finding. What they did not know was that the British had developed a shipbome cathode ray direction­ finder capable of working on very short bursts of transmission. With the aid of this it was possible for the position of U-boats to be plotted with some accuracy. The great success of the British cryptanalysts working at Bletchley in reading enemy signals, including signals passing to and from U-boats, was also a major factor in enabling the movements of the U-boats to be followed, as recent disclosures have made clear. According to an estimate made by the Operational Research Section at Coastal Command, it was possible to determine with 90 per cent certainty whether a convoy was being threatened or not. Although from the Allied point of view the U-boat situation was under control and did in fact remain so, there was plenty of cause for grave anxiety. Early in 1945 the Admiralty issued a seriously-

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worded memorandum on the subject. Post-war knowledge has con­ firmed that this anxiety was by no means misplaced. The U-boat fleet was increasing in size and new types, larger and with greater endurance, were on their way. No account of service at TRE would be complete without a reference to the famous Sunday Soviets. These were informal gatherings held from time to time on Sunday mornings in the Superintendent’s office, Sunday being with us a working day. Some particular aspect of the war with which the Establishment was concerned, or felt it should be concerned, came under review. The guests would be senior officers from the headquarters of one of the RAF commands or from the Air Ministry. They would meet selected members of the scientific staff, these being mostly senior people although often younger people with a particular knowledge of the area in question would be included. I frequently attended when matters relating to Coastal Command were being discussed. The Sunday Soviets are often quoted as an example of the happy relations that existed at the decision-making level between scientists and serving officers. As a result of these discussions, members of TRE would often come up with suggestions for meeting an oper­ ational need of which they would otherwise have been unaware. Before substantial manufacturing resources could be committed for a particular purpose, it was necessary that a formal requirement should be stated by the Air Staff. It was, however, widely recognized that many in­ novations originated within TRE and similar establishments, and that the formal stating of the requirement was merely the culmination of much discussion between people at all levels.

AIR DEFENCE EXPERIMENTAL ESTABLISHMENT, CHRISTCHURCH, HAMPSHIRE. T e l . N0S * H i g h c l i f f e i+ ll-I).12. TO THOR i t ray co n cer n . T he B e a r e r o f t h i s a u t h o r i t y

.... vffT. i s e n g a g e d on u r g e n t t r a s i n e s s o f t h e h i g h e s t p r i o r i t y i n c o n n e c tio n w ith t h e AIR DEFENCE OF GREAT BRITAIN. You a r e r e q u e s t e d t o g i v e him a l l n e c e s s a r y f a c i l i t i e s , a n d t o e x j ie d ite h i s r e t u r n t o h i s h e a d q u a r t e r s on c o m p le tio n o f h i s w ork. A l l e n q u i r i e s i n c o n n e c tio n w ith t h i s i n d i v i d u a l , o r r e p o r t s a b o u t h im , s h o u ld h e a d d r e s s e d t o m e, i f n e c e s s a r y , b y te le p h o n e . H is im m e d ia te d e s t i n a t i o n i s : .. . 7 ^ - . . .

________ • -------------------------------

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Ready for my first radar assignment

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11

A very early experimental 10 centimetre radar installation

12

The rotating receiver cabin of a GL Mk II anti-aircraft radar equipment on its wire netting mat

13 Inside the GL Mk II receiver cabin. The soldier has his hands on the crank that rotates the cabin

14 Relaxation in wartime. A garden party in the summer of 1943 at CAEE, Deganwy, North Wales. From left to right: myself, Lt. Col. David Linsay (Comman­ dant), and Major Turner of the Ministry of Supply

111

15 The first experimental mercury tank, with its associated electronic equipment. The tank itself consists of a steel tube 5 ft long with quartz crystals at each end. The tin cans containing the matching sections can be seen, with a coaxial cable emerging from the one on the right (summer 1947)

16

A posed group photograph taken late in 1947. From left to right: L. J. Foreman (kneeling), G. J. Stevens, T. Gold, myself, W. Renwick, P. J. Farmer, and S. A. Barton

17 “By this time most of the load was falling on Renwick”

18 A photograph of the EDSAC taken shortly after it began to work in May 1949

19 A family group taken in the summer of 1958 in the garden of the bungalow in Wellesboume, Worcestershire, where my mother and father were then living. Margaret is on my knee, and Helen and Anthony are sitting on the grass

20

Program testing hour on EDSAC 2, a typical scene in a computer room of the period (10 May 1960)

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SO U TH ERN GERM ANY

AUSTRIA

9 A trip to Germany

One day, when the Allied Forces had already penetrated deep into Germany, the civilian colleague with whom I shared a room in the RAF Officers’ Mess at Malvern turned up in uniform, explaining that he was about to go to Germany to investigate a scientific establishment that had been captured and to interrogate prisoners. This struck me as being a most interesting assignment, and I lost no time in mentioning to my superiors that if other similar opportunities arose I would be very glad to volunteer. And so it happened that in early June 1945 I went off to London to get some kit in preparation for a trip to Germany. While the War was still on, members of the scientific staff who needed to go to the Continent were given honorary commissions. This was not necessary now that the War was over and I could travel as a civilian. I wore an RAF battledress with the words “Special Duties” on the shoulder straps. I drew various other items, such as a water bottle, and bed roll. I was to travel with C. J. Carter, another TRE civilian, and we were given a somewhat minimal briefing by the officer in charge of these activities at TRE. Our instructions were to report to the headquarters of the Special Intelligence Section (known as T section) of the 6th Army Group which, we were told, was located at Munich. One would not expect an Army Group to be a difficult thing to find, and we set out full of hope from Hendon in a DC3 aircraft of the troop-carrier kind. It had continuous benches along both sides of the fuselage, and there was an arrangement for opening up a hole in the floor out of which the passengers could jump if their line of duty lay that way. We took off during the early part of the morning and travelled to Munich by way of Frankfurt and Heidelberg, where we landed briefly. It was a pity that no-one had mentioned to us that the 6th Army Group had moved to Heidelberg; if they had it would have saved us a good deal of time and trouble.

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There was another RAF party travelling in the same aircraft on a similar mission to ours. This was in charge of a Group Captain with whom we had made friends at Hendon. When we arrived at Munich, the Group Captain telephoned for transport and was duly promised it. None came, and he tried again with a similar result. It turned out later that on the first occasion he had spoken to someone at Heidelberg and on the second occasion to someone at Augsburg; no doubt transport had been sent to the local airport in each case. We were by this time feeling very hungry, since we had arrived at about two o’clock and it was now nearly seven. Fortunately, a medical Captain happened to turn up at that point and he offered us a lift to the Transit Mess, which he said was in the Hotel Excelsior. We ought to have tried to get there as soon as we arrived, on the principle that you make sure of your billet first, and report for duty afterwards. When we arrived at the Excelsior our orders were inspected and we were given rooms. Rarely have I enjoyed my dinner as much as I did that night. I remember particularly the strangeness of seeing really white bread after so many years of austerity feeding in England. We could not quite believe that the headquarters of T Section were not still in Munich, even if the Army Group as a whole had moved. Accordingly, the next morning we set out in a jeep to find it. When we got to the address we had been given, there was no doubt about its having moved along with the rest of the 6th Army Group. All that was left was a cheerful Canadian Major wearing the kilt of the Seaforth Highlanders. As far as we could see his main function was to guard a stock of “liberated” wine, but no doubt he had other duties as well. He cheered us up, gave us some advice as to how we might get transport and generously presented us with some bottles of the wine to take away. It would be pointless to give all the details, even if I could recall them, of the various telephone calls and journeys that we made that afternoon, but by evening we felt that we had the situation under control. We could, therefore, relax a little and look around at the strange world into which we had fallen. Germany was under Military Government and a curfew was in force. No German authority above the local level was recognized. No trains were running and there was no postal service. The extent of the bomb damage was far and away beyond anything that I had seen in England. One could drive a long way through the streets of Munich without seeing an undamaged building, and scarcely seeing one with a habitable room in it. The Excelsior Hotel was the least damaged building with the exception of the old Nazi party headquarters in the Konigsplatz which were of

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unusually heavy construction; the Braun Haus was in ruins. I saw two food shops open; there were no other shops open at all. By way of contrast, there were no shortages in the Excelsior Hotel. That Saturday night we had a party in one of the bedrooms. I do not remember who we all were, nor how we had come together, but the Group Captain was present, together with some of his colleagues; so was Carter and there was also a GI. One good thing that the American Army had done as a boost to morale (their own) was to get the Munich brewery working. We, therefore, had some beer that one of the party had collected; his story was that he had told them to send the invoice to Supreme Headquarters! Our own little party contributed the wine that the Seaforth Highlander had given to us and I think that the GI had some wine as well. Next morning things went relatively well. Some transport eventually turned up to take us to the local airstrip from whence we flew to Stuttgart. Here a most efficient adjutant gave us a jeep to take us to Heidelberg. The autobahn was in poor condition; many of the bridges were down and much of the surface was in a poor state. There were a great many women and children and a few men watching the traffic go by, but not the long streams of refugees and displaced persons that we were to see later. At Heidelberg we were soon fixed up with billets in the Hotel Victoria and went for dinner to the Senior Officers’ Mess in the Europa. Here all was very splendid and there was even a string band playing during dinner. We were not, however, to enjoy this luxury for long. When we located T section next morning and reported, we found that they had never heard of us, did not want us, and cursed the chair-bome officers in London who had sent us! It seemed that the best thing to do was to go to the headquarters of the 12th Army Group at Wiesbaden and see a certain Major JohnsonFerguson. We did the journey in the usual jeep. This was not the most comfortable of vehicles at the best of times, and I suffered agony from hay-fever which had hit me with more suddenness than usual because of my plunge to the south. We crossed the river Main on a ferry, propelled by four men, having barged our way to the front, ahead of a lot of German civilians who must have been waiting a long time; they made no complaint. The Major, who as his name suggests was British, heard our story and inspected our orders. He said he would try to speak to London on the telephone tomorrow; if this proved impossible, and in the absence of other instructions, he would on his own responsibility send us back to London in the afternoon. I fervently hoped that it would not come to this as I was beginning to enjoy myself. In the event,

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next morning London was inaudible and Major Johnson-Ferguson sent a signal about us asking for disposal instructions. He then gave us the day off. Wiesbaden had not been badly hit by bombing and was still a very pleasant spa town. The Officers’ Mess was in the Schwarzer Bock Hotel where it was possible to take a bath in the steaming hot water that comes out of the ground. There was plenty of wine to drink, and altogether we had a most agreeable time while the Major was deciding what to do with us. One afternoon we went to a bathing place in the hills overlooking the town from which there was a wonderful view down the valley of the Rhine. The reply to Major Johnson-Ferguson’s signal must have been sat­ isfactory because he told us that we were to go to the Supreme Head­ quarters of the Allied Expeditionary Force (SHAEF) at Frankfurt for fresh orders to regularize our position in the 12th Army Group, and that after that he would find work for us. SHAEF was housed in the I-G Farben building. This spectacular building, with gardens and an artificial lake, was almost undamaged, as though the allied staff had marked it out in advance for their own headquarters— although I do not believe that this was really the case. The sentries were crack American parachute troops, resplendent in smart uniforms with white gloves and scarves, looking, however, rather stifled in the heat. We saw a Captain who promised that our orders would be prepared and sent on the next day. One met all sorts of people in the Officers’ lounge at the Schwarzer Bock. I spoke to a British UNRA Officer who was concerned with the repatriation of prisoners. He told me that nearly a million Russians had been sent back to Russia in three weeks. British troops were coming out of the Russian occupied territories but not so fast; the French did not seem to be coming at all. The Poles were a problem. Some were quite happy to take Russian nationality, but others contrived to slip out of the camps and to wander at large in Germany, existing as best they could. Some of the Russians he said were by no means anxious to return home. I also talked to some Swiss officials whose car had broken down and who were making an unscheduled stop in the American zone. They were engaged in repatriation work and remarked that many displaced persons did not want to go back home, nor in some cases did they want to work. The International Red Cross had no access to the Russian occupied areas and my Swiss friends remarked on the fact that the Russians tended to look at things in an oriental way. The Swiss were very anxious to know about air-raid

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damage in England. I told them that I had thought it was bad enough until 1 had seen the damage in Germany. Our orders and clearances arrived the next morning. Major JohnsonFerguson said that he was sending us back to the Munich area to investigate some intelligence targets there. He gave us a short briefing and presented us with some chlorine tablets for purifying water and a supply of bug powder. He also gave us some practical advice, such as not to travel after 6 p.m. since there was still some danger of booby traps on the roads. We set out for Munich in a weapons-carrier and saw some more of the air-raid damage in Frankfurt. One could drive for twenty minutes and scarcely see an intact building. Our route took us through Wurzburg and Ingoldstadt and once we were outside the city of Frankfurt it became very pleasant. We passed through many attractive old German villages, a lot of them showing litde signs of the war. I particularly appreciated the descent into the town of Eichstatt on the Altmuhl. We spent the night at Ingoldstadt where there was a Divisional Head­ quarters. They fed us in their mess and billeted us in the local hotel where we had a large room with a tiled stove in the comer. It was here that I had my first view of the Danube. We saw many Germans in military uniform tramping home along the roads; the more fortunate ones had transport and the American Army was glad to give them petrol to help them on their way. There were also endless streams of civilians, men, women and children, some with their belongings in carts. What they had lost, where they were going, one could not tell; a pathetic aftermath of war. The next morning we drove to Freising, along rolling roads and through more picturesque villages. We reported to a Captain Thomas who was actually expecting us and had one or two targets for us in addition to the ones that Major Johnson-Ferguson had given us. We spent the remainder of the morning getting necessary clearances and set out in the afternoon for our first target, which was at Ismanning. We found it without much difficulty and interviewed the person con­ cerned. This was a successful beginning, although we were just a tiny bit deflated when we learned that Watson-Watt had been there before us. To my infinite relief my hay-fever had now subsided, and I could enjoy the smell of the sweet hay being carted along the roads in enormous loads and of the freshly cut timber in the pine woods. Some of the com in the fields looked nearly ripe, and everything depended on whether there would be enough labour available to get in the

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harvest. Travelling along the road from Munich to Wasserburg we caught sight of the Bavarian Alps, an irregular outline in the distance. The target that we were on our way to investigate had been described to us as consisting of a group of engineers located in a small village with some equipment. When we called at the Divisional Headquarters to report, we heard mention of a certain Colonel French who was said to be also investigating the target. Could this be, I wondered, the Johnnie French whom I had known as a somewhat colourful figure when I was at AORGP As soon as we arrived at the target, we sensed that there was something unusual afoot, and that the American major in charge was feeling uneasy about it. The group of engineers belonged to an electronics firm which had been evacuated hurriedly from the Baltic coast. Most of their effects and staff had arrived at the village, but some had been lost on the way. They were men with ruin staring them in the face, and they did not know what was going to happen to them. They were trying to make enough money to live by repairing broadcast receivers, and had a project for using their vacuum laboratory to repair vacuum tubes. We spent the afternoon talking to an engineer who had been working on some kind of steerable bomb with a television transmitter in it. When we were having dinner in the Officers’ Mess, in came Johnnie French himself, as large as life. It appeared that he had a plan to take the German we had been talking to back to England with him for further interrogation. Whether he had any real authority to do this I never discovered, but it gave me no surprise to find him engaged in this sort of adventure. He was on the point of persuading the American major to let the German go, and our sudden arrival, creating as it did a further complication, cannot have been welcome to him. However, we had obtained all the information that we needed and had no wish whatever to thwart Johnnie’s plan. Accordingly, we backed him up and I believe that he did, in fact, take the man to England a few days afterwards. The Germans we interrogated were very helpful and anxious to tell us all they knew. This indeed was to be our general experience. Many Germans were convinced that the Bridsh and Americans would soon be fighting the Russians and that our interest in their work arose from the fact that we hoped to make use of it and them in this new struggle. Back at Freising we wrote up our reports and then set out on our next trip which would take us into the Alps. We passed through Munich and observed that the town was gradually being cleaned up. We pushed on towards a little village near Rosenheim, not quite in

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the foothills of the Bavarian Alps. It did not take us long to find out what we wanted to know, and we spent the night with the Lieutenant commanding the local unit—a field artillery unit—in a small Schloss. Next day, which happened to be my 32nd birthday, we passed into Austria. The frontier had been obliterated after the Anschluss of March 1938; it was now marked again, but so far only by a noticeboard. Austria was popular with the troops since it was regarded as a liberated, not conquered, country and they were allowed to fraternize with the local people. The run through Austria could not have been more delightful. There were some signs of fighting having taken place but very much less on the whole than in Germany. Kufstein, just beyond the German border, looked more like a normal town than any that I had seen. The target was in an isolated place in hilly country, but we found it without difficulty. The group there were developing an electro­ magnetic gun, there having been a theory current in Germany that darts, fitted with contact fuses and projected by such a gun, would be an effective way of bringing down hostile aircraft. This group also had been evacuated. In fact, the reason why we were making this interesting tour was that, when the Baltic coast had become unhealthy, many German establishments and firms had been evacuated to Bavaria and Austria where they had managed to make themselves comfortable in country houses and other places. When we had finished our interrogation, we made for the 10th Divisional Headquarters at Garmisch. We passed over the Schamitz Pass (1180 metres), where we paused awhile to enjoy the view and eat a K-ration. K-rations were the staple food if you were on the move. They came in small packs each containing one meal and were of three varieties labelled breakfast, lunch, and dinner. They were quite ex­ cellent, although a certain monotony set in when one had been eating them for some time. They contained biscuits (crackers) instead of bread, and it was this perhaps that one most became tired of. At Garmisch we had a pleasant billet with characteristic views of the Alps and were fed in the divisional mess. The following morning, after a delay because our driver did not turn up —he was eventually found in his billet fast asleep—we set out to return to Freising. Our next investigation took us to Thuringia into an area that, ac­ cording to the Potsdam agreement, was to be in the Russian zone. By the fortune of war, however, it turned out that at the cease-fire the Americans were well beyond the line agreed. Accordingly, they were about to move back. This fact, which I did not learn until later, was to lend some urgency to the investigation. It started, however, by

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Carter and me setting out for Bad Kissingen for what we now regarded as a routine operation. We interviewed a German scientist who had been working on vacuum tubes and who was interested in cavity magnetrons. We then made tracks for Wiesbaden where we presented our report to Captain Boothwick, who had taken over from Major J ohnson-Ferguson. It was decided by superior authority that our German was sufficiendy interesting to be evacuated along with his equipment before the Rus­ sians moved in. Carter, who was anxious to return to England, left me at this point, and I set out by myself for Camp Dentine, not far from Kassel, to see a certain Major who was supposed to make the necessary arrangements. When I got there I found that no-one had heard of this Major. To make matters worse, the battalion which provided accommodation and transport for people like myself was moving out, and their relief had not yet arrived. I telephoned Wiesbaden and decided to relax until the situation cleared. The country round Dentine was nice, being hilly and wooded. After dinner I went for a walk along a path which wound up in the woods behind the camp; this was the first time I had been on anything approximating to a country walk while in Germany. I did not have to wait long for further instructions. At 2.30 p.m. the next day a message came through that I was to proceed not later than that day to a Division near Gehlberg, 10 miles south of Ohrdruf. The new battalion that had now taken over at Dentine gave me some transport on the strict condition that I was to send it straight back, and I set off. On the way we passed an endless stream of American Army traffic moving west. It was noticeable that there were very few civilians on the road, and I supposed that they had been warned off. One had become so accustomed to seeing innumerable small parties of civilians, with their belongings on their backs or in push carts, making their way as best they could. A few days earlier, near Gotha, it had been noticeable that they were all moving westward. The lucky ones had a horse or a donkey. One horse, carrying the belongings of a small party, had collapsed by the wayside and could go no further. This was one of those pathetic sights that brought home the whole misery of the situation. When I reported at the Divisional Headquarters I found that the Lieutenant-Colonel in charge of operations had had a signal about me. He fed me and sent me on without delay to the regiment con­ cerned. Here I found that all was in hand; I visited the site and did what was necessary.

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I was billeted in a house that had been occupied by American troops and was just being cleaned up. Everywhere there was a sense of imminent evacuation. Next morning, as I waited at the Regimental Headquarters for my transport, truck loads of troops were leaving. It would not have been nice to have been left behind. What the local population were feeling one can only imagine. As I stood out in the sunshine watching what was going on, I was approached by a German civilian, who said to me in English that he was an engineer and had come to offer his services to the Americans. He had with him a brief­ case no doubt containing his credentials. I was told that there was to be no regular handover at unit level to the incoming Russians. When the American Army had withdrawn the Russians would, later in the day, move in and take over. My transport from Division arrived at about 11.30. It turned out to be a comfortable staff car, an improvement on the jeeps and weaponcarriers to which I had become accustomed. I paid a final visit to my German, collected some further information and samples from him, and then set off for Wiesbaden. We passed through Ohrdruf which was where one of the more notorious concentration camps had been located. My driver claimed to have been in it shortly after it had been taken by men in his Division and had some horror stories to relate. The Officers’ lounge at Wiesbaden continued to be a good place to pick up information. Naturally there was much interest in the Rus­ sians and their attitudes. An American concerned with military gov­ ernment told me that one of the problems in the re-establishment of life in Germany was that it was divided by the impassable Russian barrier; they would not even let people communicate with their friends across it by megaphone. Obviously the Russians had begun in the way they intended to go on. All the brown coal and most of the food were on the Russian side. A British gunner Major on a visit from the British zone told me that a postal service for postcards only was being got going; beyond that there was no means of communication available to German civilians. They might, however, travel up to 100 kilometres if they could get the transport. On 4 July the Americans held a grand parade in celebration of Independence Day and I saw part of it. The Army was in fine form and very impressive. Moving about as I had been through the zone I was in a good position to appreciate this. American soldiers wore rubber-soled boots and, for anyone used to British troops, to see them marching was like watching a movie with the sound-track switched off.

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Looking through the hies of possible intelligence targets in the T section office, it became clear to me that radar had by this time been pretty well covered. There were, however, a number of reports of German war-time activity in ionosphere research that had not been investigated. Here was something that I could usefully undertake, and it would have the advantage of helping me to pick up the threads of my peacetime interests. Quite a lot of effort had been devoted to ionosphere research in Germany during the war. The object was to provide forecasts of radio propagation conditions. There were two distinct organizations, one run by the Reichpost and concerned mainly with the performance of commercial channels, and one run on behalf of the military. The latter had a research division under Dr W. Dieminger. Dieminger also had wide responsibilities for the coordination of ionospheric activities and for providing a forecasting and information service for the benefit of the military. I was taken aback at the extent of the research facilities that had been at Dieminger’s disposal. He had been able to establish a chain of five ionospheric observatories on approximately the same longitude running from Tromso in Norway, just inside the Arctic Circle, down to Syracusa in Sicily, with two other stations on a westeast line, near Paris and at Nikolajew in Russia respectively. These all reported by radio to Dieminger’s headquarters. The northern ones had facilities for observing the aurora while the others had facilities for observing the sun; all were equipped for making measurements of the earth’s magnetic held. In addition, under Dieminger’s control, there were three solar physics observatories situated on high peaks in the Alps. It was clear that Dieminger’s organization was pursuing a genuine research programme and not just making observations on which forecasts could be based. The Reichpost network of ionospheric observatories was not as widespread, although it included a station as far south as Rome. The German workers were, to a surprising extent, aware of work published in the British and American journals during the war. Diem­ inger immediately recognized my name when I mentioned it to him and produced a photo-copy of a paper of mine that was published in the Proceedings of the Royal Society in 1940. He was the only one of the Germans whom I met in 1945 that I kept sight of in later years. I visited him again on a later trip to Germany in 1948 when he was established at Lindau near Northeim. Many years later he attended a dinner given in London for my old supervisor Mr J. A. Ratcliffe in celebration of his 70th birthday.

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I found the investigation of German ionospheric research both worthwhile and interesting, and I worked quite hard at it, following up all the leads that I could get. On another plane, however, what I shall always remember of that period is the delight of driving about in Bavaria and Austria in the brilliant sunshine. For someone who had spent the entire war in the United Kingdom this was a release indeed, and I felt almost as though I were having a holiday at the expense of the government. I based myself on Freising and the trip took me both into new territory and into territory that was by now familiar. Particularly memorable was a visit to Salzburg and a drive on a lovely summer’s day to visit Dieminger at Ried, about 30 miles away in a roughly northerly direction. I was much taken by Salzburg and enjoyed walking about the old part of the city; there was very little traffic in the streets and not much war damage, except to the cathedral. When I revisited the city some 25 years later, I felt that much of the peace and charm had departed. By then the cathedral had been com­ pletely restored and, unless the modem visitor can read the Latin inscription on the west wall, he will be unaware that it was ever damaged. On my way back from Salzburg I had occasion to make a call in Berchtesgaden and took the opportunity of driving by Hitler’s house which had been severely hit from the air. That night I had a rather unsatisfactory billet at Rosenheim and the next night, determined to do better, I reported, somewhat unnecessarily, at Corps Headquarters at Tutzing on the Stambergsee. Here I had a room to myself in a hotel on a hill overlooking the lake; there was a marvellous view from my window, with the Alps in the background. My investigations next led me back to Garmisch where a new and comfortable Officers’ guest house had been opened since my last visit. One of Dieminger’s solar physics observatories was on the top of the Zugspitze which could be reached by a mountain railway running from near Garmisch. I determined to go up and see what there was to be seen. The Zugspitze is the highest mountain in Germany and rises to nearly 3,000 metres. The mountain railway going up it was being operated as a recreational facility for the troops. The train left the station in Garmisch at 10 o’clock in the morning and started off at a good rattling speed. However, after about a couple of miles a rack appeared in the middle of the rails and there began a slow grind up gradients of as much as one in four. The last three miles of the journey were through a tunnel cut out of the living rock; finally the train came to rest, and after taking a lift one emerged into brilliant sunshine amid snow and mountain peaks. The final 600 metres

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to the summit was accomplished in a cable railway. There was, as I had rather anticipated, little to see of the observatory, and so I de­ scended again with my interpreter to the lower level where we ate our K-rations. There was a hotel at this level where it was possible to get skis. My interpreter had lived as a boy in Austria and was anxious to be off into the snow. While he was enjoying himself I sunbathed and generally relaxed. The train left at 3 p.m. and we were back in Garmisch at 5.30. One my way back to Freising I visited the Herzogstand experimental station near Kochel. This is a famous site where Professor Zennech, one of the pioneers of radio, did his early experiments. It is situated halfway up the Herzogstand mountain at about 2,000 feet above sealevel; I remarked in my report that it was one of those places hard to reach on foot but possible in a jeep. The site was originally chosen for a long-wave station, the idea being to hang the aerial system between two adjacent hills. Initial tests, however, were disappointing and in any case short waves were coming into favour. I was told that Professor Zennech, then aged 74, was still actively interested in ion­ ospheric research. He was living in Augsburg, but unfortunately I did not get to see him. The organization he was connected with was very academic in character, and as late as 1943 was still publishing papers in the open literature. At Herzogstand they were interested in some of the outstanding problems of ionosphere research that I was well familiar with, for example, the anomalous summer-time behaviour of the F region. I had now completed what I set out to do, and accordingly made my way back to Frankfurt to write my report. This time I travelled by air. Flying was very informal at that time and, provided one had valid orders and the pilot was willing, one could hitch about Europe. A certain vigilance was necessary, and when we arrived at Frankfurt I only just retrieved my kit in time before the aircraft took off for Paris. I spent part of my time at Frankfurt working in my room in the hotel opposite the railway station where I was billeted and part in the offices of the organization to which I was attached. The state of affairs in Germany was changing noticeably. When I arrived the victorious Army was still intact and civil life was at a standstill. Now the Americans were busy reducing their Army to the size needed for occupation, and officers and men were disappearing overnight. The organization of the T Section office had consequently become chaotic and at one point Stephen Toulmin, whom I had known in Cambridge as a young philosophy student and who had the same status in Germany as myself, was left to manage things as best he could, a situation he

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accepted with cheerful resourcefulness. Civilian life was starting up again. The railways were beginning to come to life and there were posters in the Frankfurt station advertising the running of about 20 trains a day to places as far away as Wiesbaden and Darmstadt. Whether the supply of wine had run out, or whether the authorities had clamped down, I do not know, but this was the most abstemious week of my whole trip. It was, however, pleasant enough, and I met a number of my friends who were passing through, including Allen from the Cavendish with a party of people studying gunnery problems, and J. Comer who was on a somewhat similar mission. There was no chance of getting my report typed, since the only typist in the branch had just left for England. Accordingly I decided to go back to TRE and get it typed there. I managed to get a few cans of beer from the PX for a farewell party with Toulmin before leaving. There was difficulty about getting a direct flight to London, and I decided to go to Paris and hope for the best. It turned out to be very easy to get on an aircraft from there to London. We landed at Biggin Hill at about 4 o’clock in the afternoon, and set off in an RAF bus for central London. I had been in the American Zone for six weeks working and living with Americans. Back in London I missed the American voices around me. When I went to see an American movie the talk no longer had the artificiality of the screen, but was that of real people in real sur­ roundings. To be in the American zone had been more like being in America than in Germany, and I sometimes look back on that trip as though it had been my first visit to the United States. It was then that I began a love affair with America that has lasted the rest of my life.

10 Post-war reconstruction

As soon as the war in Europe was plainly entering its final phase I naturally began to think about my future. I was on leave of absence from my Faculty appointment in Cambridge, but it was by no means clear to me that my proper course would be to return to Cambridge and take up my life from the point at which I had left it six years earlier. I was then quite ignorant of the developments in digital com­ puting that were taking place in the United States and that I shall describe later in this chapter. If I had known about them I would have felt very differently. In early January 1945, when I was in Cambridge on leave, I called to see Professor W. L. Bragg, then head of the Cavendish Laboratory. I sounded him about the possibility of exchanging my University Dem­ onstratorship in the Mathematical Laboratory for one in the Cavendish, but he did not give me much encouragement. I saw him again in April and enquired about openings of which he might be aware in the industrial field, for I felt—and still do—that, while an academic career under the right circumstances is ideal, failing such a piece of luck, there is much to be said for industry. I followed up one suggestion that he made. He told me that Mr F. Twyman, of the optical firm of Hilger and Watts, was looking for a Director of Research. I called on Mr Twyman in my RAF uniform, just before I left for Germany. The job would not have suited me and nothing came of it; I mention it here mainly because of the coincidence that two years later I was to marry into the Twyman family. To all intents and purposes, however, my doubts about returning to Cambridge were resolved when, after seeing Bragg for the second time, I went by appointment to see Dr R. S. Stoneley who was then acting as Secretary of the Faculty Board of Mathematics. We were joined by another member of the Faculty Board, Professor W. V. D.

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Hodge. Hodge was also a member of the General Board of the Faculties, and therefore knew what was going on in the higher levels of the University. They received me very warmly indeed and it was on this occasion that I first became infected with the spirit of reconstruction and re-establishment of peacetime values that was to be the char­ acteristic feature of the immediate post-war years. Hodge explained that returning University Demonstrators were to be appointed tem­ porary University Lecturers for a period of three years in order that they might re-establish themselves. I would not be expected, as I had naively supposed, to come back with my original rank. Hodge and Stoneley obviously wanted me back and thus encouraged I ventured to make it clear that I would wish to be put in charge of the Math­ ematical Laboratory. Rather to my surprise Hodge responded in a positive manner to this statement. I had assumed that Lennard-Jones would wish to continue as part-time Director of the Laboratory as well as being Professor of Theoretical Chemistry. In fact, as I learned long afterwards, he had already made it clear that, in his view, it would not be in the best interests of the University for one person to occupy two positions in this way, and that the most satisfactory course would be for the University to appoint a full-time Director. The General Board of the Faculties appointed a committee to con­ sider what should be done. This committee held a meeting on 9 July 1945 and agreed to ask me to come to Cambridge to discuss the possibility of my taking temporary charge. Consequently, when I re­ turned to Malvern on 1 August after my trip to Germany, I found waiting for me a message from Mr J. T. Saunders, Secretary-General of the Faculties, asking me to telephone him. I lost no time in doing this and Saunders invited me to Cambridge to spend the night of 8 August in Christ’s College and to have discussions with himself, Hodge, and Stoneley on the following morning. If my recollection is not at fault we met in the Mathematical Lab­ oratory itself, by arrangement with Dr Shearer, who was in charge of the Ministry of Supply staff occupying the building. We discussed the things that would have to be done to bring the Laboratory into operation as a University Department and the offer made to me was that I should return to Cambridge with the rank of University Lecturer and be appointed acting Director of the Laboratory. For the latter responsibility I was to receive additional payment over and above the normal stipend of a University Lecturer. It was contemplated that the Mathematical Laboratory would have a certain amount of routine computing work to do for other departments and for research workers in Cambridge, but that its chief functions would be to take part in

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the development of new machines and new methods of computing and to provide for the instruction of students. It was characteristic of Saunders that, when he wrote to confirm these discussions a few days afterwards, he listed the things that were waiting to be done. The first was to secure access to the Laboratory, although this was a matter for the General Board rather than for me. I would be expected to lecture on numerical methods and the use of machines, and to make arrangements for bringing the use of such methods and machines to the notice of other Faculties. Desk calculating machines had all been requisitioned by the Government, but it was to be expected that an opportunity would soon occur to acquire ma­ chines and an estimate of cost would be required. Thought should also be given to the equipping of a workshop and the appointing of a suitably qualified assistant. There was also the question of my own release from war service. When the war in Europe ended, the Government adopted a cautious policy in regard to demobilizadon and the release of people engaged on war service. This was partly in order to avoid a disorderly transition to peacetime conditions, but also because the Far Eastern war still continued and no-one knew how long it would go on. However, Uni­ versities, and I believe other employers as well, could apply for the immediate release of members of their pre-war staff who were required back. The University had already made the necessary application in my case and it was expected that I would be released from TRE at the end of August. I wrote gratefully accepting the offer that had been made to me and began at once to see whether I could recruit a workshop assistant from among the TRE staff who would be looking for peacetime em­ ployment. One of the officers in the mess introduced me to Corporal P. F. Farmer, a man slightly younger than myself and due to be discharged from the RAF by Christmas. Farmer and I took to each other and after consulting Saunders about procedure and salary I offered him the job. I also got in touch with L. J. Comrie who had approached the University to see whether his firm, Scientific Computing Services, Ltd, could be of any assistance, particularly in regard to the supply of mathematical tables for the library. Comrie kindly invited me to spend the night with him in his home in Blackheath. I had been introduced to Comrie briefly at the British Association meeting in 1938, but this was my first serious meeting with him. He helped me in a number of ways, not only with regard to mathematical tables but also with the acquiring of calculating machines and the recruiting of staff. He was, at that time, an acknowledged authority on anything

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to do with computing. He was nearly 20 years older than I was and suffered under the severe handicap of having lost the lower part of his left leg when serving with the New Zealand Expeditionary Force in France in 1918. This disability he overcame admirably and I re­ member him cheerfully hopping about the house, having discarded the artificial limb that he normally wore in public. A more serious problem was his deafness which made conversation difficult. Comrie had first become known as Director of the Nautical Almanac Office where he had been responsible for bringing their computing methods up to date; when he first joined the office in 1925 they were still using logarithms! According, however, to his Royal Society biographer, the methods he adopted to reorganize the office were decidedly unorthodox from the Civil Service point of view and a break was inevitable. He resigned in 1936 to found Scientific Computing Services, Ltd, which set out to undertake computation on a commercial basis —a decidedly original idea for the time. When I arrived back in Cambridge at the beginning of September, the Ministry of Supply had been asked to release the Mathematical Laboratory by the end of that month. They did not do so, however, and in the middle of October it was reported to the General Board that they were not prepared to give up the Laboratory until they had constructed temporary accommodation elsewhere in Cambridge to house the staff. This was very discouraging, but fortunately it was discovered that the Laboratory had not been requisitioned under emergency legislation, but had been leased in the ordinary way. Notice to quit by the end of the year was therefore given. Nevertheless, I found towards the end of November that no preparations for evacuating the building were being made, and that Dr Shearer had not even been officially informed that he must go. The University were firm and insisted that the tenancy must end by 31 December, but as a com­ promise authorized me to allow the Ministry to retain some three or four rooms until the middle of January. In fact, they were all out by Saturday 5 January. How and from whom I first leamt of the significant developments in automatic computing that had taken place in the United States I cannot remember, but I do know that I obtained a great deal of information from Professor D. R. Hartree who worked in Manchester, but who was in the habit of visiting Cambridge from time to time. I had met him in 1937 when I went to see the differential analyser and on a few occasions during the war. Hartree’s name will recur ffequendy in this narrative.

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In 1946 Hartree was 49; he was, therefore, just old enough to have served in the First World War, during the latter part of which he worked on problems in anti-aircraft gunnery, then a new subject. After the war, he completed his education in Cambridge and went on to do research in physics. Wave mechanics was at that time in a state of rapid development and Hartree became interested in its application to atoms and molecules. He developed a technique, known as the method of the self-consistent held, for calculating approximate mo­ lecular wave functions by numerical methods. He became well known for this work which he pursued with great vigour. The calculations were performed on desk calculating machines, there being nothing else available. They constituted a remarkable demon­ stration of what it was possible to achieve, even at that period, by numerical methods applied systematically and with determination. It was natural that Hartree should go on to investigate other areas in which numerical methods could be exploited and it was as a specialist in these methods that he ultimately became known rather than as a physicist. As his reputation grew, many people would ask for his advice on numerical problems of all kinds. He was always ready to respond and would, as often as not, make a few trial calculations to test the soundness of the advice he gave. During the Second World War, Hartree remained in Manchester in charge of a group working with the differential analyser on various military problems under the auspices of the Ministry of Supply. Through the Ministry, Hartree was in touch with the developments in digital computers going on in the United States and in 1945, when the war in Europe was in its final stages, arrangements were made for him to pay an official visit to that country. The trip took place just after the European war was over. He visited Harvard and saw the Automatic Sequence Controlled Calculator in action. He also visited the Moore School of Electrical Engineering at the University of Pennsylvania, where he saw the ENIAC, then still incomplete. The Automatic Sequence Controlled Calculator was dedicated on 7 August 1944. It was the first large-scale fully automatic general purpose digital computer to be built. The ENIAC was even more significant in that it was the world’s first electronic computer. It was running during the summer of 1945, but was not formally dedicated until 15 February 1946. Although what had originally attracted me into computing had been the interest I felt in the differential analyser and other analogue ma­ chines that had appeared immediately before the war, experience had made me realise their limitations and how much patience and special

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skill was required to coax results out of them. In February 1946, I wrote a paper for the Faculty in which I referred to the development of new types of computing machine. I said “There is a big held here, especially in the application of electronic methods which have made great progress during the war and I think Cambridge should take its part in trying to catch up some of the lead the Americans have in this subject.” I stressed the merits of digital methods, but said that I still saw a future for analogue machines, provided that their range of application was sufficiently wide. Digital machines could be based on the use of mechanical counters, electro-magnetic relays, or electronic circuits. I said, “I would like to see a research student or a research assistant working in the Laboratory next year with the immediate aim of constructing a demonstration machine which will perform the op­ erations of arithmetic at reasonable speed and with as great a degree of simplicity as possible. I believe that certain electronic techniques used in radar could be applied to this problem.” I think that Hartree must have seen this paper and been struck by the disparity between the effort proposed and the objective to be attained. Fie came to see me specially to describe the great scale —and I remember his em­ phasizing those words—on which the American effort had been conducted. The scale of the ENIAC was indeed impressive. It contained over 18,000 vacuum tubes, occupied a room some 40 feet by 20 feet, and consumed 150 kW of power. It was an engineering tour de force in that the designers achieved their objectives by straightforward means, being undeterred by the amount of equipment required. Even while the machine was being built the designers, Presper Eckert and John Mauchly, began to realize that, by the application of logical principles and the adoption of a more subtle approach, there was a possibility that a computer of even greater power could be built with a fraction of the amount of equipment. Rumours of this had reached me, but I did not know anything of their detailed conclusions. In the middle of May 1946 I had a visit from L. J. Comrie who was just back from a trip to the United States. He put in my hands a document written by J. von Neumann on behalf of the group at the Moore School and entitled “Draft report on the EDVAC”. Comrie, who was spending the night at St John’s College, obligingly let me keep it until next morning. Now, I would have been able to take a xerox copy, but there were then no office copiers in existence and so I sat up late into the night reading the report. In it, clearly laid out, were the principles on which the development of the modem digital computer was to be based: the stored program with the same store for numbers and

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instructions, the serial execution of instructions, and the use of binary switching circuits for computation and control. I recognized this at once as the real thing, and from that time on never had any doubt as to the way computer development would go. The ENIAC was funded by the US Army as a wartime project and was subject to the usual military security. For some reason the draft EDVAC report was not given a security classification and a number of copies, including the one that Comrie showed me, were given away. I for one have every reason to be grateful that this happened. However, the fact that it bore von Neumann’s name only led to a grave injustice being done to Eckert and Mauchly, since many people have assumed that the ideas in the draft report were all von Neumann’s own. It is now clear that Eckert and Mauchly had advanced a substantial way in their thinking before von Neumann was given permission to visit the ENIAC project. The discussions that took place when he did so must have been very lively—indeed any discussion involving both von Neumann and Eckert could hardly fail to be—and speculation as to who produced this or that idea is bound to be unprofitable. Although the future might lie with electronic computers, in the short term the use of digital methods meant computing with desk calculating machines or punched-card accounting machines. This kind of com­ puting had made big strides during the war and the Admiralty Com­ puting Service, under J. A. Todd, and the Nautical Almanac Office, under D. H. Sadler, had shown what could be done with teams of computers —the word “computer” then meant a person, not a ma­ chine-under the direction of a competent numerical specialist. This experience, together with the prospect of rapid developments in elec­ tronic computing, had led to a proposal for the establishment in the U.K. of a National Mathematical Institute. This would have been an independent Establishment under the Department of Scientific and Industrial Research on a level with the National Physical Laboratory. Inevitably, this imaginative proposal had undergone progressive watering down and had finally been reduced to the setting up of a Mathematics Division within the National Physical Laboratory itself. This was in process of being organized at the end of 1945. In my memorandum of February 1946 I envisaged the possibility of the Mathematical Laboratory playing a similar role, although on a smaller scale, within the University. I had acquired a number of ordinary desk calculating machines and I was able to buy, second-hand, from Comrie a National 6-register accounting machine to be used for dif­ ferencing and sub-tabulation. I was also able, on Comrie’s suggestion, to attract to our staff Miss C. M. Mumford who had been trained by

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him as a computer and was, at that time, working for him. Miss Mumford brought a great deal of practical expertise, not only in the use of the National machine, but in desk computing generally. However, as things turned out, there was not to be a great demand in the University for professional computing with desk machines. This was not because of a lack of interest in computing, but because research students, for the most part, preferred to do it themselves. The Math­ ematical Laboratory became popular as a centre where desk machines and mathematical tables were available, and where professional as­ sistance and advice could be obtained when they were needed. It was, perhaps, just as well that I was not called upon to organize a desk machine computing service, since I would not have been well cut out for the part. I admired the skill and enthusiasm of the experts in the held, but unlike them I did not enjoy the labour of desk com­ putation nor did I regard numbers as my personal friends. For the same reason, I found more than a little tedious the usual texts on numerical analysis with their interminable case studies and discussion of this and that variant of a given method. I felt that the effect was to obscure, rather than illuminate, the underlying principles. Without knowing actually how it was to be done, I felt that the teaching of numerical analysis was in need of a shake-up. Many years later I did, in fact, publish a short introduction of my own to the subject. By then, however, the coming of digital computers had cleared the air and made it possible to see where some of the cobwebs lay.

11 Atmospheric oscillations

During the war I had, as far as circumstances would allow, kept up my interest in atmospheric physics. I had, in particular, studied the work that had been done by G. I. Taylor, C. L. Pekeris, and others on large scale oscilladons of the earth’s atmosphere. These oscillations are analogous to tides in the sea, except that they are induced by the thermal action of the sun as well as by the combined gravitational action of the sun and the moon. There was a theory, originating with Kelvin, that the atmosphere had a mechanical resonance with a period very near to 12 hours (solar time) and that this accounted both for the remarkable regularity over the earth’s surface of the solar semi­ diurnal variation of atmospheric pressure—as obtained by analysing barometric records —and also for the fact that the semi-diurnal variation is, in most places, distinctly larger than the diurnal variation. It was known by direct observation that the temperature in the atmosphere decreased with height up to the stratosphere, and then began to increase again until it was somewhat higher than at the surface of the ground. C. L. Pekeris had shown that in order for the atmosphere to have a resonance of the right period it was necessary for the temperature to decrease again as the height was further increased. It was this result that had originally led to my interest in atmospheric oscillations, since I had arrived at a similar conclusion from the studies that I had made of the propagation of long radio waves. As soon as the Ministry of Supply staff had moved out of the Mathematical Laboratory, and I had control over the differential an­ alyser, it seemed the obvious thing to use this machine to confirm Pekeris’ calculations. I invited Kenneth Weekes, who had been one of Appleton’s students and had returned to the Cavendish Laboratory after war service at the Royal Aircraft Establishment, to join me in this work. Weekes also had a long-standing interest in the subject,

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since in 1939 he had published with Appleton a paper giving clear evidence for the existence of a lunar tide in the lower ionosphere. Weekes and I duly confirmed Pekeris’ calculations using the dif­ ferential analyser, and obtained some additional numerical results. My Cavendish training had, however, made me unhappy with conclusions that emerged only after long calculations and I was glad when I was able to find a simple way of describing what was going on. The energy that sustained the oscillation was put into the atmosphere by the sun (either through gravitational or thermal action) near the surface of the earth and then travelled upwards. I showed that it was possible to present the theory in terms of the propagation of plane waves in a medium with a varying refractive index. The condition for the energy to be trapped, and hence for the atmosphere to have a resonant period, was that the refractive index should become negative at high level, and this implied a low temperature. I had an opportunity along with Weekes of presenting this work at a discussion meeting on atmospheric oscillations organised by the Royal Astronomical Society in London towards the end of January 1947. Appleton was in the chair and, no doubt partly because he was also a Cavendish man, my way of looking at things appealed to him. I had, perhaps, an unfair advantage, since the other speaker who dealt with the theory of atmospheric oscillations was G. I. Taylor. As far as this kind of physics was concerned, Taylor had no rivals, but his clarity of thought was not matched, at any rate on that afternoon, by clarity of exposition. For whatever reason, Appleton was complimen­ tary, and when two years later a little book that I had written on atmospheric oscillations came out he wrote me a most kind letter. I received one day an intimation that the Royal Society, on the recommendation of the committee concerned, had voted me a grant towards the cost of attending the General Assembly of the International Union of Geodesy and Geophysics to be held in Oslo at the end of August and the beginning of September 1948. This was the first large international scientific meeting that I had attended and it made a deep impression on me. I went by sea from Newcastle to Bergen in the M.S. Venus, the voyage taking about 24 hours, and then by rail to Oslo. This journey takes one through magnificent mountain scenery of great variety with a glimpse of a glacier at the highest point. The meeting of the Union was the first to have been held since the war. The last time that the Union had met in general assembly was in Washington in September 1939, and it had broken up prematurely on the outbreak of war. Participants from Germany and some other countries had, I believe, great difficulty in getting home. The meeting

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in Oslo was an important step towards the re-establishment of inter­ national collaboration. Such collaboration is desirable in many subjects, but it is essential in geophysics, because of the need that exists to conduct experiments and observations embracing a large part of the globe. The meeting in Oslo was well attended, although there were no participants from Germany and other ex-enemy countries, it having been considered impractical or impolitic to invite them. A leading personality in the affairs of the Union, particularly in those of the International Association for Atmospheric Electricity and Terrestrial Magnetism, which was one of its constituents, was Sydney Chapman, whom I have already mentioned in Chapter 2. Chapman was to become President of the Union six years later when it met in Rome. It was in Oslo that I first came to know him and to appreciate his remarkable qualities. There were sides to his character that would not be suspected by those who only saw him at formal sessions of the Union, or engaged in earnest technical discussion with other participants. Chapman lived an abstemious life and kept himself very fit. It was important to him to have a swim early every morning if it were at all possible; this was well known to those who entertained him in various countries and it sometimes provided them with a challenge. He was very fond of cycling and, when he had to go somewhere on business, he would often take his bicycle with him by train or boat and cycle the last 100 miles. In 1948 he had, I believe, cycled to Oslo from Stockholm, where he had been attending another conference. One of Chapman’s early achievements was to show that it is possible, even in medium latitudes, to detect the tide generated in the earth’s atmosphere by the moon. All that is necessary is to read the barometer once an hour—in fact, once every two hours will do —for forty years and then average the results! In tropical latitudes the lunar tide is much stronger and the job can be done with the aid of a few months’ observations. In his later years, Chapman remained scientifically very active, di­ viding his time between Boulder, Colorado, and College, Alaska. When he reached his eightieth birthday, his friends in those two places brought out a book to celebrate the event. All who had worked with him were asked for anecdotes. I recalled that he had early perceived the potential value of punched card equipment for lunar reductions and had succeeded in obtaining the loan of some. He was then faced with the problem of key punching. With characteristic resourcefulness, he approached the Commissioners for His Majesty’s Prisons and per­ suaded them to allow certain prisoners to do key punching as an

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alternative to sewing mailbags, which was then the regular form of hard labour in British prisons. It did not take me long to fall in love with Oslo. It enjoys the amenities of a capital city without being too large. In the summer the sun is brilliant and warm, in spite of the high latitude. A short tram ride takes one into the forests, which come down almost into the city. One of the attractions in Oslo Fiord is Amundsen’s famous ship the “Fram”, preserved in a specially constructed building. Wordie, who was also at the conference, had naturally a particular interest in this ship, and I very much wish that I had been able to visit it in his company. I have only once revisited Oslo —in 1961 —and I found then that it had in no way lost its charm. At the end of the conference there was an excursion by bus across country back to Bergen. We set out by train, transferring to buses to drive to Roysheim, where we spent the night in a tourist station. At dinner I sat by Professor Meinesz from Holland and Professor Bjerknes from Norway. Professor Bjerknes, who was well into his eighties, had been one of the leaders of the Norwegian school of meteorology which had developed the theory of the polar front. They talked about the German occupation of their countries and swapped stories one after the other about underground activities, clandestine radio sets, and other things of a darker hue. It was a side of the war that we in England had not met, and hearing them talk I began to realise why it had been thought too soon to have the Germans at Oslo. The more agile members of the party were offered the opportunity of climbing a mountain en route, and next day we left the bus at a strategic point and set off. Having been forewarned, I had taken with me a pair of stout boots, which as an additional precaution I had had nailed at a shop in Oslo. The mountain was Fannaraki, which was chosen because there was a meteorological station on the top. Since the Director of the Norwegian Meteorological Service was a member of our little party—we were ten in all and were referred to in a Bergen newspaper a day or two afterwards as the “upper ten” —we expected to be, and indeed were, well received. Norway was not too well supplied with food at that time, but there was no shortage that night, and our hosts had managed to secure some Scotch whisky, some French cognac, and some Havana cigars. We slept rather roughly in a hikers’ hut and had hoped to see the sun rise the next morning, but unfortunately it was cloudy. On the way up we had crossed a glacier, advancing in single hie and roped together, but whether this was necessary or was done to give local colour I do not know. I had managed to acquire a large-scale map of the area and it was interesting to see how the

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glacier had retreated since the map was made, thus bearing witness to the tendency that had existed then for at least fifty years for the climate of northern Europe to become milder. We descended the mountain by another route and in due course rejoined the bus. Weather forecasting in the countries bordering on the eastern Atlantic has always been handicapped by the paucity of information coming from the ocean. Accordingly, as a co-operative venture, a number of weather ships had been commissioned, and there were always several of these on station at strategic points in the Atlantic, from which they radioed back meteorological data. One of these ships, based on Norway, was at that time in home waters and was waiting for us at Balholm (Balestrand) to take us on the final stage of our journey to Bergen. The cruise through the famous Norwegian fiords was very memorable. The ship was appropriately enough named “The Polar Front”. During the course of the afternoon we passed through a small front and everyone rushed to observe the microbarograph in the cabin. Atmospheric oscillations became a major interest which I pursued for a good many years in parallel with the work on digital computers that I shall describe in the following chapters. Since computation played a part in the study of atmospheric oscillations both for the evaluation of theoretical models and for the reduction of barometric and geo­ magnetic observations, I was able, to a certain extent, to combine both interests. I attended subsequent Assemblies of the International Union of Geodesy and Geophysics held in Brussels in 1951 and in Rome in 1954, and I continued to publish occasional papers on at­ mospheric oscillations until the 1960s. By then a good deal of new information about the atmosphere had become available from ex­ periments with rockets and many of the old ideas were being upset. In particular the resonance theory that had at one time appeared to be well on the way to being firmly established was seen to be no longer tenable. Obviously a fresh approach to the subject was needed. For my own part, the computer field, which had gone ahead by leaps and bounds, was beginning to claim all my attention. With much regret, therefore, I dropped out of active participation in a subject which had received a major part of my attention over many years.

12 The Moore School

As a result of seeing the von Neumann report in May 1946 I was much better informed than I had been earlier in the year about the state of the computing art in the United States, but I was hardly in a position to plan a program of work. While I was thinking the matter over, I suddenly received a telegram from Dean Pender of the Moore School inviting me to attend a course on electronic computers that was to take place in Philadelphia during the period 8July to 31 August. This threw me into a state of some excitement and I hurried round to show Saunders the telegram. Obviously it was a wonderful op­ portunity. There was, of course, the question of funds. Saunders said that he might be able to persuade the General Board to give me a retrospective grant when I got back. Fortunately I had enough money in the bank and declared myself willing to take the chance. Saunders encouraged me with the remark “nothing venture nothing win”. In the end the total cost of the trip turned out to be about £200 and the Department of Scientific and Industrial Research came up with a grant of £150 towards it. There was also the problem of obtaining a passage across the Atlantic. Shipping was still tightly controlled by the Government and it was necessary to make application through the office of the University Grants Committee. I heard nothing for a long time and was beginning to despair when, on 23 July, I received a telephone call from someone in Whitehall who said that my application had only just arrived on his desk and would I like a passage on the Drakensberg Castle due to sail at the beginning of August. This was after the course had started and I should be late. After hesitating for no more than a fraction of a second I closed with the offer. The next move was to apply for an American visa. This involved some tedious waiting about at the Amer­ ican Embassy, but eventually the visa was issued and I was all set for the trip.

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Before leaving I ran into Hartree at a function in the Cavendish Laboratory. He had just returned from a second visit to the United States, this time of two months’ duration. The specific purpose of this visit was to discuss non-military uses of the ENIAC and he had been able to run on that machine a problem in fluid motion. He gave me much up-to-date information about computer developments in the United States and he also gave me a number of introductions to the leading people. I found these of great help when I was planning my own movements at the end of the Moore School course. At the time I spoke to him, Hartree had just accepted a Chair in Cambridge and was planning to take up the appointment at the beginning of October. I received instructions to report on Friday 2 August to the office of the shipping company in Gray’s Inn Road. There were not many people there and it appeared that the Drakensberg Castle was to carry only 35 passengers, all men. She was, in fact, a cargo vessel and in normal circumstances would have carried 12 passengers only. She carried no doctor and accordingly we were all given a brief medical examination (directed to ascertaining that there were no pregnant women concealed amongst us) at the shipping office. We then set off in a bus for the Victoria Docks and went straight aboard. I shared with two others a cabin originally intended for one, so we were a little crowded. It appeared that we were not due to sail until the next day at 5 p.m. It had originally been stated that the ship would go to Philadelphia, but a notice appeared saying that we were bound for New York. No one had any clear idea of when we might expect to arrive, since the Drakensberg Castle was on charter to Cunard from the Union Casde Line and this was her first crossing of the North Atlantic. We might have expected a crossing time of about eight days, but as I shall describe there were various troubles and it took us nearly twice as long. After leaving the dock we set off in fine style down the Thames. However at Gravesend or thereabouts we came to anchor. There was ominous talk of engine trouble and shore-based labour. I did my best not to think about how late I should be for the course. The weather was fine and hot and, if nothing else, I could enjoy the food. The end of the war had not brought any relaxation of food rationing in Britain— rather the contrary. Restaurant meals were very dull and limited strictly to three courses. As soon as we went aboard the Drakensberg Casde, even while we were still in the Victoria Docks, all this ceased to apply. Meat, eggs, cheese, and butter, all were plentiful, and four or five course dinners were the accepted thing.

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Sunday was a day of alarms and excursions, but on Monday morning I was woken by the steward with the news that we were moving. The weather was not very clear, but I thought I could just pick out the Dunkirk Chain station. We passed an anti-aircraft fort in the river similar to one that I had once inspected in the Mersey and were soon rounding the Nore. Unfortunately, it then appeared that we were not really on our way but were merely messing around adjusting the compass. At one time we appeared to be heading straight back for London and morale was low among the passengers. However, by the next day we had entered the English Channel and were steaming west. After having known the coast round Dover so well from the land, I was interested to see it from the sea, and I was able to pick out a number of landmarks. I began to find out how agreeable and relaxing life aboard ship could be, with plenty of good food, sea air, and no responsibility. Altogether the time went very pleasantly, including the daily walk about the promenade deck for exercise. I had brought with me the manuscript of my book on atmospheric oscillations and I found that I was able to do a small but useful amount of work on it each day, either in the smoking room or in my cabin. On about the seventh day out we encountered the Gulf Stream for the first time. The air became warm and sultry and there were frag­ ments of seaweed to be seen floating in the water. For the next few days we were in and out of the Gulf Stream and the temperature was apt to change suddenly and dramatically with, of course, accompanying fog. The ship was equipped with a 3 centimetre radar installation and, when I encountered the Captain one day just before dinner, I asked him how he found it. He said he was enthusiastic, but thought that the owners were inclined to regard it as just one more expense. He had made use of it in a patch of fog that morning and had been able to proceed without reducing speed. It was around this time that the engine trouble that had delayed us when leaving London reasserted itself, and one whole day we drifted helplessly with a black ball hoisted to the mast-head to indicate that we were out of control. Fortunately it was a dead calm day. The boat swayed gently and the trail in the water indicated that we were hardly drifting at all. The trouble apparently was not with the engines themselves but with the distillation equipment for feeding the boilers. As if to make up for the deficiencies of the Chief Engineer, the Chief Steward gave us a special dinner that night. Soon afterwards we were under way again.

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We entered New York harbour on the evening of Thursday 15 August after it was dark. I stood on deck by a Merchant Navy Officer, who was travelling as a passenger, and he pointed out to me the meaning of the various lights. We anchored in the quarantine area for the night and then turned in. Early next morning a doctor came aboard —he merely looked at me and asked me how I was —and the immigration authorities checked up on us. By 10.30 we were through customs and free to go about our affairs. I was given a lift into downtown New York by some fellow passengers, and I set about making my contacts. I had been told that the British Commonwealth Scientific Office in New York would help me with my return reservations, and on the Friday afternoon after landing I went along to see them. I got a very friendly welcome and while there telephoned the Moore School in Philadelphia and fixed up to join the course first thing on Monday morning. I was, of course, desperately late, there being only two weeks to go. There was no point in travelling to Philadelphia until the Sunday evening, and so I had a day and a half to look round New York, which was all very strange and exciting. I tried to get some cash at Barclay’s Overseas Branch near Wall Street, but found that New York banks were closed on Saturdays. The Cambridge branch had fixed me up with a letter of credit. This was an imposing document and had a kind of identity card called a Letter of Indication to go with it. I used my letter of credit successfully later on in Philadelphia but it was, even then, an old-fashioned way of taking money abroad, and most people used travellers’ cheques. In Philadelphia I put up at a hotel near to the University where a reservation had kindly been arranged for me by the Moore School. When I joined the course on Monday morning, it soon became abun­ dantly clear that I was not going to lose very much in consequence of having arrived late. The first month of the course had been largely given over to background material including a course of lectures by H. H. Goldstine on numerical analysis and the theory of partial dif­ ferential equations. When I arrived they were in the middle of studying the ENIAC in some detail with the aid of circuit diagrams or rather of cross sections, as they were called, of circuit diagrams, in which one example of each repeated circuit was shown. The class had been shown the ENIAC earlier and since I had missed this visit I was given a private view by Mauchly. It occupied a room some forty feet by twenty feet. The racks were built round three sides of this room, so that when inside one had the impression of being in a room within a room. Some of this interior space was taken up by punched card

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equipment used for input and output, and by three large function tables. These were large vertical panels on which were mounted some hundreds of switches on which numbers could be set. They played the same role in a computation as would be played by the mathematical tables used by a human computer. Function tables —or their equiv­ alent—with built-in aids for interpolation, were a feature of all the very early machines and represented a stage in the automation of computing in which it had not yet broken free from the practices of pre-automatic days. Later, when sufficiently large high-speed memories had become available, no special provision was made for tables, the numbers composing them being put into the memory like any other numbers. I spent some time with Mauchly going over the constructional details of the ENIAC but I was not offered, nor did I wish for, an opportunity of gaining practical experience of its operation, either from the en­ gineering or mathematical point of view. Indeed, the ENIAC was then regarded as already representing a stage of development that had passed, and it was taken for granted that future machines would be designed on the stored program principle. The basic principles of the stored program computer were easily grasped, but how they were to be implemented was, in the summer of 1946, an entirely virgin field. No systematic treatment was attempted in the course, but there were a number of lectures given by various people who each spoke about a particular design study. None of these studies was very complete, but taken together the lectures amounted to a pretty comprehensive canvassing of the various ideas then current. We heard about number systems, adders, complementers, multipliers, and a little about instruction sets and how to use them. One or two examples of subroutines for the evaluation of scalar products and matrix multiplication were given, but understandably enough, no at­ tempt was made to look forward to the subject of programming as one that would develop into a major art. The ENIAC had provided much experience in the use of vacuum tubes in switching circuits. The stored program principle, however, introduced an entirely new requirement, namely, one for a high speed memory capable of holding some hundreds of numbers at the very least and, ultimately, if computers were to be developed to their full potential, many thousands. It was, therefore, incumbent on Eckert and Mauchly, when putdng forward their proposals, to show that means existed whereby such a memory could be realized. Clearly, the use of vacuum tube flip-flops for storage on this scale would be out of the question. When drafting the EDVAC report, von Neumann,

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following the ideas of Eckert and Mauchly, adopted the concept of a delay memory. The existence was assumed of a delay unit into which a large number of pulses, say 500, could be fed before the first began to emerge at the output. Such a device could be made into a storage unit, capable of holding 500 pulses indefinitely, by connecting the output to the input, via suitable circuits for amplifying and regenerating the pulses. The pulses would be, as it were, trapped and would re­ circulate indefinitely. The addition of suitable circuits for inserting and extracting pulse trains representing numbers would be required. Al­ though it was nowhere so stated in the EDVAC report, the type of delay unit that Eckert and Mauchly had in mind depended on the transmission of ultrasonic pulses through a column of mercury. Sound travels in mercury at about 1400 metres per second so that a tube of mercury one metre long could contain about 1200 pulses, each with a total duration of one micro-second. Such tubes were referred to as mercury tanks in order to avoid confusion with vacuum tubes. Ultra­ sonic delay units had been experimented with in various radar lab­ oratories during the latter part of the war, but for an entirely different purpose, namely the cancellation of permanent echoes. It was known, therefore, that the construction of such units was feasible and there was no reason to doubt that they could be used as the basis for a computer memory. No-one had, however, demonstrated the contin­ uous circulation of pulses. It was comforting to feel that there was one way by which a high speed memory could undoubtedly be created given a certain amount of work. The disadvantages of the ultrasonic memory were, however, clear enough. Its access speed would be limited because of the time required for the pulses to come round, it would need complicated timing circuits for input and output and, since a good many tanks would be required to give a storage capacity of even a few hundred numbers, the amount of equipment required would not be small. We had, however, a further reason for feeling rather relaxed on the matter of storage. It appeared that the ideal device was just round the comer. This was the Selectron under development by J. A. Rajchman working at the RCA research laboratories at Princeton. The Selectron was an electron tube with a cylindrical electrode structure. It contained 4096 cells in each of which a binary digit could be stored. No scanning was involved so that all digits would be accessible in the same amount of time. Rajchman gave a characteristically optimistic lecture about this tube, being careful however to say that not all problems had been solved. He was then working on his third experimental tube and, according to a note I made at the time, he hoped to have 100 working

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tubes constructed by the end of the year. There were various references during the course to the possibility of storing information in the form of an electrostatic charge pattern on the back surface of the screen of a conventional cathode ray tube. The problem, of course, was that the charge would leak away and some form of regeneration would, therefore, be essential. It seemed that it would be necessary to have two tubes and to shuttle the information from one to another a good many times a second. There was no reference to the work going on in Manchester, of which I myself was at that time ignorant. Hartree had given me a letter of introduction to Professor Aiken and also one to Professor Caldwell of MIT, who was responsible for the differential analyser. I wrote to both these people with a view to visiting them after the course was over. Hartree had also told me that a project under the direction of von Neumann was to be set up at the Institute for Advanced Study in Princeton, and suggested that I should get in touch with Dr H. H. Goldstine who was joining it. Goldstine while a wartime army officer had been engaged on the ENIAC project at the Moore School. His contribution to the course that I was attending had been finished before I joined, and so I had not met him. It turned out that he was still living in Philadelphia and commuting to Princeton. He suggested that it would save me a journey if we met in Philadelphia and he invited me to dinner just as the course ended. It had already been decided that the machine to be built at Princeton should be a binary machine working on the stored program principle, and that it should be parallel rather than serial in operation. Goldstine explained to me the principal features of the design, including the device whereby the digits of the multiplier were put into the tail of the accumulator and shifted out as the least significant part of the product was shifted in. I expressed some admiration at the way the registers and shifting circuits were arranged —what a little later would have been referred to as the logical design—and Goldstine remarked that things of that nature came very easily to von Neumann. I arranged to travel to Boston overnight on 11 September, and this left me with a week to think things over and do a little sightseeing. It was, in fact, during this period that I first began to sketch out the design of the machine that finally became the EDSAC. Part of the time was taken up by a trip to Washington, where A. E. Smith, who was one of my fellow students on the course and who worked at the US Bureau of Ships, had invited me to spend a day or two with him in his apartment. This was mainly a sightseeing trip, but I did find time to call on L. V. Berkner at the Carnegie Institution of Washington

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where I had an interesting time talking about the physics of the upper atmosphere. In the train for Washington I met John Mauchly and we had a discussion about the future of computers. Eckert and Mauchly had decided not to stay on at the Moore School to participate in the development of the EDVAC, but to set up their own company to produce computers for sale. I am sometimes asked to what extent the handful of people who were engaged in early computer devel­ opment foresaw the way in which things would go. My answer is to say that, not only did Eckert and Mauchly and their associates at the Moore School fully appreciate the role that computers would come to play in the world, but they succeeded in communicating this under­ standing to those of us who were on the course. Although the emphasis on the course itself had been on scientific computing, there was no lack of appreciation of the potential importance of computers in business data processing and statistical work. In fact, we saw computers as coming to play a central role in both science and business. Whether, if we had ventured on a formal forecast, we would have been right as regards time scale I do not know. We would certainly have under­ estimated the time required to develop the first stored program com­ puters and the amount of electronic equipment that they would contain. We could, of course, have had no inkling of the fact that vacuum tubes would be displaced by transistors and certainly no premonition of the marvels that would be achieved with silicon chips. One question that Mauchly shot at me on the train was about the differential analyser. The Moore School had such a machine, con­ structed very much to Bush’s original design, except that the mechanical torque amplifiers had been replaced by electronic servo-systems. Mauchly asked me whether, in view of the development of electronic computers, I saw a future for that type of machine, remarking that some of his colleagues at the Moore School did. This was not a question that I had consciously considered, but I found myself saying no, and from that moment on I had no doubt in my mind that the days of analogue devices for scientific computation were numbered. I was to see more of Mauchly later that week since on his introduction I moved into some lodgings next door to the apartment that he occupied with his wife. I discovered that he also had interests in geomagnetic phenomena and atmospheric physics, and one night we talked about these subjects as well as about computers until late. It was at this point that there occurred a tragedy that even at this length of time I find it painful to record. John Mauchly and his wife had gone for a short holiday to the coast, and the weather being hot had thought to

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take a midnight bathe. By some mischance or misadventure Mary Mauchly got into difficulties and was drowned. On the day of the funeral I saw her little girl aged 7 playing outside the apartment, too young to realise what had happened. I travelled up to Boston on the overnight train on 11 September having booked an upper berth. This was a scene at once strange and yet so familiar from American movies. The berths were arranged on two sides of a corridor running through the centre of the car and one undressed as best one could behind heavy curtains. This was the ordinary way of travelling, an upper berth being slightly cheaper than a lower one. We steamed into South Station Boston in the early morn­ ing. I had had some instructions as to how to get to Aiken’s laboratory and I soon found a subway train labelled Harvard. The Automatic Sequence Controlled Calculator was located in the Cruft Building and Aiken received me kindly. The machine was working away in a very impressive manner. Aiken had a big project for the computation of Bessel functions and this, although I do not remember exactly, is probably what the machine was engaged on. In Aiken’s view the computing of mathematical tables for publication was a principal role for a digital computer, and he saw as a major difficulty that of arranging for publication of all the tables that would be produced. Results com­ puted by the Automatic Sequence Controlled Calculator were printed by directly coupled electric typewriters in a form suitable for photo­ graphic reproduction. Aiken remarked ruefully that they had caught one of the typewriters out in making a mistake and were fitting checking circuits. Aiken also showed me his Mark II machine—a relay machine— then in course of construction. Next morning I went to see Caldwell at MIT. The original differential analyser had suffered from many disadvantages, the principal ones being lack of flexibility when it came to changing the problem or altering scale factors, and lack of adequate means of obtaining a digital output. Bush and Caldwell had therefore set about designing an im­ proved version with electrical interconnection of the integrators and with electrically operated decade gearboxes. Setting up a problem was done through the agency of a punched paper tape. Compared with the original model this machine also had substantially improved ac­ curacy. As far as scale went it was certainly as impressive as the Automatic Sequence Controlled Calculator; it contained about 2000 vacuum tubes, several thousand relays, and about 150 motors. By the side of this machine the original one, on whose design our own had been based, looked puny indeed. As a matter of interest Caldwell took

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me through what had been the Radiation Laboratory—a large wooden building then no longer in use. It was here that much work on radar had been done during the war. I spent the weekend in Boston and was able to have a look round. I noticed, as all travellers do, that Boston is more like a European city than Philadelphia or New York. I admired the pleasant tree-shaded College Yard at Harvard, contrasting its mellow brick buildings with the heavy stone-faced buildings at MIT that put up, as I noted in my diary, a great show of pomp to the world. The British Commonwealth Scientific Office in New York, which had been so good to me on my arrival, had secured me a passage home in the Queen Mary sailing on 24 September from New York. There had been labour troubles in New York harbour that had given me cause for some anxiety, although it looked as though all had been settled. This, however, was not the case and on Monday 16 September I read in my morning paper at breakfast time that the Queen Mary would sail from Halifax, Nova Scotia instead of from New York. Strikes have now become an accepted hazard to travellers, but it may surprise some people to know that they started so soon after the war. I had very little idea of where Halifax was in relation to New York and I slipped into the Boston Public Library, just opposite the hotel where I was staying, to look at a map. I found that it would mean a journey of some 800 miles and I discovered later that it would put another $46 on to my expenses. However, in return I would see something of Canada, if only from the train. Going back to Philadelphia was almost like returning home, so attached had I become to that city. Initially I think it was the effect of moving out of a hotel into lodgings that had made me feel part of the place and not just a temporary visitor. However, I did not stay long before leaving for New York where I planned to spend a couple of days before I took the special boat train to Halifax. Those two days soon went in the usual sightseeing—a stroll round Central Park, a visit to the top of the Empire State Building, and some last minute shopping. An important side effect of the trip had been that I was able to stock up with clothes that were still rationed in England. I bought a number of presents including some nylon stockings, then a novelty; most of these were for Nina Twyman whose name will occur again in this record. To travel in the Queen Mary at that time was an experience that was rather out of the ordinary, since she had not yet been fully reconverted from her wartime state as a troop carrier. There was no division into classes and it was possible to walk right round the great promenade deck. The cabin that I occupied with three others was not

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very splendid but otherwise the amenities were first rate. I shared a table in the restaurant with Miss Elsa Shelley, authoress of “Pick-up Girl”, a successful play then about to be produced in London. One evening we were shown a film about the Queen Mary made up of pieces from newsreels produced at the time of her launching. These brought back memories of an earlier period of history which even then seemed long ago. The Queen Mary had been laid down just before the great depression of the 1930s and work on her was suspended. We were shown shots of the hull as it lay rusting for two years after two million pounds had already been spent. It was moving to see these pictures, with all that they implied and with a knowledge of all that had happened since, out in the middle of the Adantic in the vessel herself steaming along at 30 knots.

13 The EDSAC

I returned to Cambridge with my head full of thoughts for constructing a stored program computer of modest dimensions very much along the lines of the EDVAC proposal. I had spent some time roughing out the design in Philadelphia and on the Queen Mary, and I had formed a preliminary idea—hopelessly optimistic as it turned out— of the number of vacuum tubes that would be required. I had a great deal in my favour. I had returned to Cambridge as acting Director of the Mathematical Laboratory, with the brief of getting it going as a running concern. This I had successfully done, and from 1 October 1946 I had been formally appointed Director. As a result of Lennard-Jones’ foresight the Laboratory had the status of a University Department and its budget included money that could be spent on research at my discretion. As yet the staff comprised a handful of people only, but there was a clear intention on the part of the University that the Laboratory should develop into something significant. I could, therefore, embark on a project without the necessity of seeking approval or financial support from any outside body. Fur­ thermore, with my experience of radio and radar behind me, I was entirely confident in the design of electronic circuits and knew exactly what it was possible and what it was not possible to do with them. The only part of the proposed computer that would call for significant technological innovation was the memory. Here fate tossed me the ace needed to complete the master hand that she had already dealt me. Early in October 1946, I met T. Gold, then a research student in the Cavendish Laboratory, who had worked during the war at the Admiralty Signal Establishment on methods for the cancellation of permanent echoes in radar. During the course of this work, he had worked on the design of mercury tanks. He laid before my wondering eyes a dimensioned drawing of a mercury tank which he said would

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do the trick. I lost no time in having a tank built to this design and filled with mercury in the manner that Gold prescribed. It did not take long to put together, in an experimental fashion, the necessary circuits for feeding pulses into the tank. For amplifying the output pulses I was able to use a radar intermediate frequency amplifier, that I had acquired along with some other war surplus equipment. At first there was unwanted coupling between input and output and it was necessary to improve the screening. Once this had been done, the tank was found to work exactly as Gold had said it would. On 18 January 1947 I was able to measure the overall attenuation of the unit. This was 26 db. The tube containing the mercury was 1.5 metres long and the delay was about a millisecond. Although I could now feed pulses into one end of the mercury tank and take them out delayed at the other end, it was a little time before I succeeded in getting pulses to circulate indefinitely. At first, whenever I connected the output to the input, all the pulses would disappear. Eventually, however, I had the satisfaction of seeing a pattern of pulses permanently stored. The whole set-up was extremely touchy and very sensitive to interference; indeed the most convenient way of introducing pulses was to switch the room light on and off! The success or otherwise of the ultrasonic delay method of storage obviously depended on whether the sensitivity to interference could be reduced to such a level that patterns of pulses would circulate for long periods without becoming corrupted. There was no reason to believe that this would not be possible and indeed after I had rebuilt the equipment with proper matching and screening, and with the unnecessarily high gain radar amplifier replaced by a specially designed one with two stages only, I found that there was nothing to complain of in the storage properties of the system. This point, reached at the beginning of February, was a crucial one for the project; the soundness of the principles had now been established and the necessary data existed for the design to go ahead. Although there had never been any real technical grounds for doubting the soundness of the concept, some people could not believe that the mercury memory would ever work. Chief among these was Aiken who, having been a pioneer in one generation, was to prove an extreme reactionary in the next. He had visited Cambridge at the end of November 1946 and had been anxious to show us some slides of the Automatic Sequence Control Calculator. On the way back to the Mathematical Laboratory from the lecture room in which the slides had been shown, Aiken said to me, “You are not committed to the mercury memory, are you?” I was a little afraid of Aiken and I made

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the defensive reply that I was not committed to anything. I wish now that I had asked him to explain his objections in detail. I had just reached the point of beginning to check out an electrical prototype of the electronic circuits that were to be associated with each mercury tank when the country was hit by a fuel crisis. The coal mining industry had, for some time, been hard put to it to supply sufficient coal to the power stations and in February an unusually severe spell of frost and blizzard, such as had not been experienced for 100 years, brought things to a head. Severe restrictions were placed on the use of electricity for industrial and domestic purposes, and for a time the life of the country was virtually brought to a halt. I decided to cut a comer and skip some of the detailed checking that should have been done at that stage and to go ahead with the final prototype of what became known as Panel 1. This led to some difficulties later, since it turned out that the diodes that we had used for the switching circuits were unsuitable, and a retrospective change had to be made. It was at this time that I took what was perhaps the most farreaching decision of all, namely to design the machine to operate at a pulse rate of 0.5 Mc/s. I would have been entirely prepared—as indeed would any electronic engineer worth his salt—to accept the challenge of working at 1 Mc/s and this in fact was what most other designers of early machines using ultrasonic memories were doing. I had, however, other objects in view besides solving problems in elec­ tronic engineering. I wanted as soon as possible to feel what it was like to have an electronic computer and to experiment with the writing of programs to solve real problems, and I knew that the development would be much more straightforward at 0.5 Mc/s than at 1 Mc/s. I have never had occasion to regret this decision nor to doubt that it was the right one. Up to this point, apart from having Farmer and a junior laboratory assistant to do the mechanical construction and Gold to hold my hand in my first experiments with mercury tanks, I was on my own. However, the Department of Scientific and Industrial Research had agreed to provide the salary of an experienced electronic engineer, and Gold introduced me to W. Renwick, whom he had known at the Admiralty Signals Establishment. Renwick joined the staff at the beginning of March 1947, and from that time on we shared the work of designing and building the computer. G. J. Stevens joined us as an instrument maker in September and, a few weeks afterwards, S. A. Barton joined as an electronic technician. Both made a big contribution to the building of the EDSAC.

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I had other things to think about besides the EDSAC. Nina and I had planned to get married on 2 April, and there was a house to be bought and furnished and innumerable matters to be attended to. Setting up a house was not entirely straightforward at that epoch, when wartime shortages still continued. The only new furniture avail­ able was that manufactured according to certain government approved designs and sold under the name “utility”. The designs were good but the construction was rather flimsy. This furniture was allocated by a remarkable bureaucratic system of rationing. A newly married couple were entitled to an allocation of coupons, known as dockets; some of these could be spent at once and some in a year’s time. The immediate allocation posed a problem since it was sufficient to furnish either a bedroom or a sitting room but not both. Obviously the scheme had been worked out by a generation of civil servants used to living in bed-sitting rooms. Those who aspired to a higher way of life were thrown on their own resources. Fortunately, our parents weighed in with some gifts; the rest we bought on the second-hand market. The second lot of dockets became available too late to be of any real use. There was also a problem about common household articles which could quite well turn out to be unavailable. For example, an ordinary galvanized iron bucket was a thing of the past as far as the Cambridge shops were concerned. One afternoon Nina noticed a consignment of such buckets on a lorry driving into the town. She followed it, and was rewarded by seeing it draw up in front of a hardware shop. Early next morning she went to the shop and was able to secure the coveted bucket. We were very happy in the small house in the southern part of Cambridge in which we started our married life in 1947, but after our second child had been bom, we began to feel the need for some­ thing a little larger. We were lucky enough to find the ideal house on the other side of Cambridge, and we moved into it in 1952. It was there that we brought up our family—a boy and two girls —and it has remained our home until the present day. People have often assumed that the EDSAC was built from war surplus components. This was not the case; virtually all the components were new, being purchased either through ordinary trade channels or from a Government store that we were allowed to use. The vacuum tubes, or valves as they were called in Britain, were an exception. I was rung up one day by a genial benefactor in the Ministry of Supply who said that he had been charged with the disposal of surplus stocks, and what could he do for me. The result was that with the exception of a few special types we received a free gift of enough tubes to last

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the life of the machine. The supply position in the electronic industry was, however, far from good, and careful planning and advance or­ dering were necessary. Heater transformers, of which one was required for each chassis, were proving quite a problem when, by chance, I happened to run into a wartime friend who used to supply transformers to ADRDE and who was still in business in Christchurch. He took us under his wing, and after that we had no further trouble. A single mercury tank 1.5 metres long would hold only 16 words of 35 bits, and it was decided that, in order to give a reasonable amount of memory, 32 tanks would be required. Rather than build the tanks as individual units I conceived the idea of designing a battery, as I called it, that would contain 16 independent tanks. I took advantage of the fact that no practical work could go on during the fuel crisis and I set up a drawing board in my office. Problems of precision arose. The quartz crystals at the opposite ends of each tube had to be parallel to within a few minutes of arc, and all the tanks had to be of the same length to within a very small tolerance. I designed the batteries in such a way that, when the various pieces were bolted up together, these tolerances were met, there being no provision of any kind for adjustments. We had not the facilities in our own workshop for making anything on this scale and the construction of two batteries was therefore en­ trusted to the central workshops of the Engineering Department of the University. It was a great day when the first battery was delivered and preparations made for filling it. This was in the middle of December 1947. Things did not go quite smoothly. The design of the quartz crystal mountings was defective and some of the tanks did not work. This trouble was corrected fairly easily, but then it was found that there was some variation in delay from one tank to another. This was the result of an ill-judged attempt at economy. I had bought commercial grade mercury instead of the double distilled variety, thinking that the principal impurities could be removed by chemical cleaning, and that anything that remained was hardly likely to affect the velocity of propagation of sound. It soon became apparent that this was not the case, and that there were appreciable differences between samples of mercury taken from different bottles. There was nothing for it but to send the mercury back to be redistilled. When this had been done we had no further trouble. Gradually the computer began to take shape, as the local contractor that we were employing got into the swing of making the chassis. I tried to keep ahead by designing chassis that would be needed a few months ahead and giving them a preliminary test when they had been

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built. To Renwick, however, fell the main load of incorporating them in the growing machine and making them work. Often retrospective modifications to what had been built were necessary as further ex­ perience brought weaknesses to light. Eckert had made the remark in a lecture at the Moore School before I arrived that the ENIAC was designed in a considerable hurry. The same was true of the EDSAC. I computed that, if we had given the same attention to the design of the individual units as can be given to the design of a radar set or a television set, construction would have taken over twenty years. One had to cut comers and accept any unit that did its job even if one felt that the design was not optimal. Some of the units, such as the storage units (Panel 1), were repeated many times, but most of the units occurred in small numbers or were unique. The same circuits were, of course, used repeatedly on the panels but often with small changes, since we simply did not know enough at that time to achieve standardization. The EDSAC was like an early hand-built motor car in which parts were not interchangeable. The stage at which computers could be built from standardized and interchangeable plug-in units, each containing a number of gates and flip-flops, had not then been reached. In spite of the bad weather at the beginning of 1947, and continuing post-war shortages, we made surprisingly rapid progress. Towards the end of May 1947, following a short course of lectures that Hartree had given in the University, I gave a demonstration of pulses circulating in a mercury tank. By that time we had a rack half full of tested chassis. At that time I was busy designing a “half adder”. This occupied one chassis, and there were ultimately four of them in the machine altogether, two in the accumulator connected so as to constitute a full adder, one for counting words as they went by in a memory tank, and one for the program counter. I shall never forget the thrill I experienced when the half adder worked for the first time and I saw, on a cathode ray tube, the characteristic pattern of binary counting. I had had some difficulty in getting the half adder going and this made me realize that a circuit engineer coming to digital engineering for the first time had a few things to learn. In particular it was necessary to design the circuits so that they would handle transients correctly. In radar and television the waveforms could be treated as though they were recurrent, and this problem did not arise. I wondered how easy it was going to be to communicate the new know-how to other en­ gineers; in fact, when the time came, it spread like wildfire. Towards the end ofJuly 1947 we had a visit from Mr T. R. Thompson and a colleague from J. Lyons and Company, the caterers. Lyons had

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developed the practice of recruiting university graduates and training them for managerial duties at a time when this was rather unusual in British industry. They had a reputadon for being go-ahead and Thompson and his colleague had just come back from a tour of the United States where they had been on the look-out for new ideas. They had heard about digital computers and had at once perceived the value that these machines might have for business purposes. How­ ever, unlike others who saw computers as having value principally for large-scale record keeping in banks and insurance companies, Thomp­ son felt that they would have immediate application for the more mundane forms of business accountancy such as payroll preparation. He met various people in the United States who were working in the computer area, but none who could help his company acquire a ma­ chine within a reasonable time. One of the places that he visited was the Institute for Advanced Study at Princeton, and it was there that he learnt from Goldstine of our existence. Hence the visit. Thompson recalled later that I showed him some pulses on a cathode ray tube and remarked that I was not entirely satisfied with their shape. Although Thompson had had a scientific education—he had obtained a first class with a distinction in Schedule B in the Mathematical Tripos at Cambridge —he was no engineer, and comparing our pulses with some very inferior ones that he had seen at Princeton, he was led to ask the question “Are they too square?” However, it soon became clear both that we had created a good impression and that Lyons were serious about computers. On 11 November we had a visit from a deputation led by Mr G. C. Booth, a very senior and almost legendary figure in Lyons—at that time he was over 80—and including besides Mr Thompson and Mr H. H. G. Bennett. Mr Booth quickly came to the point. They would like to contribute to our funds to the extent of £3,000 and give us the services of an assistant for a year if we would in return undertake to put them in the way of constructing a computer for their own use. This was a most generous offer and I had no hesitation in accepting it at once. The sum may not sound a large one by modem standards, but it came at a moment when the natural growth of the project would have been checked if further money had not become available. Lyons were as good as their word. In a couple of days’ time I had the cheque, which I sent straight on to the University Treasurer, and an official announcement appeared in the University Reporter on 2 December. The custom was still main­ tained in those days of adding the names of those who made gifts to the list of benefactors of the University, and I think that it caused Lyons some surprise, but I hope also pleasure, when the name of

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their company was so added. The assistant that Lyons had promised us was Mr E. G. Lennaerts and he joined us without delay. He had been pulled off another project on which he was working, namely the automatic vending of sausages cooked, or rather re-heated, to a sizzling state by a diathermic furnace. He stayed with us for a lot more than the year originally contemplated and helped us a great deal. Later Lyons made him their maintenance manager. The connection between Lyons and Cambridge was strengthened when Lyons were joined byj. M. M. Pinkerton, who became the chief engineer of their computer project. Pinkerton, like so many of us, had worked on radar during the war, and was at the relevant time finishing his Ph.D. thesis at the Cavendish Laboratory. He was working under Ratcliffe on the physics of ultra-sonic wave propagation in liquids, and I had cultivated his acquaintance when I was designing the mercury batteries, although the tempo of the EDSAC project was such that I had to be careful not to be drawn into interesting physical byways. I was delighted when Pinkerton decided to accept the offer that Lyons made him, since I felt that the engineering side of their activities would then be in safe hands, and this indeed proved to be the case. While with Lyons, Pinkerton was responsible for the design of LEO 1 and also for the successor machines LEO 2 and LEO 3. In the years 1947 and 1948 the important thing was to press ahead with the project that had been started. The lines on which it should proceed were early determined, and no radical change was possible even if it had been desirable. We kept contact with other British groups working in the area, but they too were preoccupied with their own projects. From time to time information came through about the progress being made by groups in the United States, but we were not in close touch with them. Starting in April 1949, the United States Office of Naval Research began to issue a news letter which proved of great value as a channel of communication. When the EDSAC project was well under way I paid a visit to Manchester. Williams and Kilbum gave me a run-down of what they were doing and then asked how it compared with what we were doing. There was, of course, terminology apart, little difference except for the fundamental one that they were using a cathode ray tube memory instead of a mercury memory. The project at Manchester had, in fact, grown out of original research on the cathode ray tube memory initiated by Williams when still at TRE. Like everyone else who had considered the design of a memory based on a cathode ray tube, Williams realized that the pattern of charge used to store the information would need regeneration from time to time as leakage took place. The originality

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of his invention arose from the discovery that, during a regenerative scan, it was possible to determine whether a 0 or a 1 had been written at a particular place in sufficient time to enable it to be rewritten at the same place. It was possible, therefore, to use a single tube to store the information, instead of having to use two tubes and to shuttle the information from one to the other. Originally Williams was concerned to build equipment that would enable him to test this new system of storage, but when I visited him he was working on the design of a full-scale computer. At the end of the war C. G. Darwin, who had in 1938 resigned the Mastership of Christ’s College to become Director of the National Physical Laboratory, lost no time in setting up the new Mathematics Division. The head was J. R. Womersley who had been in charge of a Statistical Advisory Service at the Ministry of Supply, and E. T. Goodwin was head of the Numerical Analysis Section. Darwin’s in­ tention was that the new Division should take the lead in the devel­ opment of electronic computers, and he had persuaded A.M. Turing to join the staff. Turing had worked during the war at Bletchley where quite large-scale electronic equipment for use in breaking enemy codes had been developed. This was kept very secret at the time, and although I knew what the function of the establishment at Bletchley was, and that Turing had been there, I knew nothing more. Some information has recently been allowed to come out, and it appears that the equip­ ment was capable of scanning paper tape at 5000 rows per second and performing Boolean operations. Another person who had been at Bletchley was Dr A. W. M. Coombs, a Post Office engineer, who after the war returned to the Post Office Research Station at Dollis Hill, and was put in charge of the construction of a computer known as the MOSAIC for ADRDE. I remember being a little puzzled by the fact that he was not doing as much experimental work on circuit design as I would have thought necessary, and I once supposed that this was because of his experience at Bletchley. However, the Colossus, as the Bletchley machine was called, worked at a pulse repetition rate of only about 50 kilohertz and I now doubt the relevance of the experience as far as detailed circuit design was concerned. The ex­ perience did not in any case extend to mercury memories; here we were able to help by letting him have details of the design of our tank batteries and a number were built for the MOSAIC. Turing and I both took the Mathematical Tripos in 1934, but I do not have any clear recollection of him from those years. I cannot remember how and when I first met him after the war, but I do remember going to the first two of the series of lectures that he gave

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in the Ministry of Supply building in London at the end of 1946 and the beginning of 1947. In these lectures he outlined his ideas for the logical design of the Automatic Computing Engine (ACE), as the NPL computer was to be called. These ideas were quite different from anyone else’s. If, sometime in 1950, a new and superior type of memory had suddenly appeared in either Manchester or Cambridge, then it would have been possible —with somewhat of a struggle, since all digital engineering involved a struggle in those days—to connect it in place of the CRT or mercury memory. In either case the interface between the memory and the rest of the machine was such that the programmers would have known no difference. Not so with the ACE, which was predicated wholly on the mercury memory around which everything was built. The programmer juggled with a set of tank numbers and timing numbers in order to get pulse trains representing the various numbers to come together at the right place and to be in step. It was entirely in accordance with Turing’s turn of mind that programming for such a computer should have involved a knowledge of the way that the hardware was organized. I did not believe that computers would develop along the lines that Turing was advocating, and for this reason I stopped going to his lectures. A contributory cause was that he had aired his views on the engineering design of mercury memories, a subject well outside his sphere of competence, and had not received kindly the doubts I ven­ tured to express. Some time after joining the NPL in October 1945 Turing wrote a report endded “Proposals for Development in the Mathemadcs Division of an Automatic Computing Engine”. Turing states that the Report gives a fairly complete account of the proposed computer, but rec­ ommends that it be read in conjunction with the report that von Neumann had produced a little earlier. It is in many ways the more impressive report of the two, not so much for the detailed imple­ mentation that it proposes —this was along the lines of the lectures that I have already referred to—as for the vision it showed of the manipulative capability of the stored program computer. The time taken for a number or instruction to emerge from a mercury tank depended on where it happened to be, and a question facing the designer of any machine including a mercury memory was whether or not the programmer should be provided with facilities whereby he could put his orders and numbers in such places that they would come to hand just when they were required. This was known as optimum coding, and facilities for doing it were implicit in the design of the ACE. Clearly no perfect job could be done, but it was

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a fact that by going to some trouble the programmer could reduce the average access time to a significant degree. A similar situation existed some years later when magnetic drums were used for main memories. I took the view that it was only a matter of time before mercury memories would drop out and be replaced by truly random access memories. I argued, therefore, that in a situation in which there was obviously so much to be learnt about programming, it would be a mistake to divert effort into developing techniques which could only be of short-lived value. The EDSAC was, therefore, designed with no provision for optimum coding, and I still believe that this decision was the right one. The opposite argument was that computers with delay memories would be used for real computing, and that if they could be made to run two or three times as fast with no more complicated control circuits then why not do so? I have mentioned that I did not see eye to eye with Turing on computer architecture. He felt much about my proposals as I did about his. Hartree, who was a member of the executive committee of the NPL with special responsibility for the Mathematics Division, was anxious that we should collaborate, and had suggested to me that I might look to the NPL for financial support. Accordingly, in early December 1946 I sent Womersley a short note outlining in a somewhat minimal form the proposal for the EDSAC. The single address in­ struction code that I proposed—a first draft of the one eventually implemented in the EDSAC—would now strike people as being rather sparse, but otherwise unremarkable. Womersley referred my proposal to Turing, and the minute that he wrote about it has survived in a hie at the NPL. He remarked that the instruction code that I suggested was directly contrary to the line of development at the NPL, and much more in the American tradition of solving one’s difficulties by means of much equipment rather than by thought. He was also offended by the fact that I had not included any instructions for performing logical operations. Womersley did not send me a copy of Turing’s minute, but instead wrote a tactful letter giving its gist and suggesting a meeting. The EDSAC project was, however, by this time well under way, and it was becoming abundantly clear that it would be in everyone’s interest that we should proceed independently. The meeting therefore never took place. Turing did not stay very long at the NPL, and in 1948 he went to Manchester University where he became a Reader in the Department of Pure Mathematics presided over by Professor M. H. A. Newman. Newman had also been at Bletchley, where he had played a major role in the specification of the Colossus and its subsequent use as a

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cryptanalytic tool. Williams took good care that Turing did not meddle in the engineering design of the machine that he and Kilbum were building, but he did let him design the programming system, and this, as anyone knowing Turing would expect, made few concessions to the comfort of the user. Before going to Manchester, Turing spent a year at King’s College, Cambridge. I heard that he was there and I invited him to spend a morning at the Mathematical Laboratory so that I could show him what we were doing. After that, I used to meet him from time to time and always found him friendly, but I do not remember that we ever engaged in any deep technical conversation. The project for the construction of the ACE at the NPL did not go at all smoothly. Darwin had put in charge of it Dr H. A. Thomas, who had done good service on the design of radiosondes and similar devices and whose current interest was in industrial electronics. He was more confident than informed on the subject of computers, and under his regime the project did not prosper. It was eventually rescued most effectively by F. M. Colebrook, who was an old ionosphere friend of mine, and who had helped to settle the Stenode Radiostat contro­ versy. Colebrook assembled a keen team, pardy composed of engineers and pardy of members of the Mathemadcs Division who were prepared to take off their coats and become engineers or even wiremen for the time being. He decided to concentrate on a small model of the ACE that had already been designed in outline, and this machine, known as the Pilot ACE, was running in the summer of 1950. The design reflected strongly Turing’s ideas, although it did not follow them in all their purity, and I think that the decision to go ahead with a scaled down project was unwelcome to Turing. A prominent member of the Pilot ACE team was J. H. Wilkinson, who was later to use the machine to good effect in developing methods for the numerical solution of problems in linear algebra. When Hartree visited the Moore School in 1945 he met there Harry D. Huskey who expressed an interest in working in England. Hartree was able to arrange for him to spend the year 1947 at the NPL. While there he contributed significantly to the design of the Pilot ACE. I got to know Huskey quite well and I realized what a tower of strength he would be if I could persuade him to join the EDSAC project. Accordingly, when his time at the NPL was drawing to an end, I approached him to see whether he would be interested in working in Cambridge for a year or two before finally returning home to the United States. I got a distinctly positive response. However, Huskey had accepted an offer to join the staff at the National Bureau of

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Standards and they were very anxious to have him by the agreed date. Accordingly he was not able to accept my offer. Huskey’s involvement with the Bureau of Standards turned out to be very fruitful. He was sent to the Institute for Numerical Analysis operated by the Bureau of Standards on the campus of UCLA, and was there responsible for the design and construction of the SWAC computer. Thus Huskey himself and the computer held lost nothing by his not joining our project—indeed the contrary—but I have often wondered what difference it would have made to the early history of the subject if Huskey’s energies and abilities had been applied to the EDSAC instead of to the SWAC. In 1947 we had plenty of visitors to the Laboratory who wished to hnd out what this new subject of computers was all about, but there were very few people who were already sufficiently informed for it to be possible to discuss technical issues with them on equal terms. I was, therefore, particularly glad when one day in February 1947 I had a visit from A. D. Booth of Birkbeck College, London. Booth knew the whole story, having spent a period working at the Institute for Advanced Study in Princeton. He was busy designing a relay computer that would be unusual in that it would operate on the stored program principle and work in the scale of 2. Booth became a constant visitor to the Laboratory, and I saw him from time to time at Birkbeck. He was unfortunate in being severely handicapped by lack of adequate funding. I remember visiting him early in December 1948 and seeing a demonstration of a magnetic drum memory. The possibility of using drums for storage purposes had been mentioned by Eckert during the Moore School Course, but Booth’s demonstration was the first that I saw. He had, I think, only one track working, but he was able to demonstrate on an oscilloscope the writing and reading of digits. As the EDSAC project gathered momentum I began to feel the need for more help with documentation and with the numerous prob­ lems, partly technical and partly administrative, that go with any largescale project. I had begun to make enquiries when one day I ran into a former TRE colleague who told me that E. N. Mutch, who had been my principal aide when I worked at TRE and who had stayed on with the Establishment, was thinking about making a move. I lost no time in getting in touch with him. The government establishments were busy reorganising themselves on to a peacetime footing. They had made Mutch an offer of a permanent post, but at a salary below his current one; perhaps they did not appreciate his qualities as much as I did, or perhaps they had no real alternative, since a substantial cutting down from wartime strength was inevitable. However, Mutch was

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glad to join us, and the association that we then resumed continued until his death in 1969. He was a man of great parts, and I came to rely very heavily on him. At about the same time our first research student joined the Lab­ oratory. This was J. M. Bennett, now Professor of Computer Science at the University of Sydney; he was a Queenslander by origin and was working for an electrical company in Australia when he heard a radio talk on the developments that were taking place in automatic computing. This roused his interest and he wrote to Professor Willis Jackson at Imperial College, London, to make enquiries. His letter happened to arrive when Hartree was visiting. Jackson handed the letter to him, and he in turn passed it on to me. Now that the Laboratory was growing and we had a research student, with the prospect of having more, I thought that the time had come to start holding a regular series of colloquia, or seminars as they would now be called. All active university research groups had such meetings and I well remembered how valuable those organized by Ratcliffe had been to me when I was a research student and after. The first talk was about programming for the EDSAC —then a subject hardly ex­ plored—and was given by Ben Noble who had recently joined the staff to take charge of the differential analyser and the Mallock machine. I sent copies of the notice to some of our friends outside Cambridge and was gratified and rather surprised to find that some of them turned up. Thus started a series of more than domestic importance. Few opportunities then existed for those actively working on computers to meet and discuss their problems and for those who were outside the charmed circle it was extremely difficult to get information. The Cambridge colloquia served the purposes of both these groups, and as time went on the number who attended more or less regularly grew. The meetings began at 2.15 in the afternoon, normally on Thursdays, and tea was provided afterwards in the Laboratory. A fairly frequent visitor was C. G. Holland-Martin, of the British Tabulating Machine Company, who kept a close eye on what was going on in the Laboratory, and we were always glad to see him. I have a very clear recollection of a visit he paid in the latter part of 1948 or the early part of 1949 when the EDSAC was in an advanced stage of construction. At that time the mercury batteries were accom­ modated in wooden boxes—known colloquially as coffins—placed behind the racks containing the corresponding electronic equipment. We were sitting on one of these coffins and I had been going into various technical details. We fell silent, and I realized that he was trying to make up his mind whether this enterprise was a mad university

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escapade or whether it heralded the world to come; in more immediate terms what, if anything, his company should do about it. At the time we started to build the EDSAC, punched card machinery of the Hollerith type was marketed in the United Kingdom by the British Tabulating Machine Company (BTM). This Company worked closely with IBM—not then the mammoth corporation that it has since become—with whom it had a long-standing agreement dating from before the First World War. This gave BTM exclusive marketing rights in the British Empire with the exception of Canada. In October 1949, the agreement was abrogated by mutual consent. The agreement had been very favourable to IBM, who received a very substantial royalty on the sales revenue. Punches were excluded and a difference of opinion arose as to the interpretation of this term, BTM claiming that it included multiplying punches. IBM held no equity in BTM, but at the time of the separation received a sum of money—I believe some £60,000—in respect of certain rights. I was not very surprised to receive the news that BTM and IBM had parted company, since, a litde while before Holland-Martin, who had just returned from a visit to the United States, had told me that IBM had been unwilling to let him see certain new developments that they had in hand, although on a previous visit they had shown him everything. The effect of the change was that IBM found themselves without a foothold in Britain. For a time, Mr Swann, a London patent agent, attended our colloquia fairly regularly on their behalf. Although our contacts with BTM on the subject of digital computers were limited to conversations of the type recorded above, the company was very generous to the Laboratory in another connection. For many years, while at Imperial College, Professor Sydney Chapman had put much effort into the analysis of barometric and geomagnetic obser­ vations for periodic lunar variations, using punched card equipment provided without charge by BTM. When Chapman left Imperial College in 1946 to go to Oxford, he suggested to me that I might like to carry the work on in Cambridge. I agreed to this and, through his good offices, BTM agreed to lend us the necessary equipment; secondary motives on my part were to get some experience of punched card computing and to have the equipment available for possible other uses. Kenneth Weekes and I spent a lot of time on lunar reductions, both of atmospheric data and of geomagnetic data, although I came eventually to realize that the law of diminishing returns for the particular type of analysis we were undertaking had begun to operate. Perhaps the most important secondary use of the punched card equipment was to provide a computing service for the X-ray crystallographic

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group under Dr W. H. Taylor at the Cavendish Laboratory. We were able to set up a simple but effective system for Fourier synthesis that met their requirements for some years. The development of the EDSAC was punctuated by a series of landmarks. The first of these was the successful demonstration of patterns of pulses circulating in the mercury tank and remaining un­ changed for hours at a stretch. Next came the demonstration of binary counting and, after that, success with the filling of the first tank battery. As time went on larger units of the machine, notably the multiplier, were made to work, and eventually the point was reached at which an instruction could be executed from memory. These landmarks we celebrated by a journey to the local pub —known as the Bun Shop— where I would treat my colleagues to a pint of beer. Everyone was included. Stevens is fond of recalling how, to his great surprise, he was swept off to the Bun Shop for such a celebration at the end of his first week as an instrument maker. By the autumn all the principal parts of the machine were working separately and the input tape reader had been attached. In February 1949 it was possible to read instructions from the input tape into the memory and shortly afterwards an output teleprinter was attached. Then followed a period of several months during which the timing of the various parts of the machine was adjusted, logical errors in the design were weeded out, and circuit improvements made where they were found to be necessary. This was an anxious period. The process of checking out a new computer design is now well understood and due allowance is made for it. Then, we were learning as we went along, improvising our test methods and procedures. By this time most of the load was falling on Renwick. I felt that he was making steady progress. Finally, and rather suddenly, on 6 May 1949, the machine read in a program tape for computing a table of squares and printed the results. David Wheeler immediately set about writing a program for computing prime numbers and a day or two later this program had also run.

14 First steps in program m ing

There was much spade work to be done in order to turn a raw computer into a useful computing tool. Even simple things like reading in decimal numbers and converting them to binary form needed a non-trivial program or subroutine. As soon as the EDSAC began to work I called a meeting of those interested in the development of programming methods —it would have been premature to call them programmers —and we constituted ourselves into a committee to es­ tablish a library of such subroutines in order that every user should not have to start from the bottom. At first we thought of the library as containing subroutines of the type just mentioned and subroutines for the computation of elementary functions; later it became clear that it could be expanded in various directions, notably by the inclusion of subroutines for performing some of the standard operations of numerical analysis. It was so clear to me that we should base our system of programming on a library of subroutines that I was somewhat surprised a few years later to find that not everyone had gone this way. Fortunately, just when it was needed, the project had received powerful reinforcement in the person of David J. Wheeler, whom I mentioned at the end of the last chapter. Wheeler joined as a research student in September 1948. He had previously been one of a group of undergraduates who had volunteered to give a hand with some of the constructional work on the EDSAC during the vacation and was therefore well informed about the project. I suggested to him that he should imagine that the EDSAC was completed and consider how it should be used. He took this hint with such effect that when the time came he was several steps ahead of the rest of us in his thinking. Wheeler’s first contribution was to write the initial orders which were to be wired on to a mechanical read-only memory consisting of

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a group of uniselectors. Their purpose was to get the reading of the program tape under way. The initial orders were wired on to the uniselectors early in 1949 and they played a major role in the com­ missioning of the machine. The EDSAC began to work just in time to be demonstrated at a conference on high-speed automatic calculating machines that was held in Cambridge from 22 to 25 June. This conference was originally conceived as being in the nature of an extended colloquium, the regular colloquia held in the Laboratory on Thursday afternoons in the Laboratory having proved so successful. However, we were agree­ ably surprised at the extent of the interest aroused. Altogether, including local participants, about 100 people attended. A number of my wartime associates were there including Colonel Paterson, who was still at the Ministry of Supply, and Brigadier G. H. Hinde, who had commanded CAEE during the latter part of the war and was now also at the Ministry of Supply. Brigadier Hinde had a responsibility for research and development and had taken a keen interest in what was going on in Cambridge. He sent along two of his officers who made themselves responsible for the preparation of the conference report, which was then printed by the Ministry of Supply; all we had to do was to distribute it. This report, which has recently been re-issued in facsimile by the Laboratory, gives a very interesting snapshot of the state of the art at the time. Professor A. Walther came over from Darmstadt for the conference, as did A. van Wijngaarden from Amsterdam. We also had G. Kjellberg from Sweden, where a Board for Computing Machinery had been established. There were several other foreign participants and the conference may be claimed as the first European computing conference. The EDSAC was demonstrated on the first day. Wheeler’s program for calculating primes was run, and also one written by me for tabulating squares and their differences. The latter, of course, involved a trivial computation, but I had taken some trouble with the layout and had programmed the machine to suppress leading zeros. Attention to points of this kind became a feature of the Cambridge school of automatic computing. Wheeler discussed the various problems that were involved in the establishment of a library of subroutines intended to be stored on paper tape and copied mechanically on to program tapes as required. Since a given subroutine would not always go into the same place in the computer memory, adjustments to some of the addresses in it were required (what is now known as relocation) and Wheeler showed how this could be done by a sequence of what he called co-ordinating orders which could be copied at the beginning of every program tape.

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Other computer groups were well represented. In particular we had F. C. Williams, T. Kilbum, and M. H. A. Newman from Manchester University. Williams spoke on cathode ray tube storage and Kilbum on the current state of the machine being built at Manchester University. He described the miniature machine demonstrated a year earlier that had 32 words of storage, facilities for subtraction only, and a set of keys for input. Their current machine was a development of the min­ iature machine with full arithmetic and logical facilities in the accu­ mulator, a B register (this was the original name for an index register, which was a Manchester innovation), and a magnetic drum. Plans for immediate future development included the provision of more B reg­ isters, improved input and output facilities, extension of the capacity of the high-speed memory and the magnetic drum, and the provision of arrangements for automatic interchange of information between them. By June 1949 people had begun to realize that it was not so easy to get a program right as had at one time appeared. I well remember when this realization first came on me with full force. The EDSAC was on the top floor of the building and the tape-punching and editing equipment one floor below on a gallery that ran round the room in which the differential analyser was installed. I was trying to get working my first non-trivial program, which was one for the numerical inte­ gration of Airy’s differential equation. It was on one of my journeys between the EDSAC room and the punching equipment that “hesitating at the angles of stairs” the realization came over me with full force that a good part of the remainder of my life was going to be spent in finding errors in my own programs. Turing had evidently realized this too, for he spoke at the conference on “checking a large routine”. Like most people who have discussed the same subject more recently he took as an example a trivial routine, namely, one for calculating a factorial without the use of a hardware multiplier. It would enhance Turing’s reputation if I could state that he did in some way anticipate the contribution that Floyd made many years later. This I cannot do, although Turing did use the word “assertion” and he did point out the separate need to show that the execution of the program would terminate. What was missing was the concept of the loop invariant; if he had had the concept, he would have had no difficulty in giving the value of the invariant in the case he was considering. At one point in his talk, Turing had occasion to write a few decimal numbers on the blackboard and add them up. At first none of us could follow what he was doing until we realized that he was writing the numbers backwards with their least significant digits on the left. There was

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quite a fashion for doing this in Manchester and at the NPL with binary numbers, presumably because that was the way the pulses appeared on a cathode ray tube, but to do it with decimal numbers and without comment was a typical Turing aberration. I really believe that it did not occur to him that a trivial matter like that could possibly affect anybody’s understanding one way or the other. The conference over, we could settle down to work on the library of subroutines and programming research in real earnest. The group of programmers —for they could now be called that—met regularly, and each member undertook the production of one or two subroutines. Wheeler was the life and soul of this particular party. In fact, his exuberance and virtuosity almost wrecked any spirit of co-operation, since, whenever anyone produced a subroutine, he would show how it could be rewritten with a few less instructions and as likely as not so as to do its job better. I needed to take firm measures to curb this excess of youthful enthusiasm. Another research student who made in his own way an effective contribution to the work of the group was Stanley Gill. Before joining the laboratory in October 1949, Gill had spent a year doing national service at the National Physical Laboratory, where he had worked on the ACE project. He was, therefore, somewhat more mature than Wheeler, a difference which his natural seriousness of manner served to accentuate. I began to experiment with methods for numerical quadrature and I made the pleasing discovery that the method of Gauss which, for good reasons, had never been much used by workers with desk ma­ chines was, nevertheless, particularly well suited to a digital computer. This was a prime example of the kind of insight that could come only from actual experience, and which put those who had access to working computers in a different class from those who had not. A similar insight came shortly afterwards regarding the Runge-Kutta method for solving ordinary differential equations. It had not been obvious at first sight that it was possible to write a general library subroutine for numerical quadrature, since the function to be integrated would be unknown when the routine was being written. When I began to tell Hartree of my work on this subject, he remarked that he assumed that it would be necessary for control to be sent back to the main program whenever it was necessary to compute values of the function. I had already realized that it would be better for the integration subroutine to call in a further subroutine—which I called an auxiliary subroutine —for this purpose. Thanks to Wheeler’s pro­ gramming system, which allowed nesting of subroutines and provided a general parameter-passing mechanism, it was entirely straightforward

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to do this. A similar technique could be used for the solution of dif­ ferential equations. It was easy to make advances in those days when the held was so open. It was inconvenient to have to copy the coordinating orders on to the beginning of every program tape. I would have accepted this inconvenience, but Wheeler did not rest happy until he had shown that, by a tour de force of ingenuity, it was possible to write a new set of initial orders that would incorporate the functions of the coordinating orders and still be short enough to be accommodated in the read­ only memory. He put the final touches to these new initial orders during the latter part of August. The Laboratory had dosed for two weeks on 14 August, and Nina and I had gone off to stay for a few days with my mother and father in Worcestershire. When we returned the Laboratory was still officially dosed and it was in an empty building that Wheeler and I had our final consultations. We would have liked to include provision for the reading of decimal numbers from the input tape, but not even Wheeler could put more than a quart into a pint pot. The change to the new initial orders was made on 6 September after the Laboratory had re-opened. In my work on radio wave propagation I had been handicapped by the lack of proper tables of the complex Gamma Function, and I therefore suggested to J. P. Stanley, a Canadian student who was spending a year with us, that he might write a program for computing such a table. This he did and the table (of the reciprocal Gamma Function) was eventually published by the University of Toronto Press. It happened that Stanley’s program was running one day in the middle of August when we had a surprise visit from von Neumann. He was on his way to attend a conference on cosmical aerodynamics in Paris, and had called to see Hartree, who brought him over to the Math­ ematical Laboratory. It was the first time that I had met von Neumann and I was naturally anxious to have his views on computer architecture—logical design, as it was called then. I brought the subject up at lunch, but it was clear that the subject was not one that was uppermost in his thoughts and we did not pursue it. He did, however, remark that he thought that the instruction sets of computers might come to include a square root operation, justifying this opinion by reference to the importance of the square root in Euclidian geometry. My own standpoint was somewhat different, since I had come to regard closed subroutines as providing an extension to the basic instruction set, and did not feel that there was any longer a case for built-in special functions. I had, in fact, been agreeably surprised to find that even the absence of a

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hardware divider was no great inconvenience to the programmer. There were, of course, speed trade-offs to consider, and a hardware divider could certainly be justified on this ground. I mentioned to von Neumann that I would very much like to pay a second visit to the United States. He was good enough to say that if I wrote to him he might be able to help. I did this and he wrote back not only offering me a grant from the Institute for Advanced Study but also saying that he had negotiated for me a matching grant from the Rockefeller Foundation. I was therefore able to plan a trip to North America for the summer of 1950. Many people owe a debt to von Neumann for his kindness and I shall always be grateful to him for making that trip possible. Our interest in programming methodology—as it would now be called —did not prevent us from actively exploring the use of the EDSAC for solving genuine problems. One of the earliest of these was proposed by R. A. Fisher, who was on the Faculty Committee concerned with the affairs of the Mathematical Laboratory and therefore knew about our project. He wrote to me early in 1949 remarking in char­ acteristically barbed fashion that he had understood me to say that our fine new machine was not going to accept only wave mechanics problems to occupy its time, and giving me a differential equation of which he wanted a solution. This was a second order non-linear dif­ ferential equation with two point boundary conditions. Wheeler un­ dertook this job as part of his thesis research; it was quite a difficult nut to crack at that point of time since it involved the programming of an automatic trial and error method for satisfying the boundary conditions at the two ends of the interval. I sent the solution to Fisher at the beginning of April 1950 and he found it waiting for him when he returned slightly later from a trip abroad. I do not think that he had for one moment expected that we would produce a result. He responded in a most appreciative manner and we felt that we had made some progress towards establishing the credibility of electronic computing. Fisher published the table with due acknowledgements later in the year in Biometrics. This was not, in fact, the first publication of results from the EDSAC. It had turned out that my very first substantial program, one for computing values of Airy’s integral by integrating the associated differential equation, could with a trivial modification be made to yield values of an associated function in which R. S. Scorer, then a research student working on meteorological prob­ lems, was interested. Scorer included a table of the function in a note which he sent to the editor of the Quarterly Journal of Mechanics and

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Applied Mathematics at the end of August 1949 and which was pub­ lished early in the following year. By the summer of 1950 we felt that we had made sufficient progress to justify the preparation of a comprehensive report on our methods and experiences. This report was in draft form when I left in August on the trip to Canada and the United States that I shall describe in the next chapter. Mutch put some intensive work into it while I was away, and on my return it was ready for duplicating. We sent copies to everyone that we thought would be interested, both in the United Kingdom and abroad. It had occurred to me that a wider publication of the material would be something to work for and I mentioned this to Professor Z. Kopal of MIT, whom I had come to know in connection with my interest in atmospheric oscillations, when he happened to visit us in October. He at once mentioned a small publishing company—Addison-Wesley Press, Inc. —in Cambridge, Massachusetts, which had published a number of books for authors from MIT. He offered to take back a copy of the report and show it to them. The result was that in early November I had a letter from Addison-Wesley offering to publish the report if it were suitably revised. They must have felt that they were taking a great risk in publishing a book on so obscure a subject as computer programming, and in order to minimize their risk in the event that no-one bought it, they offered the following terms. There were to be no royalties on the first 1,000 copies sold, 20% on the second 1,000 and after that 10% royalties. I am glad to say that the 1,000 mark was passed within fifteen months of the book’s being published in July 1951. It appeared under the names of myself, David Wheeler, and Stanley Gill and differed very little from the report in essentials, although there was some additional expository matter. I like to think that its success contributed in a small way to the growth of Addison-Wesley from being a very small concern to its present large size. In 1982 a reprint was issued as Volume 1 of the Charles Babbage Institute reprint series for the history of computing. The book was published just in time to be used as a text book for a Summer School of two weeks’ duration that we organized in Sep­ tember 1951. At a time when there was very little in print and it was not at all easy to get information about computers, this Summer School and similar ones held in subsequent years —the last one was held in 1958 —served a real purpose. The emphasis was on the EDSAC, but we had guest lecturers from other groups who spoke about the machines with which they were associated. The early courses were strongly oriented towards scientific applications, and included some lectures

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on numerical analysis. The coming of business data processing on computers was envisaged, but had hardly arrived. It would not have been possible at that date to have provided formal lectures on this subject as an alternative to those on numerical analysis; nevertheless, I felt that something should be done for those members of the class whose interests lay in that direction. Accordingly—in 1953, I think it was —I hit on the idea of organising a discussion group with the hope — duly realized —that I would learn as much as the students. It will illustrate the state of thinking on the subject at that time when I say that I stressed in my introductory remarks the fact that, although the use of a computer would imply a high degree of centralization of accounting in a business, this would not necessarily imply centralization of control. There was some fear at first that the data processing manager would come to occupy too powerful a position in a business! Once a library of subroutines and a programming system was in place, use of the EDSAC for serious calculation could start. Naturally, the first users were, with one important addition, members of the Laboratory, staff and students. The addition was Douglas Hartree, whom I have had occasion to mention a number of times. Although Hartree’s affiliation was to another department, he was very close to us at that time. His knowledge of numerical analysis and, more par­ ticularly, his wide experience of computing of the most practical kind, qualified him to play a major role at that critical moment. He had personal qualities of no less value. He was entirely without any sense of his own importance and could work, seemingly on equal terms, with those much younger than himself. He never attempted to lay down the law, and detested people who did. The only time I saw him really angry was once when he had just returned from a visit to the ACE project at the National Physical Laboratory where he had en­ countered such a person. It was, in no small measure, due to Hartree that computer applications in Cambridge got off to such a good start. Research students working with the machine naturally told their friends about it, and it was in this way that the good news spread. Many senior people first heard about the capabilities of the EDSAC from their students. There was a deep-rooted suspicion of new-fangled computing devices that had, I believe, been engendered in part by the over selling of analogue machines that had taken place at an earlier period. I never attempted directly to counter this suspicion when I met it, being quite sure that it would evaporate when knowledge of what the EDSAC could do began to spread. It was helpful in this regard that, so early in its history, the EDSAC had computed a table of primes, a feat that no analogue computer could emulate. I remember

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showing this table to Professor L. J. Mordell, whose subject was the theory of numbers, and seeing his air of scepticism change to one of interest as he realized what it was. As the number of applications from would-be users increased, it became necessary to have some way of processing them. Accordingly I set up a formal committee, with Mutch as secretary, whose role was to interview applicants and, if their proposals were reasonable and within the capability of the EDSAC, advise them on the best way of proceeding. It was really a technical committee but, in order that applicants should treat it with respect, it was called the Priorities Com­ mittee. There was in fact no formal allocation of priorities or computer time. Once a project was approved, the applicant was enrolled by Mutch as an authorized user and he then became entitled to a share, on a level with the other users, of whatever computer resources were available. He was, however, expected to come back to the committee if he wished to use the computer on a project other than the one which had been authorized. The capacity of the EDSAC was strictly limited, and I was anxious that its time should be devoted exclusively to academic research. Projects were chosen for their suitability for running on the EDSAC as much as for their scientific importance. Users had to learn to do their own programming—in assembly language, of course —and, in the state of the art then existing, coaxing results out of the machine was apt to be time-consuming. This meant that, except for a few long­ term visitors to the department, users were all drawn from the Cam­ bridge University community. One long-term visitor was Peter Naur from Copenhagen, who used the EDSAC to compute the orbit of a minor planet, and who has published an account of his impressions in the Scandinavian journal BIT. I used eagerly to look forward to the meetings of the Priorities Committee. Applicants were encouraged to describe the background to their research, as well as the numerical problems they hoped to solve with the aid of the EDSAC. As the circle of users grew, we obtained a fascinating perspective on a wide range of Cambridge research. It was very necessary for the committee to try to understand problems in depth, because so little was generally known at that time about the strengths and weaknesses of digital computers that what seemed to the proposer of a project the obvious way of setting about it was often wide of the mark. Hartree was a member of the committee and, on all questions relating to numerical methods and computational strategy, he was a tower of strength.

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One of the more substantial users from an early date was S. F. Boys, whom I had known around 1937 when he was a research student working under Lennard-Jones on methods for computing the wave functions of chemical molecules. I ran into him again one day after the war when I had lost myself in the corridors of Imperial College, London, and had knocked on the door of a room to seek assistance. In the course of conversation he enquired what I was doing and I told him about the EDSAC, then still incomplete. He listened carefully and then proceeded to give me the reasons why that machine would not be of much help in computing molecular wave functions. After he had returned to Cambridge and had become one of our most prominent users, with a number of students working with him, he was fond of recalling that conversation, and would explain that what he had failed to realize was that digital computers could do Boolean as well as arithmetic operations. At one point, Boys’ work did not appear to be progressing very rapidly and unfortunately he lacked the art of explaining an intricate subject with clarity. One day, after he had mystified us at the Priorities Committee, even Hartree, who had a special interest in the subject, expressed some doubt about supporting the work further. Boys’ real trouble was that he was trying to operate on a scale that was beyond the means available at the time. Later, when machines more powerful than the EDSAC became available, the full extent of his vision became apparent. Some of the functions that he worked with were formed by successive differentiation of a product, and he developed a program for the EDSAC—written, of course, in assembly language—for eval­ uating the terms symbolically. I believe that this may have been the first time a computer was used for algebraic manipulation. He once showed me a notation he had developed to facilitate this work, and I have since regretted that I did not encourage him to publish it. As the number of users grew, it became impossible for the members of the Priorities Committee to follow in detail everything that was being done on the machine. The Mathematical Laboratory was no longer the only place where expertise in programming was to be found. Other departments in the University began to acquire experience and to recruit programmers to their staffs. What had begun as a band of enthusiasts sharing a new toy, took on the dimensions of an em­ bryonic computing service. From the beginning Mutch acted as man­ ager of this service. Here, as elsewhere, previous experience was lacking and new ground had to be broken. The efficient but unobtrusive administrative support that Mutch provided, along with good docu­ mentation of the facilities available, enabled informal collaboration to

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flourish between those inside the laboratory and those outside it. Many new computer applications were pioneered in this way and a steady stream of papers came out reporting on research in which the EDSAC had played a large or small part. A factor by no means without its importance was that there was no financial accounting for computer time and hence no reason to favour the rich over the brainy. In 1961 the University gave Mutch the official title of Superintendent of Com­ puting Services. It was a great shock to all of us in the Laboratory and to his many friends and admirers elsewhere when he died suddenly of heart failure in 1969 at the early age of 47.

15 Germany revisited

Sometime towards the end of 1947, or the beginning of 1948,1 began to receive telephone calls from a Commander Studdert at Minden in northern Germany where the Royal Navy had a headquarters. Com­ mander Studdert had heard that I knew about differential analysers, and it was on this subject that he wanted my advice. He explained that a group led by a German engineer was designing a machine with support from the Navy. I never enquired about the origin of the project, nor how the support had come to be given, but I assume that it was part of a larger scheme to aid the re-establishment of the German economy. My visit to Germany in 1945 had made a deep impression on me, and when Commander Studdert suggested that I might go again I readily agreed. And so it happened that on Saturday 13 March 1948 I called at the Admiralty in order to complete certain formalities before taking the overnight boat to the Hook of Holland. One of the things I did at the Admiralty was to visit an official with the delightful name of “Paymaster of Contingencies” in order to get some of the special money, known as scrip, used by the occupation forces in Germany. This had no value outside Germany, and had been introduced to close a serious gap in the exchange control system that had been detected some time earlier. On the Harwich-Hook route there were military trains and a military boat operating in parallel with the ordinary civilian services. When we arrived at Harwich, I found that I was being treated as a VIP and I was met by a Chief Petty Officer who saw me aboard. It was a good thing that he did, since my documentation was defective, and he had to do some hard talking to get me through. I had been given the equivalent rank of Commander for the purpose of this trip, which was an improvement on Squadron-Leader which I had had last time. Nearly ten years later, when I thumbed my way to Australia with

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RAF Transport Command, I enjoyed the equivalent rank of Group Captain. So one makes progress. I arrived in Minden in the British zone of occupation on Sunday evening, and was hospitably received by Commander Studdert. The group working on the differential analyser had its headquarters in Gottingen, and was led by Dr Buchner. I had said that I would like to take advantage of my presence in Germany to make one or two contacts unconnected with the main object of my visit, and Commander Studdert very kindly agreed that the car that was to take me to Gottingen should remain at my disposal for the rest of the week. Lieutenant Lawlor was to come with me, and a very efficient escort he proved to be. Direct military government of Germany had ceased, and the British zone was being run by a civilian Control Commission, responsible to the Commander-in-Chief. A similar arrangement existed in the U.S. zone. The British and Americans worked closely together and the two zones were sometimes referred to as Bizonia. The Russians, on the other hand, persisted in the policy of separation that they had started in 1945. Troops and civilian personnel in the British zone were still being supplied with the necessities of life from the United Kingdom, and still enjoyed the privilege of duty-free drinks. The full impact of this hit me when I was staying in the T Force transit hotel in Gottingen and, after having had a few large drinks at nominal prices, I realised I would have to be careful. My week’s work began with a long talk with Dr Buchner, the leader of the team working on the differential analyser, in Commander Studdert’s office in Minden. This was continued the next day in Gottingen. The design had already proceeded some way. In one important respect it was influenced by a machine built in Oslo before the war. In this machine the integrators were not mounted with their axes vertical, as they were in Bush’s original design, but horizontal. This had the advantage of saving space, but it introduced a number of mechanical problems, and I was not too happy about it. The main challenge that faced the designer of a mechanical differential analyser was that, even if every precaution were taken, the accuracy of the integrators would fall far short of what could be desired from the point of view of the user. The design of a better than ordinary mechanical differential analyser really required someone who could combine the point of view of an instrument designer with that of a mechanical engineer. Bush realised this, but not all of those who followed him did. I had been somewhat disappointed with the accuracy of the differential analyser we had in Cambridge, and I had had to make certain mod-

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ideations in order to reduce backlash at a critical point. I did my best to bring these points home to Dr Buchner and his team, and hope that my visit may have been of some value. The machine was eventually completed and installed at the National Physical Laboratory, where it ran for some years. While in Gottingen I was able to meet Professor Julius Bartels who was one of the leading figures in the world of geomagnetism. Bartels was a great friend of Chapman’s and together they had produced a large two-volume work on that subject. The manuscript was fortunately complete before the war, and publication took place in England in 1940; by that time Chapman was working at the War Office and Bartels was an enemy alien! Bartels had been summoned to meet me at the Control Commission Research Office and I do not think that he knew in advance what it was all about. Perhaps he thought that he was in for trouble of some kind. However, when I explained what my interests were and presented him with a reprint of the paper that I had written with Weekes, he was delighted to meet someone who was interested in the motion of the atmosphere, and in particular in the effect of the moon on it. He greeted me as a fellow “lunatic” and we had an animated discussion. Afterwards he took me along to his Institute and showed me the seismological instruments. He lived alongside the Institute and his wife insisted that I should have a cup of tea. This was a commodity that was quite unobtainable in Germany at that time, but Bartels had recently had the opportunity of visiting Chapman at Oxford and he had brought some back with him. For­ tunately, I was able to respond by giving them some cigarettes, which had come to have almost the status of currency in the Germany of that period. I could not stay very long since Lieutenant Lawlor and I had planned to go that night to Winterburg, a recreational centre in the mountains run for the benefit of allied personnel and more or less on our way to Frankfurt, which was our next port of call. However, I made an appointment to see Bartels again later in the week. It snowed next morning at Winterberg, and we admired the rather fine scenic effects as we drove to Hochst near Frankfurt, where we made our number with the local military authorities. We were now in the American zone and in territory that I had known before. I left Lieutenant Lawlor to transact some business in Frankfurt and went off with the driver to look up Professor Walther at the Technical University in Darmstadt. I had met Walther briefly when he had visited England under Comrie’s auspices. The Technical University had been badly bombed, and Walther’s Institute was housed in a few rooms that had somehow been patched up. All around was devastation. It

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was typical of Walther that he should have managed to get things going at all under those unfavourable conditions. Walther was not at the Institute when I arrived, but I eventually tracked him down at his home, and we spent a pleasant afternoon in discussion. I cannot re­ member what topics we covered, but I do not think that much was said about the newer developments in electronic computing. He did not mention the work of Konrad Zuse and indeed it was not until much later that I first heard Zuse’s name mentioned. I arranged to go back the following morning and, if Lieutenant Lawlor agreed, to convey Frau Walther to Gottingen where she wished to visit her son, who was reading medicine there. When I arrived back in Hochst I found that Lawlor had arranged for us to stay at a newly-opened luxury hotel in Bad Homburg. This was intended to provide accommodation for the business men who were now visiting Germany in increasing numbers in order to re-open trade relations. I suppose that to most of the people who stayed there it was just like any other first class hotel, and that they did not realise what a contrast it afforded to the general poverty in which the Germans were living. The same contrast, of course, existed in any of the messes or hotels provided for the occupying powers, but somehow I felt it more acutely—and was slightly uncomfortable as a result—in the highly luxurious civilian atmosphere of the hotel at Bad Homburg. I tried hard to get a view of how the Germans were really living, but found it very hard to get accurate information. Much of what one was told, both by Germans and by English people, did not seem to bear examination when confronted with the facts. One girl told me that they had had no new clothes since 1943, but her appearance belied this. Perhaps she was discounting the black market which in some places, such as Frankfurt, was conducted openly and in other places less openly. Frau Walther told me that only women’s clothes were available on the black market, and that she had had some difficulty in getting her youngest son his first pair of long trousers. People in the country were relatively well off, and those in the large towns least so; it helped if they had connections in the country or access to manu­ factured goods that they could barter. The shops had very litde for sale, but many of them carried notices of offers to exchange specific articles, for example, a sewing machine for a radio. In spite of stories about civilian rations being below those of the prison camps, the Germans I came into contact with showed no sign of undernourishment, although I can believe that they were sometimes hungry; also they were very far from being in rags. The Walthers seemed surprised to hear that in England, if one got a man to do a job in a house in his

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spare time, for example repair a door, he would accept money and not demand food. Bartels told me that civilian rations were coming through all right, but that there had been no allocation of meat for some weeks. I was anxious to see how much Frankfurt had changed since I last saw it two and a half years ago, and we had driven that way to Darmstadt on Thursday instead of going by the autobahn. Men were hard at work clearing away debris, although they had made little impression and, while the town was more of a going concern, it appeared as ruinous as ever. When I saw Bartels again on my way back through Gottingen he told me that Dieminger was at Lindau, near Northeim, about twelve miles to the north. Accordingly I called to see him on the way to Minden. He had apparendy had difficulties in Ried in Austria where the people were not too friendly, and it was largely through the efforts of W. R. Piggott that he had been resettled with his Institute at Lindau. He had a workshop and an emergency generator plant, and had an ionospheric recorder in operation. The Fraunhofer Institute at Lindau developed into an important organisation and Dieminger continued to lead it until his retirement in 1975. Back in Minden there were a few things to clear up and I had a final chat with Commander Studdert. On my last evening the whole mess went to dine at the 21 club at Bad Oyenhausen, the headquarters of the British Army of the Rhine, and they took me with them. Next morning I caught the 9.05 train to the Hook of Holland and thence home. It had been dark when I came this way a week before and I was surprised at the amount of air-raid damage visible from the railway, mostly of course in the towns, the countryside being largely undamaged. Building work was more in evidence in the country than in the towns. The contrast when we crossed the frontier into Holland was most marked; here everything seemed neat and tidy. We stopped at a number of stations and people came along the platform selling things, the currency being cigarettes. For example, just inside the Dutch frontier one could get an English paper for two cigarettes and at Utrecht one could buy a fair-sized box of chocolates for 40 cigarettes. In neither case did the trade appear to be at all brisk. On the boat I was shown into a cabin with some other civilians. Later I was called on the loud-speakers and met by an apologetic OC Troops who said that he had reserved a special cabin for me with a Naval Commander. Before turning in we had a short chat about conditions in Germany. He took the view that the German officials

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who were working with the Allies were not quite tip-top and that it might even be necessary to bring back some of the Nazi experts. I had, in fact, heard much talk of this kind. Many allied officials were strongly critical of the Germans, and Lawlor had warned me not to believe everything I was told. Certainly many Germans of the better kind were understandably holding back from participation in public affairs so as not to incur the stigma of collaboration with the occupying powers. At the heart of the matter was the existence of the black market and the corruption that it implied. Until this had been dealt with, the re-establishment of normal standards of governmental and economic probity could not take place. All was to be changed overnight with the currency reform of June 1948. This drastic measure had the effect of reducing severely the amount of money in circulation and so forcing people to live on their incomes; bank balances were reduced by a factor of ten, while incomes and prices were kept as they were. Goods then appeared in the shops once more, and the West German economy was firmly set on the path to recovery.

16 Computer progress in the United States

At the time of my first visit to the United States the initial phase of the development of the modem digital computer may be said to have been over. The Automatic Sequence Controlled Calculator at Harvard University had shown that it was possible to build a fully automatic digital computer, and had demonstrated some of the uses to which such a device might be put. The ENIAC had shown that vacuum tubes could be used instead of electro-mechanical elements and that, in spite of the very large number of vacuum tubes required, the overall re­ liability would be adequate for the purpose. Eckert, Mauchly, von Neumann, and others engaged on the ENIAC project had put their heads together and evolved the set of ideas that von Neumann wrote up in the document entitled “Draft report on the EDVAC”. By the time of the Moore School course these ideas were complete, and that unique and fruitful interlude when contributions to computer design could be made by both mathematicians and engineers was over. The initiative now lay with the engineers exclusively. Their task was to build a working computer that would embody the ideas that had been jointly evolved. The task facing a group setting out to build an electronic computer was more difficult and challenging than might appear to a non-engineer. It was easy enough for an engineer to explain to a mathematician how vacuum tubes could be used to make digital circuits; to do it in practice was another matter. Vacuum tubes did not lend themselves naturally to this purpose, since they were essentially analogue devices. In fact the whole problem of digital engineering lies in the fact that there are in nature no such things as true digital devices. The engineer’s task is to take more or less refractory analogue devices and persuade them to behave in a digital manner. Learning how to do this with vacuum tubes was the first task to which the various groups had to

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address themselves. They arrived at surprisingly different solutions, since it turned out that there was not one way, but a number of ways in which it could be done. Some of the differences will emerge in the sequel. There was a natural tendency for each group to think that the design principles at which it had arrived were the only true ones. In fact, it turned out that quite different approaches were equally suc­ cessful; the important things were consistency and sound engineering. Some years later, when the initial excitement had died down, Sam N. Alexander, who had been with me on the Moore School course, remarked that he, for one, no longer thought that a particular phi­ losophy of design was the one and only. This became very obvious when transistors arrived and people began to speak of “families of logic” *. There was, of course, much more to the design of a working com­ puter than the design of the switching circuits; for example, physical layout, cooling, power supplies, and so on all had to be considered.The connection of mechanical input and output devices to an electronic machine also presented a number of unexpected problems. In the early days the mechanical input and output devices available were slow and unreliable, and this added in no small measure to the worries of the designer. The history of the development of mechanical computer peripherals is a success story in itself, and has had repercussions outside the computer held proper. While the EDSAC was being built and the foundations of a pro­ gramming system were being laid, a fair amount of news had reached me of the corresponding projects that were in progress in the United States, but I was without first-hand knowledge. The prospect of another trip to that country was, therefore, an exciting one. On 8 July 1950, I took the boat train from London to Liverpool to embark on the RMS Newfoundland, due to sail that day for New York, calling at St John’s and Halifax. My original intention had been to go all the way, but a little time before sailing I received an invitation from Kelly Gotlieb to visit Toronto and give a lecture at the University. Accordingly I arranged to leave the ship at Halifax, where I was assured a ticket for the long train journey to Toronto would be waiting for me. !f The origin of the colloquial term “logic” to mean a digital circuit or a portion of a digital circuit is interesting. Claude Shannon had used the notation of formal logic—in particular Boolean algebra—for analysing the behaviour of relay circuits and this was taken over to describe electronic circuits also. It gave rise to the term “logical design” for the process of designing such circuits and hence the term “logic” in the sense indicated above.

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The RMS Newfoundland was a small ocean liner of less than 10,000 tons. I had a comfortable cabin to myself and I sat at the Chief Engineer’s table in the dining saloon. Life aboard was very enjoyable and the time passed quickly. We entered St John’s harbour early in the morning of Friday 14 July, and after the usual formalities we were free to go ashore and look around. Some cargo was being taken aboard and we were not due to sail until the following afternoon. The steamship line had arranged a motorcoach tour for us, and we were shown the local sights. Most interesting from my point of view was Telegraph Hill where Marconi conducted his experiments in transatlantic radio communication in December 1901. We docked at Halifax on the morning of Monday 17 July. I was more than a little perturbed when the mail came aboard to find that there was nothing for me. However, before long a representative of the Canadian National Railways turned up with a prepaid ticket to Montreal, together with 25 dollars in cash. The train was not due to leave until about 4 o’clock, so I sent my bags to the station and took a stroll round Halifax, returning to the ship for a final luncheon aboard. The train jogged its slow 850 miles from Halifax to Montreal through the forests of the Maritime Provinces, and then right through the heart of French Canada. I saw Quebec across the St Lawrence, and a fine city it looked. The train arrived in Montreal just after 8 p.m. on 18 July and while I was waiting for my luggage to be brought up I was called on the loud speaker and told that a berth on the 11.59 train to Toronto was being held for me. I took a brief stroll along St Catherine’s Street and wished that I could have had more time to explore the city. Travel in those days was a long-drawn-out, even leisurely, proceeding, at the end of which one was plunged suddenly into activity. At the University of Toronto everyone wanted to talk about computers, and I gave, for the first time, a lecture I had prepared about the EDSAC and the programming system we had evolved for it. I included, of course, a description of Wheeler’s initial orders. The audience was well informed about what was going on, and they had had a number of lectures from people associated with various computer projects. However, this was the first time they had heard anyone who had had actual experience of a working stored program computer. Afterwards, Kelly Gotlieb expressed this by saying that mine was the “second lecture of the course”. I also found waiting for me an unexpected message from Andrew Thompson, Head of the Meteorological Office in Toronto, whom I had met at Oslo and who shared my interest in atmospheric

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tides. He entertained me to dinner on the Thursday evening and on the Friday morning I gave a lecture at his Institute. Since von Neumann had organized the finance for my trip, I naturally proposed to base myself on the Institute for Advanced Study at Prince­ ton and I travelled there overnight on 23 July. The Institute was situated a mile or two outside Princeton and in the grounds there were a number of small houses in which members of the Institute staff could live. I was given the temporary use of one of these, its regular occupants being on leave. I liked being able to cook my own breakfast and other meals when necessary. I was glad to meet Goldstine again. He introduced me to Julian Bigelow who was in charge of the engineering design and construction of the computer. Naturally, I had a good deal in common with Julian, and during the time that I was there I got to know him very well. Julian and his wife, Mary, lived in a similar house to mine, and, so that I should not be entirely without transport, they kindly lent me a bicycle. At the Institute I shared an office with Charles V. L. Smith, who worked for Mina Rees at the Office of Naval Research in Wash­ ington, which was funding the project. Charlie was spending a few weeks at Princeton in order to monitor the progress that was being made. Somewhat earlier Goldstine, von Neumann, and Arthur Burks had written a series of what were described as preliminary reports on the planning of programs for an electronic computer. These were privately circulated instead of being published, and I do not think I had seen them before; if I had, they had made no impression on me. I spent some time studying these reports and was particularly interested to compare their method of relocating subroutines with the one that Wheeler had implemented. A feature of the reports was a formal method of drawing and annotating flow diagrams; I now realize that to attach importance to formalism was typical of the von Neumann approach. The logical design of the computer—what we would now call its architecture —followed the outline given to me by Goldstine four years earlier in Philadelphia. The implementation was entirely due to Bigelow and he had adopted an interesting and highly original form of con­ struction for the arithmetic unit. As far as the distribution of power was concerned this was, in a sense, a forerunner of the modem multilayer platter. The platter was, however, folded in such a way that low capacity air-spaced wiring could be used to convey the pulses. This attention to stray capacities gave the machine a high speed for the period, although some of this was lost because Bigelow had decided

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to use an analogue adder. In some of the copies of the machine that came to be built later, a logical adder was substituted. The machine was DC coupled and could, for testing purposes, be run at an arbitrarily low pulse repetition rate. I was rather envious of this feature. Bigelow was very conscious of the danger of pattern sensitivity being introduced by the presence of capacity in the circuits, and would not even admit the introduction of “speed-up” capacitors in the flip-flops. Bigelow had had some trouble in getting the analogue adder to work with adequate margins. He had discovered the im­ portance with this kind of circuit of doing a carefully toleranced design on paper in advance of construction. I well understood what he was talking about, since I had had a similar experience with the (much simpler) analogue circuit for inverting the least significant digit in the EDSAC input system. This had worked very erratically, until I had sat down and worked out a properly toleranced design. The arithmetic unit—a term then used for the processor without the memory—was in a more or less working condition, but the project as a whole had been much held up by the failure of the Selectron memory tubes to materialize, Rajchman’s optimism in 1946 having proved to be misplaced. It had become clear that some other memory must be used instead, and fortunately the Williams tube memory had come along just in time. However, the use of this form of memory for a parallel machine implied major development work, since Williams’ original serial design could not be adopted as it stood. This development work was very exacting, since it involved the design of highly accurate and stable analogue deflection circuits for both the x and y coordinates. Moreover the very low signal levels at which the Williams tube operated made it imperadve to pay close attention to screening and the avoidance of unwanted coupling. In spite of these difficulties, Bigelow had made very good progress and had pushed ahead with the mechanical con­ struction to a point at which it was virtually complete. He was, however, not entirely satisfied with the performance and there were a number of important circuit details still to be finalized. In the case of the EDSAC quite a lot of effort had gone into the design of the main control unit and the arithmetic control unit. By contrast, Bigelow had not built any corresponding units, nor did he appear to have made detailed plans. This puzzled Charlie Smith and myself. When tackled, Bigelow merely said that the matter would present no difficulty and that he would deal with it at the appropriate time. What I did not then realize is how much simpler the control circuits are in a parallel asynchronous machine than in a serial syn­ chronous one. Apart from that, however, there was another feature

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of the Institute machine that led to simplicity in the control circuits. This was that the operation code of an instruction contained as many as ten bits, and these bits were allocated in such a way that decoding was largely unnecessary. One day, while I was talking to Goldstine about the methods of programming that we were cultivating in Cambridge and about our experience with them, von Neumann looked into the office. I explained to him Wheeler’s method of entering and returning from a closed subroutine. Sharp and quick as always, he appreciated the elegance of the method and I believe referred to it in a lecture that he gave shordy afterwards. However, although von Neumann and Goldstine had written with Burks the reports on programming methodology that I referred to above, they did not at that time give the impression of being drawn to its intellectual and organizational challenges. They tended to see a computer as being used for two or three large problems, and it was the mathematical planning of the program that was of interest, and not the mere detail of coding, which they felt would be done by a few experts anyway. My own experience had already made me begin to see a computer as providing a service for many people and running large numbers of little programs as well as some big ones. It had become obvious that if programming were really to be left to a few experts it would become a bottle-neck and that the only way out was for users to do their own programming. To this end, it was a matter of urgency to develop streamlined methods of pro­ gramming and of debugging. While at Princeton, I began to plan the rest of my trip. Of high priority was a visit to the Eckert-Mauchly Corporation in Philadelphia. Next I wanted to go to Washington to visit the Bureau of Standards and also the U.S. Army Proving Ground at Aberdeen and the cor­ responding Naval Establishment at Dahlgren. Both these places were within a car ride of Washington. Goldstine was very helpful in arranging for me to receive the necessary permission to make these visits. I planned to spend some time in the Boston area at the end of the trip in order to visit Harvard and also MIT, where there was an important project in progress. The Princeton machine and the EDSAC could not have been more different in their conception or in their detailed design. Nevertheless, Bigelow and I had been facing what was fundamentally the same set of problems and it had been a broadening experience to compare notes with him. It was with a feeling of satisfaction, therefore, that I left Princeton at the end of July to stay for the weekend with John Mauchly on a property that he had recently acquired on the outskirts

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of Philadelphia, and to take a brief look at the progress being made with the UNIVAC. John met me at the station at Philadelphia and took me to the premises of the Eckert-Mauchly Corporation for a quick tour of in­ spection before going to his home. He and Eckert had realized, quite righdy, that in designing a commercial computer they could not afford to cut comers in the way that one could in an experimental project, and they were leaving nothing to chance. However, this meant that the project was both costing more and taking longer than they had originally estimated. Shortly before my visit Eckert and Mauchly had suffered a great blow. Their sponsor, with whom they had only been associated for a short time and who was proving very understanding and patient, was killed in a tragic air accident. In consequence of this the Eckert-Mauchly Corporation had been absorbed into RemingtonRand. The name of the Corporation survived for a time as the name of a division of Remington-Rand, but in due course it disappeared; the name “UNIVAC”, which they gave the computer they were de­ signing, survived until recently —the only one of the early computer names to do so—but, unhappily, it too has now disappeared. John Mauchly had married again and I was warmly welcomed by Kay Mauchly when I arrived at her house. Kay had worked as a programmer on the ENIAC and I had got to know her quite well on my previous visit. The children seemed very happy under Kay’s care and she now had two, I think, of her own. On the Monday morning John took me back to his plant. A feature of the UNIVAC development was the use made of magnetic tape and the emphasis placed on obtaining high performance from it. The plastic magnetic tape available commercially at that period had been developed for audio recording and, while perfectly adequate for that purpose, was too full of defects to be satisfactory for use with a com­ puter. Instead of trying to secure plastic tape of adequate quality, Eckert had chosen to go to tape made of a non-magnetic metallic alloy plated with a magnetic coating. Even so there were defects whose effect it was necessary to neutralize, and a system of marking these with a hole punched in the tape and sensed optically had been de­ veloped. The tape drives—called Uniservos—were highly developed and were capable of reading tape at high speed in either direction. A device, known as a Unityper, whereby an operator could record information on the tape at slow speed —and at a rather low packing density —had also been developed. A tape written on a Unityper could subsequently be mounted on a Uniservo and read into the computer at high speed. My impression is that this device and similar

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devices developed elsewhere were not very successful; certainly, it was many years before large computers were able to dispense with punched cards for input purposes. I remember Arthur Samuel remarking to me a year or two later, in connection with the 701, that IBM had made a serious attempt to get away from punched cards, but had been led back to them for their convenience and efficiency compared with other media available at the time. I have no clear recollection of what else I saw in the hardware line, but I do remember some stimulating discussions with the group, led by Grace Hopper, who were concerned with programming, in the course of which I gave a short talk about our experiences in Cambridge. I found that they had a full appreciation of the importance of pro­ gramming and of the need to develop organized and disciplined meth­ ods. I felt that I was among people who looked at things in the same way that I did myself. I have remarked above that Eckert left nothing to chance in the design of the UNIVAC. He would never be satisfied with anything less than the best. I had a good illustration of this a few years later when I was again visiting Philadelphia to attend a conference. One evening I accepted, along with other participants, an invitation to visit the Eckert-Mauchly plant where we were shown several UNIVACs in various stages of final assembly and checking out. Computers were then still rare objects, and it was an impressive sight to see a number of them in one room. Eckert spotted me in the party, drew me aside and took me behind the scenes to see some of the details. We fell to talking about the design of mercury tanks. The UNIVAC, like the EDSAC, used both long tanks, capable of holding many hundreds of digits, and short tanks, capable of holding only a few digits. The former were used in the main memory and the latter for various purposes in the arithmetic unit. Short tanks were significantly more difficult to design than long tanks. This was because the pulses were partially reflected from the quartz crystals at the ends of the tanks and could make a number of passages from one end of the tank to the other before dying out. This did not happen in the case of the long tanks because the attenuation suffered by a pulse in travelling the length of the tank was too great. The way that we dealt with the problem in Cambridge was to have an adjustable screw projecting into the mercury so as partially to obstruct the passage of the pulses and thus increase the attenuation. This scheme worked, but only just. The setting of the screw was very critical and I never felt happy about it. It would certainly not have satisfied Eckert. He had attacked the prob­ lem at its source by reducing the amount of reflection from the crystal.

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This he had done by backing the crystal (on the side opposite to the mercury) with a slug made from a special lead alloy which presented the same characteristic impedance to ultrasonic pulses as did mercury. Since the characteristic impedance of quartz was also close to that of mercury, the effect was that very little of the ultrasonic energy incident on the crystal was reflected, nearly all of it passing through into the lead to be dissipated by absorption or scattering. Monday afternoon I spent at the Moore School. When I arrived the computer group were in session under Morris Rubinoff, and I was invited to join in their discussions. The original team had been pretty well broken up when Eckert and Mauchly left, and the EDVAC project had faced great difficulties. Nevertheless, the machine had been com­ pleted and moved to Aberdeen in Maryland, where the process of making it work was proving to be a slow one. My next port of call was New York City, where I went to see the Selective Sequence Electronic Calculator that IBM had installed at their World Headquarters on Madison Avenue. This was a strange machine containing vacuum tubes, a bank of relay memory, and a sequencing system owing something to the Harvard Mark I and something to later ideas. It was a pity that the effort put into it had not been put into a development that was more in the mainstream. Vacuum tubes and relays do not mix well together, and it is not surprising that the IBM machine was rather temperamental. Nevertheless, it could, with the aid of duplicate programming, be made to work, and it was manfully chugging away integrating some equations in celestial mechanics. At that time any working computer was of great interest and I went in some detail into the coding methods being used. I spent the rest of my two days in New York sightseeing and going to the theatre, and on the Thursday I took the train to Washington where I was to visit the Bureau of Standards. The Bureau had made a decisive intervention in the computer field. Starting relatively late, they had established two projects, one in Washington for the con­ struction of the SEAC (Standards Eastern Automatic Computer) and one on the West Coast for the construction of the SWAC (Standards Western Automatic Computer). The latter as I have already mentioned was being built by my old friend Harry Huskey. The SWAC was due to be inaugurated in Los Angeles on 17 August, and the Bureau of Standards with great generosity invited me to go there as their guest. The SEAC had been in operation for some time. It was well conceived and was the best engineered of all the early machines. The person responsible for the SEAC was Sam Alexander. Like the EDSAC, it was a serial machine with a mercury tank memory. Again like the EDSAC,

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the switching was done by diodes, vacuum tubes being used only for amplification. Alexander and his team were, however, ahead of us in using germanium diodes instead of thermionic diodes, and well ahead of their time in making use of plug-in packages. Each package contained one vacuum tube and a number of diodes; it introduced a delay of exactly one clock interval. The output of each package was synchronized and standardized with the aid of centrally generated clock pulses. I regarded Sam Alexander as one of the soundest computer engineers of the time and I always looked forward to meeting him. The SEAC was very successful and as time went on an experimental Williams tube memory was added to it, together with an auxiliary memory based on magnetic tape. Another feature added was a system of input and output based on magnetic wire. This used cassettes from a dictating machine, and did away with the use of punched paper tape or punched cards. An interesting development that came out of Alexander’s lab­ oratory was a diode-capacitor memory in which the information was held in capacitors and periodically refreshed. If for any reason the core memory had proved unsuccessful, this device would have had a bright future. The refreshing principle reappeared later in dynamic semiconductor memory chips. The Bureau later built a successor ma­ chine to the SEAC, known as the DYSEAC, which was much ahead of its time in providing for external interrupts. This should have led to important advances but, unfortunately, the Bureau had to give the machine to the sponsor who had met the cost of its development and nothing more was heard of it. There were many people at the Bureau in Washington who had had a good deal of practical experience of programming. Rather to my surprise I found that they did not, like myself, take it as obvious that a programming system should be based on a library of subroutines, and in particular did not share my view as to the merits of closed subroutines. Instead they preferred to do their coding directly from a detailed flow diagram. A lot of time on the SEAC was devoted to linear programming, a subject then relatively new and attracting a good deal of attention in the United States. The head of applied mathematics —including programming activ­ ities—in the Bureau was J. H. Curtis, and under him F. L. Alt was in charge of the programming for the SEAC. I also met John Todd, who had been with the Admiralty Computing Service in England during the war and his wife Olga Tausky, also a mathematician at the Bureau. John drove me to the US Army proving ground at Aberdeen, Maryland, where I renewed my acquaintance with the ENIAC, which had been moved there from Philadelphia. I was also able to see their differential

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analyser and a large Bell relay machine (Model V), one of two such machines constructed. I talked at some length to R. M. Clipinger on mathematical and programming topics. Shortly afterwards I paid a visit to the corresponding Navy estab­ lishment at Dahlgren in Virginia where the Harvard Mark II, a relay computer that I had seen under construction at Harvard on the occasion of my earlier visit, was working. Another machine built in Aiken’s laboratory, the Harvard Mark III, was in process of being commissioned. This was a rather low performance electronic machine, with separate magnetic drums for storing instructions and numbers. One of the programmers made a remark in connection with this machine that set me thinking. It was to the effect that they would find it hard to get used to a machine that did not have a floating point arithmetic unit. Both the Harvard Mark II and the Bell Model V relay computers had this feature, but the early electronic machines did not, the reason being that no electronic designer could then face the additional complexity that floating point operation would entail. It was some years before engineers felt up to the task of designing floating point arithmetic units for electronic machines, and by then a rather odd theory had grown up on the part of some users to the effect that a floating point arithmetic unit would be a stumbling block rather than a help, because of the cancellation of significant digits that would take place in certain circumstances. I was never taken in by this argument and, indeed, it dissolved overnight when floating point arithmetic units began to be made available in electronic computers. I learnt while in Washington that it was proposed to hold a meeting of the Association for Computing Machinery there in early September. I had intended to leave for home at about that time, but I was able to change my reservation for one on the Queen Mary, which was due to sail from New York on 14 September. On 11 August I left Washington by air with the object of visiting the University of Illinois at Urbana and then going on to Los Angeles for the inauguration of the SWAC. The weekend I spent in Chicago where I paid my first visit to the Art Institute. My interest in painting had been aroused some time earlier when Nina and I paid a chance visit to the Fitzwilliam Museum in the company of Pat Newton (later Pat Machin) with whom Nina had formed a close friendship when they served together in the Army during the war. Pat drew my at­ tention—shyly, as if uncertain of my response —to the magnificent painting of a man in military dress that had formed part of the founder’s bequest and was then attributed to Rembrandt. She could have chosen no painting better calculated to appeal to untutored eyes. I went back

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to it soon afterwards. In Chicago I came under the spell of Rembrandt’s ‘Girl in a Doorway’ painted in 1645, a picture that continued to haunt me for a long time afterwards. Later, when Nina and I went to visit her brother, who was living in The Hague, I was able to study the Rembrandt paintings in the Mauritshuis. It was only gradually that my interest spread to other painters as I acquired an understanding of their work. At about that time Niklaus Pevsner became Slade Pro­ fessor of Fine Art in Cambridge and held the chair for two tenures of three years each. I learnt much from his lectures, particularly from those on architecture which one felt was where his real love lay. I got to know Pevsner personally, since he held a Fellowship at St John’s during the time that he was Slade Professor. As it happened, I was elected to a Fellowship at the same time and we were admitted on the same day. The visit to Urbana was brief, but very interesting. The University of Illinois had set out to build a copy of the Princeton machine, and I spent a good deal of my time with R. D. Meagher who was in change of the work. Meagher had followed Bigelow’s design very closely, and the whole of the arithmetic unit was complete. However, work was now held up since Bigelow was not prepared to release the details of his design for the Williams tube memory until he was entirely satisfied with it. Meagher was under some pressure to go ahead independently, but was adopting a very cautious attitude. I felt that he was quite capable of completing the design himself, and in the end he did so very successfully. Quite a number of copies, or near copies, were made of the Princeton machine, and some of these were copies of the Illinois variant. The one I saw being built went to Aberdeen, where it was known as the ORDVAC. The copy of it that shordy afterwards went into service at Urbana was known as the ILLIAC. A third copy, built at the University of Sydney in Australia, where my former student John Bennett was now professor, was known as the SILLIAC. I saw this machine in Sydney in 1957. A pleasing feature was that it was placed across the comer of the room, just like the ILLIAC in Urbana. The group at the University of Illinois bore a closer resemblance to our Cambridge group than any of the others that I had encountered, or was to encounter, in the United States. It was partly this that led me shortly afterwards, when David Wheeler had taken his Ph.D., to write to Professor J. P. Nash, Head of the Laboratory, to enquire whether they could find a temporary post for him. Nash replied in a positive sense, and Wheeler spent two years at the University of Illinois as a visiting assistant professor. He was succeeded in that capacity by

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S. Gill and A. S. Douglas, who each spent one year at Urbana. Thus, quite a close connection was established between the two laboratories. I paid another brief visit to Urbana in 1956. Nash was then on the point of leaving to take up a post in industry. He and I had met on a few occasions only but, as he remarked, our relationship, conducted through the intermediary of a series of visitors from Cambridge to Urbana, had been quite a close one. Wheeler arrived at Urbana in time to influence the design of the ILLIAC programming system which, in consequence, bore a close family resemblance to that of the EDSAC. The Williams tube memory, although an undoubted success, needed careful nursing. One of its foibles was that a particular digit could be corrupted by repeated reading of adjacent digits. As part of the regular maintenance procedure, it was necessary to measure what was known as the “read around ratio”. Wheeler became quite famous for his “leapfrog test” which would test a section of memory and then copy itself ahead into the tested section ready to test another section. Many of the problems with Williams tube memories arose from the fact that it was necessary to use commercially available cathode ray tubes which tended to have minute, but extremely troublesome, imperfections in their screens. The computer industry was then too young to be able to demand special quality tubes from the manufacturers. Before the matter could be thoroughly sorted out, the Williams tube memory had been rendered obsolete by the coming of the core memory. If this had not happened, we would undoubtedly have seen major de­ velopments in cathode ray tube memories. At the time of my visit in 1950, L. N. Ridenour was Dean of the Faculty under which the Digital Computer Laboratory came, and the Laboratory owed much to his support. He took Meagher and myself to dinner at the Urbana-Lincoln Hotel the night before I was due to leave. It was very hot and humid, and I remember what a relief it was to go into an air conditioned room. Except for hotels, bars, and the occasional computer room, air conditioning was still uncommon. Ridenour himself was going to Los Angeles the next day on the same flight as myself, and he offered me a lift to the Chicago airport in a light aircraft operated by the University of Illinois. Thus I had the experience of flying to Chicago in a single-engined aircraft, sitting by the pilot, and then getting into a huge commercial aircraft to fly to Los Angeles. The word huge is to be interpreted according to the standards of the times; it was, in fact, a DC6 and carried about 50 passengers, the flight time to Los Angeles being 7 hours. Aircraft did

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not fly as high then as they do now, and the flight over, or rather through, the Rocky Mountains and down into Los Angeles airport was memorable. Like all early computers the SWAC took longer to build and com­ mission than was originally expected. Huskey was under pressure to state a date for its completion, and in the end he found himself saddled with the formal opening before he was quite ready. The demonstration program was the printing of a table of squares, generated by means of differences, since the multiplier was not yet working satisfactorily. The results were printed in hexadecimal notation with the most sig­ nificant digit on the right. I could not resist securing a copy of the output and sending it to Wheeler without explanation as a puzzle. However, these were matters that could easily be put right, and the SWAC was a most impressive machine. Although it worked in the parallel mode and used a Williams tube memory it was, in other respects, an interesting contrast to the Princeton machine. In particular, it had a four-address code instead of a single-address code, it was AC coupled, and had a logical adder carefully designed for fast carrypropagation. Huskey was, I think, the first person to understand prop­ erly this important aspect of the design of an adder for a parallel computer. Huskey once told me that when he returned from England to take up his appointment at the National Bureau of Standards, he at first proposed that the Bureau should build a machine along the lines of the Pilot ACE. This suggestion was not proceeded with, nor did Huskey return to it when he came to design the SWAC. However, a few years later he did design for the Bendix Corporation a machine—known as the G15 —which was distinctly reminiscent of the Pilot ACE although it used, instead of ultrasonic tanks, a magnetic drum with recirculating tracks. There was a small computer project at the University of California at Berkeley under Paul L. Morton and, when I arrived in San Francisco, I left my bag at the airline office and made my way to his laboratory. Morton was relying almost entirely on students to do the constructional work; progress was slow and the project did not have the impact it might have done. This was a pity because Morton’s ideas were quite sound. His machine had a magnetic drum as its main memory. The rest of my time in San Francisco was spent as a tourist. I was much taken by the city which, after Los Angeles, struck me as having its roots in the past. It was, in fact, just about to celebrate its centennial. I was lucky enough to catch up with the paintings from the Art Museum in Vienna which were on tour, waiting for the time when conditions would become normal enough for them to go back to their proper

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home. I had seen them earlier at the Tate Gallery in London, but my knowledge of painting had improved in the interval and I was very glad to have the opportunity of seeing them again. I flew to Boston on a night flight on Saturday 26 August, landing in Chicago on the way. This was then the usual thing to do, non-stop flights not having yet come in. I had timed my visit to Boston so that I could attend the International Congress of Mathematicians being held at Harvard University. Von Neumann gave a lecture on computers at the conference, but there was otherwise very little in the program that was of interest to me. Naturally I went to see Aiken who had, as I mentioned in the last chapter, moved the Mark I computer from the Cruft Laboratory to the new and specially built Computation Laboratory. It was located on the piano nobile in a large room with plenty of space opposite to it for another machine to be installed later. This room was, I suppose the first of the computer rooms to be built and appointed in the grand manner. Downstairs was a large open work area where the building of the Harvard Mark IV computer was proceeding busily. Aiken showed me around the building and told me about the work that was going on. The Mark I computer had just been fitted with a mechanism that would permit a conditional jump being made from one sequencing mechanism to another; Aiken regarded this as a great advance, although to most of us it was a puzzle why such a feature had not been built in from the beginning. I was, as I said in Chapter 13, when describing his visit to Cambridge in 1946, rather afraid of Aiken. He was very forthright in the way he stated his views, most of which I could not accept, at any rate without qualification. Fearing that an argument with him would lead nowhere and would perhaps become acrimonious, I tended to be rather careful about what I said. I am sure that many other people were equally reserved. Aiken knew perfectly well that his views were not universally accepted and was, I believe, puzzled by this general attitude of non­ belligerency. In fact, there was a look which would come into his eyes that I can now see was an invitation, almost a pleading, for his adversary to close in for a good sparring match. On that particular afternoon, in spite of all my resolutions, I did accept the invitation. He had been goading me about the binary system, for which he had no time. He thought it foolish to build a pure binary computer. I disagreed. He admitted that at the present time the binary system lent a certain simplicity to the design, but maintained that, once we really knew how to build a decimal machine, this advantage, for what it was worth, would disappear. I could not accept this either, and we were soon at

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it, hammer and tongs. Aiken was delighted to have found someone willing to take him on in argument, his heart warmed to me, and he took me round to his apartment for highballs and dinner. We were a small party; I remember that J. R. Bowman of the Mellon Institute was also there. I enjoyed the evening very much. Aiken was much my senior and a distinguished figure in the computer world. I felt flattered that he should have accepted me in this way, and I discovered that evening what a delightful companion he could be. Aiken’s achievements were very real. He was the first to propose and then, in collaboration with IBM engineers, to carry through the construction of a large scale automatic computer; he was the first to face the operational problems of putting such a machine to productive use. He was also a pioneer in computer education. But at the time of which I am speaking he was no longer looked to as a leader by those who were building the machines that are the ancestors of today’s computers. It was not only that he had isolated himself from the new ideas about machine structure—the idea of putting instructions and numbers in the same memory was anathema to him—but he had become technologically backward. This was partly a consequence of his background. In the years immediately before and during the Second World War, a whole new technology had come into existence, as­ sociated with ionospheric research, television, and radar; it was a technology of wide bandwidths and short pulses. This was the world in which I and others of my generation had grown up, and we saw the possibility of achieving, by these means, very high speeds with elegant economy of equipment. Very few people of Aiken’s generation developed green fingers for electronics, but not all were afraid of high speed electronics to the extent that he was. He just could not believe that devices like mercury memories would work, or rather that they would work reliably, for to him, if things did not work reliably, they did not work at all. In the very short term he was perhaps right, but in the longer term he was wrong. The consequence was that, to people like me, Aiken’s technological aims seemed very pedestrian. No doubt Mark III and Mark IV did good work for their sponsors in a narrow window of time when there was nothing else, but they represented the end of an era rather than the beginning. Aiken thought this too but for different reasons. I heard him give a lecture in which he described the various machines that had been built in his laboratory; he referred to Mark IV, then still incomplete, and then said, solemnly and impressively, that that would be the last machine to be built at Harvard. He went on to say that he thought the computer field was about to stabilize, by which I think

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he meant that computers would become one of the things that man­ ufacturers would produce, but that they would no longer be of special interest. One tends to think of Aiken and the Computation Laboratory—I am now speaking specifically of the time when the Harvard machines were being built—as though they were the same thing, and it is true that he dominated the place. However, he had one great redeeming feature. He did not, like many other dominating men, seek to surround himself with nonentities. He was a judge of people, and he chose for the staff of the Computation Laboratory outstandingly able men and women. He gave them, according to his lights, a sound training, and many of them have made their mark in the computer world. At MIT a very fast parallel computer, known as the Whirlwind, was being built, under the direction of Dr J. W. Forrester. The project was well backed and had an unusually able engineering staff including R. Everett. It was to have a significant influence on the development of the subject as a whole and in particular on the development of United States radar surveillance systems for air defence. I never knew anything of the military side of the project although, of course, the radar problems would have been of much interest to me. K. C. Redmond and T. M. Smith have told in their book, “Project Whirlwind: the History of a Pioneer Computer”, how Forrester and his colleagues originally in­ tended to build an analogue computer, and were gradually pushed towards a digital solution. By the time I knew them, they were pillars of digital orthodoxy, and I did not suspect that they had an analogue past. The Whirlwind computer was built in such a way that all the com­ ponents were immediately accessible, and in consequence it occupied an unusually large amount of floor area. The physical scale was, in fact, quite impressive and one could walk down the aisles between the digits. This was in spite of the fact that its specification was quite similar to that of a simple 16-bit minicomputer of a later period. In September 1950 the computer was working with the exception of the memory. This was to be based on specially designed cathode ray tubes, the principle of operation being quite different from that used by Williams. The tubes were being made in the Laboratory, and I was more than a little impressed by the fact that resources were available for a major development of this kind. While at Project Whirlwind I met Charles W. Adams, who was to become a close friend in later years. It was part of the plan to allocate a small share of the Whirlwind’s time for academic work at MIT, and Adams had been appointed to organize this activity. He was much

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interested in our experiences in Cambridge, and I needed little prompting to hold forth at length about subroutines and their assembly to make a program and about methods of error diagnosis. Other members of Adams’ group were Alan Perlis and John Carr. Carr had spent some weeks in Cambridge earlier in the year when on his way back to the States after studying in Paris. In a lecture given many years afterwards at the Computer Museum, then located in Marlboro, Massachusetts, Perlis recalled that Carr had been much impressed by the programming methods we had developed and had given an en­ thusiastic account of them on his return. I knew that Carr’s visit had been very successful but I had not realized, until Perlis mentioned it, how important it had been from the point of view of the transfer of ideas. The meeting of the Association for Computing Machinery was held in the Wardman Park Hotel in Washington a few blocks from the National Bureau of Standards. There was a remote demonstration of the SEAC using a teletype with an episcope arranged so as to project an image of the received material. I spoke on our operadonal experience with the EDSAC. Otherwise the emphasis in the program was on the way computers might be used in various areas of mathematics and mathematical physics, and on the impact that they would have. When I arrived in the United States in July 1950, the Korean war had just started. This event made a great impact on the American people and I was surprised at the extent to which war fever began to build up. By the end of my visit, it was being taken for granted that a general war was imminent and there was even some following for those who advocated a preemptive strike. One of my friends went out of his way to warn me that I should not take at its face value everything that I read in the press; nevertheless, the unanimity of the people I spoke to was remarkable and I received the impression, rightly or wrongly, that the general body of opinion supported the war policy of the government. At the end of the Second World War the United States and the United Kingdom found themselves in very different situations. The United States had come out of it with the feeling that they were now the most powerful nation in the world. They were willing to use their power, including their military power, to make things go in the way they wanted them to. The British on the other hand had been exposed in their homes to six years of enemy attack and had suffered privations on a scale quite unknown in the continental United States. They had no intention—and the same applied to their former European allies—of putting their economy back on a

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war footing, as some people in America seemed to think that they should. I travelled straight from Washington to New York and embarked on the Queen Mary for my journey home. When I last travelled in her in 1946, the Queen Mary was still in her wartime state with no division into classes. Now she was divided up again. One memento remained. Troops who had travelled in her during the war had carved their names on the teak rail encompassing the boat deck, and no attempt to remove them had been made. I travelled cabin class and, while this was spacious enough, I did miss being able to walk right round the boat deck. I had a rather stuffy and noisy cabin that I shared with a Turkish engineer who had been working on the design of the United Nations building at Lake Success. In the big liners of those days, if one travelled alone, one normally expected to share a cabin with a stranger, since single cabins were few and very expensive. This contrasted with the style of living and the general luxury of the public rooms, including the expectation that passengers would dress for din­ ner. I feel that, if the shipping companies had offered a simpler style with more privacy, they might have found, when the time came, that people would have been slower to transfer their custom to the airlines. It was during the trip that I have just been describing, and the few months that immediately followed it, that my ideas on the subject of microprogramming crystallized. We had tried to make the design of the control sections of the EDSAC as systematic as possible, but they contained a great deal of what is now called random logic. I felt that there must be a way of replacing this by something more systematic, perhaps along the lines of the conhguradons of diodes used for decoding the function digits and subsequently re-encoding them to drive various gates throughout the computer. My voyage across the Atlantic in the RMS Newfoundland gave me the opportunity to do some quiet thinking on this subject and later, when I saw the Whirlwind computer, I found that it did indeed have a centralized control based on the use of a matrix of diodes. It was, however, only capable of producing a fixed sequence of 8 pulses —a different sequence for each instruction, but nevertheless fixed as far as a particular instruction was concerned. It was not, I think, until I got back to Cambridge that I realized that the solution was to turn the control unit into a computer in miniature by adding a second matrix to determine the flow of control at the microlevel and by providing for conditional micro-instructions. Sometime during the winter the ideas fell into shape and I gave an impromptu lecture to my colleagues. I subsequently wrote them up and included them in a lecture that I gave in July 1951 to a conference held at

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Manchester University to mark the completion of the Ferranti Mark 1 computer. It was not very long before I was again in the United States. The Institute of Radio Engineers, the American Institute of Electrical En­ gineers, and the Association for Computing Machinery all had a stake in computers, and they combined their forces to organize a joint conference in December 1951. This was held in Philadelphia and was the first of the Joint Computer Conferences, a series that has continued to the present time, although for the last few years they have been known as National Computer Conferences. Several people, including myself, who were present at the first one, were also present at the one held 25 years later in New York City. This time I went by air, travelling in a Stratocruiser, a propeller driven aircraft with four piston engines. Air travel was not as reliable then as it has since become. I had booked a night flight and had duly reported at Heathrow to the longhaul terminal still temporarily ac­ commodated in Nissen huts on the north side of the airport. There was mechanical trouble with the aircraft, and I remember spending an uncomfortable night, sleeping as best I could in a chair in the lounge, and being woken up at two-hourly intervals to be told that the flight was delayed for a further two hours. We finally took off in the early morning and landed at Shannon. Here the aircraft was refuelled and the passengers were fortified with a hearty breakfast in preparation for the flight to Gander in Newfoundland. Shannon was quite famous for the quality of the entertainment that it offered to travellers, Gander being by contrast one of the dreariest places on earth. It seemed appropriate that I should be going back to Philadelphia where I had received my first exposure in depth to the new ideas. I spoke about the EDSAC and showed a short film that we had made a few weeks before. Making such a film was, in a way, a natural thing for us to do. Both Mutch and I had had some association with the unit at TRE responsible for making films for the training of air crew in the use of new radar equipment and Mutch, in addition, had had a good deal of experience in the production of amateur stage per­ formances. I wrote the scenario, Mutch acted as director, and Alexis Brookes, a colleague in the University Engineering Department, was the camera man. The film told a story. A. S. Douglas played the part of a mathematician who posed a problem, namely the evaluation of a definite integral. He explained the problem to a committee who then proceeded to discuss how it should be solved, in particular what subroutines should be used. J. C. P. Miller appeared prominently in

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this discussion. A programmer—played by S. Gill—was set to work to do the coding and the him then showed the various stages of the program being run on the computer and the results printed. In ret­ rospect, the him seems almost like a commercial for subroutines. Although a sound track was planned, this was not added, and when showing the him we were in the habit of providing a spoken com­ mentary. Twenty-hve years later, when there was a growth of interest in early computer history, I recorded an introduction and a com­ mentary, and the him was reissued with these added. During the conference in Philadelphia a number of informal dis­ cussions took place on the subject of programming techniques, and someone wrote a short account of them for the Proceedings. I men­ tioned an idea that I had had for what I then called free addresses, although the term floating address was later adopted in order to avoid confusion with another term in common use, namely, three-address. In early programs, instructions could only be referred to by their position relative to the hrst instruction of the subroutine in which they occurred. This meant that, during the process of debugging, it was frequently necessary to make changes to the addresses written in jump instructions and—in the days before index registers became usual— in many other instructions also. This was a major irritation to the programmer, and the source of much error. My idea was that the addresses should be written in symbolic form and translated to absolute form during input. Floating addresses will be recognized as a forerunner of labels. Adams became very interested in this and related matters, and he formed a plan for assembling a group of people at MIT in the summer of 1952 with the object of constructing a comprehensive programming system which became known as the CS. I suggested that Mutch would be a useful man to join this group and Adams invited him. Wheeler, who was on his way back to Cambridge from the University of Illinois, was also there and so was Gill, who was about to take Wheeler’s place. I was able to spend a short time with the group after attending a meeting of the ACM at Toronto in early September 1952. Later in the same month, Adams held the first of a number of summer courses on programming and we all stayed on to help with it. These courses were quite influential. On the first occasion the students did not have access to a computer, and the teaching was based on EDSAC programming techniques, the text book used being Wilkes, Wheeler, and Gill. The next course, held in 1953, was based on a specially designed (hypothetical) computer, known as the Summer

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Session computer, for which an interpreter was written to run on the Whirlwind. This was a very progressive thing to do in 1953. In 1952, I had crossed the Atlantic by sea rather than by air; this still seemed the more natural way and it was still cheaper. I sailed up the St Lawrence as far as Quebec admiring the beautiful scenery on the way, particularly as one approached Quebec itself. I was hoping to have time to look round the city but, unfortunately, the ship was late and I had no option but to go straight on to Toronto. I had been asked to speak at the conference and I had given as a title “Pure and Applied Programming”, intending to draw the dis­ tinction, then rather novel, between what we now call system software and application programs. The talk was mostly concerned with floating addresses and with synthetic orders, which were a form of macro. After the conference, Charlie Adams drove me to Boston by way of Niagara Falls where we spent the night. The Whirlwind Computer was then working with the CRT memory on which the original design had been based. Forrester never had any doubt that the development of this memory would be successful, and indeed it was. However, from an early stage he had his eye on some­ thing better for the future. When I first met him in 1950, he invited me to his home and, during dinner, began to tell me about his ideas for a coincident current magnetic memory, ideas that led eventually to the development of the core memory. I was fascinated by these ideas, which seemed so bold and so different from anything that had gone before; we sat long after dinner as the light began to fail, too absorbed in the discussion to think of switching on an electric lamp. I came away unable to make up my mind as to whether it was a pipe dream or a prophecy. Forrester’s paper on the subject appeared the following January. Forrester started a program of work with the co-operation of General Ceramics, who undertook to develop ferrite cores with suitable char­ acteristics. Success was clearly in sight by 1952. When I was there in August, Bill Papian, a graduate student working under Norman Taylor, had a small scale memory consisting of a single matrix of 16 x 16 cores running on test, and work on a larger one was actively proceeding. This work led to the construction of a memory of 2048 words, destined ultimately to be put on to the Whirlwind computer. For the purpose of testing this memory, what was known as the Memory Test Computer was put together; this was a complete stored program computer built from pulse control units made by Burroughs and based, I believe, on MIT designs. These could be connected together by means of coaxial cables in any desired way. Burroughs themselves

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had constructed an experimental computer from similar units and had demonstrated it in Philadelphia during the Joint Computer Conference in 1951.1 always remember that occasion as being the perfect example of one foolproof way to demonstrate a computer. The computer was programmed to print random numbers and, if this was not enough to discourage undue curiosity about the accuracy of the results, cocktails were served during the demonstration so that after a short space of time no-one cared any more. I was fortunate in being on the spot when the core memory, having passed all its tests with flying colours and much sooner than expected, was taken off the Memory Test Computer and put on to the Whirlwind. This was in August 1953 when Adams was running his second summer course and I had gone over on his invitation to help with the lecturing. I shall never forget the electric thrill that ran round the laboratory when the core memory had been running for a few days. With the electrostatic memory, parity failures had been common, averaging at least two a day. They hardly ever occurred with the core memory; when I returned I was able to report in a lecture to the Cambridge colloquium that there had been only three parity failures in three weeks. Overnight, the memory had ceased to be the least reliable part of the computer and become the most reliable. Moreover, the cycle time was only 8 micro-seconds compared with 30 micro-seconds for the electrostatic memory. The development of the core memory was a brilliant achievement. Norman Taylor, who was one of the engineers responsible under Forrester for the work, told me afterwards that he had fought to keep the system simple. The cores themselves were under development at the same time, and clearly they had to reach a certain level of quality and uniformity for a memory to be made at all. No-one knew how far the perfecting of the cores could go, and there were plenty of suggestions for complicating the system design in order to accom­ modate inferior cores. Taylor set his face against all such expedients and the final design was both simple and elegant. I have remembered this lesson when engaged on projects myself. While the work on core memories was proceeding at MIT, another program, which had been instituted independently by Jan Rajchman, was in progress at RCA. Shortly before going to MIT to take part in the summer session, I had visited the RCA laboratories in Princeton where Rajchman had shown me a matrix of 100 by 100 cores. In­ formation could be stored at all the locations in this matrix, except for one at which it was discovered on inspection that the core had been omitted by mistake. While we were having lunch, Rajchman

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asked me whether I thought that programmers would ever hnd a need for a memory as large as 10,000 words. I am glad to say that I unhesitatingly gave the right answer—I hope the one he was want­ ing—and I think that anyone who was actively immersed in pro­ gramming himself would have done the same. The fact that the matter should have been raised, however, is interesting and reflects the fact that technological advance generates a reaction tending to question the need for further advance in the same direction. Eckert, in a paper presented at a Computer History Conference held in Los Alamos in 1976, stated that in 1955 von Neumann had opposed putting more than 10,000 words of high speed memory on the UNIVAC LARC, asserting that this would be a waste of the government’s money. In the discussion that followed, Cuthbert Hurd confirmed that this was indeed von Neumann’s view and said that he had consistendy advised IBM against the development of large core memories, maintaining that it was sufficient to have a large backing memory in the shape of a magnetic drum.

17 EDSAC

As soon as operations with the EDSAC had settled down to something of a routine we naturally began to think about the next machine that we would build. I realized that this time formal funding in advance would be necessary and in January 1951, at Hartree’s suggestion, I approached the Nuffield Foundation. In support of my application I was able to say that automatic computing in Cambridge had passed the purely experimental stage and that its possibilities were being exploited by research workers in a good many different departments of the University. The whole operation was, however, dependent on a single machine which was never intended to be more than an ex­ perimental model. The serviceability of the EDSAC had varied greatly from month to month and even from week to week. At dmes it had been very good, but at other times it had been very bad. I put some emphasis on the importance of designing a machine with reliability and ease of maintenance in mind from the beginning. The response of the Trustees of the Nuffield Foundation was sym­ pathetic and prompt. By the middle of June 1951 they had agreed to give me exactly what I asked for, namely, a grant of £25,000 to be spent over five years. This figure was not, of course, calculated to represent the entire cost of the project, since the University met the ongoing cost of running the department, including the salaries of the permanent staff. Later, as I shall explain, a supplement of £10,000 was requested and agreed to. By the time the grant was made I had a fairly clear idea of what I wanted to do. I had come to realize that the economy of the serial mode of operation was more apparent than real. This is because the control circuits of a parallel machine are altogether very much simpler than those in a serial machine. Moreover, a parallel arithmetic unit could be designed so that it could be tested over a wide range of

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speeds, perhaps down almost to zero speed. This appealed greatly to anyone who had been used to a synchronous machine in which it was impossible to turn down the speed to see what was going on. A properly designed DC coupled machine in which every care had been taken to avoid time-constants should have little tendency to pattern sensitivity. In all this thinking, I owed much to Julian Bigelow at the Institute for Advanced Study, Princeton. In 1951 there was no clear answer to the question of what form of memory to use. The ultrasonic delay memory was well tried and reliable, but it was slow. The Williams tube memory, especially when used in the parallel mode, needed very careful engineering and even then acceptable performance could be obtained only by careful nursing. We had had no experience whatever in Cambridge of Williams tube memories and I felt a strong reluctance to become involved. The upshot was that we decided to go ahead on the assumption that we would build a parallel computer using an ultrasonic memory with one tank for each digit in the word. We were by no means happy with this decision since the computer would spend most of its time waiting for memory access. However, we felt that we could engineer such a machine so that it would work with a high degree of reliability and that, by using shorter tanks and a higher pulse rate, we could obtain a speed of some four or five times that of the EDSAC. Since we were, for the time being, stressing reliability more than speed, this was acceptable. We took comfort in the fact that the design of the machine would be such that a better memory could be fitted at some future time. By the summer of 1953 we were ready to begin building the arith­ metic unit and had done enough work on the design of improved mercury tanks and their associated circuits to go ahead with the memory also. We were, however, then beginning to receive exciting reports of the success of the core memory on the memory test computer at MIT and the feeling grew that this was the time for a major re­ appraisal. Mutch drew up a reasoned memorandum on the subject and, immediately before leaving for the United States on 17 August, I circulated this memorandum to members of the staff asking for their comments. I have already recounted the dramatic result of fitting the core memory to the Whirlwind computer and the deep impression that it made on me. When I returned to Cambridge towards the end of September, I reported what I had learned and from that time on there was no doubt that we should do our best to equip our new computer with a core memory. There were, however, two difficulties. One was that it would cost more money and the other was that it

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would take extra time. Accordingly on 3 November I went to see the Secretary of the Nuffield Foundation to explain the situation to him and to ask for a supplementary grant of £10,000. Again the Trustees were sympathetic and acted with speed; on 14 December I received a letter offering me what I had asked for. At this point the Mullard company in the person of J. H. Richards took a strong interest in collaborating with us with a view to developing magnetic cores that could be manufactured in Britain. Richards, whom I had known since he was an undergraduate in Cambridge and who was with me at RAF Dunkirk in 1939, was then on the staff of the Mullard Research Laboratories at Salfords. Although a research man, he exhibited much acumen on the business side. He set out to convince me that the company was capable of producing satisfactory cores and simultaneously to convince his superiors that it was worth their while to invest the necessary effort. Which of these two tasks he found more difficult I do not know, but he succeeded in both. Immediately after Christmas he took me on a visit to Mullard’s factory in Blackburn in Lancashire where various other types of magnetic ferrites were being manufactured on a large scale and where it was proposed that the magnetic cores suitable for computer memories would be made. We needed about 50,000 cores in all and I think that we settled on a price of lOd each. The cores were to be delivered to us untested, or virtually so, and we would select those which met our requirements. Testing was accomplished by passing a current, having an appropriate waveform, along a wire threaded through the core and observing the voltage induced in another wire similarly threaded. It was quite clear that the requisite number of cores could not be tested in a reasonable time without the aid of an automatic handling device for positioning the cores and putting the wires through them. We built a vibratory bowl of the type commonly used for feeding small components to automatic machines and found, somewhat to our surprise, that it worked perfectly. This was used to feed the cores to a work station at which a probe with two concentric conductors was inserted by means of a motor-driven mechanism. An operator observed the wave­ forms displayed on a screen and pressed one of two buttons according to whether the core was acceptable or not. The core then passed into the appropriate container and the next one came into position at the work station. There was a strong temptation, which we resisted, to try to make the testing completely automatic. By early the following year, the full number of cores had been received and tested and the matrices were being assembled. Through­ out we shared information fully with Mullard and, by the end of the

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exercise, they were in a position to offer tested cores of high quality to anyone who wished to buy them. EDSAC 2 was in a number of ways a working out of ideas I had put forward in the paper I presented at the conference held at Manch­ ester in 1951 to mark the inauguration of the Ferranti Mark 1 computer, and entitled “The best way to design an automatic calculating machine”. This paper introduced the concept of microprogramming and has often been referred to in that context. It was, however, also concerned with packaging, that is, the way the various gates and flipflops needed to make a computer should be grouped together to form physical units. I pointed out that, in the interests of easy design and maintenance, there should be as few different types of unit as possible. This led me to advocate a system for which much later the term bit-slicing was invented. I went as far as to suggest that identical physical units might be used both for the accumulator registers and the control registers. When putting forward the above ideas, I assumed that the registers and the adder would be interconnected via a bus, so that information could be transferred from any register to any other, through the adder if required. This is what is done in a modem micro-computer. When we came to design EDSAC 2, however, we found that it was difficult to do this, at any rate in a DC coupled processor, with the vacuum tube technology of the day. We, therefore, decided to provide a limited number of direct paths between the registers, choosing them as best we could for optimum performance. Since the requirements were different for control registers and arithmetic registers, this led to our abandoning the idea of using identical units for the two purposes; it is possible that reasons of economy would have led us to do this in any case, since certain operations, such as subtraction and shifting, were not required in the control section of the machine. David Wheeler returned to the Laboratory in September 1953 after three years at the University of Illinois. He was, unfortunately, too late to contribute to the decisions I have just been referring to, but he played a major part in what followed. He was responsible for the detailed design of the instruction set and of the microprogram. EDSAC 2 was the first large machine to be built with a control unit based on microprogramming. Everything in the machine was controlled by a single microprogram, including paper tape input and output, the operation of the magnetic tape decks, floating point arithmetic, and even the read-write cycle in the core memory. This was central to the economy of the design, since the provision of a microprogrammed control unit represented a large investment which it was important to exploit as much as possible. The read-only control memory consisted

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of a matrix of 1024 ferrite cores, these being much larger and having less exacting characteristics than the cores used in the high-speed memory. The matrix was about a metre square, and on two sides were the powerful vacuum tube drivers required to provide the current needed to switch the cores. To make a read-only memory at all was something of a tour de force in vacuum tube days, and it was for this reason that microprogramming did not become popular until transistors with their very much lower internal impedance became available. At first a very small control matrix was fitted. It had originally been intended that this would be used for engineering tests only, but David Wheeler, with characteristic ingenuity, managed to wire into it a mi­ croprogram for an instruction set that was actually usable, albeit highly restricted and distinctly odd. The machine in this form became known as EDSAC 1.5 and some practical use was made of it, notably by Joyce Bladder, who used it for her thesis work on stellar equilibrium. Some saw a connection between the success of EDSAC 1.5 and the fact that Joyce Bladder shortly afterwards became Joyce Wheeler. A feature of EDSAC 2 was the provision, in addition to the high­ speed core memory, of a read-only memory of similar size and speed. This was made of the same type of ferrite core and had permanently wired into it routines for commonly required operations. These included input and output (with the necessary binary-decimal conversion) and computation of trigonometrical routines; room was also found for a routine for integrating ordinary differential equations by the RungeKutta-Gill method. Since EDSAC 2 had a small high-speed memory and no magnetic drum, the provision of the read-only memory in­ creased its power significantly. A further feature that programmers found to be of great value was a trace facility incorporated in the microprogram. If a program were run with a certain key on the operator’s console depressed, a record would be kept of the details of the last 50 or so jumps that had occurred. A service program was provided which could be run when the program had stopped or had been stopped by the operator; this would analyse the record and print a concise description of the cycles and subcycles that the program had executed. The value of this facility in debugging assembly language programs will readily be appreciated. When it was in operation the machine ran at approximately one tenth of its normal speed. EDSAC 2 began to take some of the University computing load early in 1958. EDSAC 1 was kept going for a time while users were transferring their work to EDSAC 2 and was finally closed down on 11 July 1958. We were anxious to re-use the space that it occupied and most of the machine was sold for scrap. There are thus very few

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relics in existence and this we all now greatly regret. The most in­ teresting of them were later given to the Science Museum, London. EDSAC 2 had a memory of 1024 words. By the late 1950’s this was beginning to appear woefully small. It had by then become possible to purchase large core memories as complete units and I began, wistfully at first, but more earnestly later, to think what a difference it would make to our work if one could be obtained for EDSAC 2. It was about this time that Britain began to fall seriously behind the United States as regards computer progress, and one reason for this was the failure to go in for large high-speed memories. Christopher Strachey remarked to me one day that the availability of such memories in the United States meant that all the new ideas in programming were now coming from that country. In considering how we might add a large memory to EDSAC 2, we immediately encountered a difficulty which, as com­ puter memories got larger and larger, was to be encountered in the context of many other machines, namely that there were not enough address bits in an instruction. I was determined to get round this difficulty one way or another and, after much thought, I hit on a scheme involving a form of indirection that I thought might work. I put this to David Wheeler who, after some initial scepticism, came up with an improved variant of his own. There was general agreement that this would be satisfactory and the only problem that remained was to raise the necessary funds. I thought that in this case boldness would be the best policy and so I approached the General Board of the Faculties for a grant of £40,000. To my gratification and, I must admit, surprise, they approved it almost at once and in August 1961 we were able to announce to our users that a memory of 16,000 words would be available in early 1962. For a time this made EDSAC 2 almost unique among British machines and did something to convince people that large memories were both possible and desirable. At about that time Harry Huskey spent a term with us during which he interested me in portable language systems. This was a new subject in which he had done much pioneering work. He used for his ex­ periments a language known a NELIAC. This was a full scale language, and he had a team of students working on it. I conceived the idea of defining an elementary list-processing system that would be simple enough for one person to carry through the successive operations of definition, implementation, and transfer to another computer. It was based on a simple macro-generator—rather than a compiler—and I well remember my excitement when I first succeeded in making it generate itself. The system, to which the informal name WISP was given, became well known, and had quite a vogue as a student exercise.

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I myself learned a lot from it. Portable language systems were a long time in gaining general acceptance. In retrospect, it can be said that no very deep insights were necessary in order to write a portable system, but it was necessary to observe certain principles and to exercise some self-discipline when executing the actual transfer. The incom­ patibility of the character representations used on different computers caused a number of headaches which the general adoption of the ASCII standard has largely removed. The WISP project would have been quite impossible without the large memory. As a project it was very beneficial to me personally, since I had just emerged from writing a book and had allowed myself to get out of the swim of research. WISP started me off in a new direction. I adapted the macro-generator to various purposes and continued to use it for some years. The magnetic tape units on EDSAC 2, although built commercially, were a direct result of a program of work that I had started in the early part of 1952. I had realized, during one of my trips to the United States, that there was then no work at all going on in Britain on the use of magnetic tape for computer purposes. After some initial ex­ periments I designed, with the help of the workshop staff, a magnetic tape unit of advanced specification. The tape was moved at 100 inches per second by means of a pair of pneumatic capstans, one for each direction. The idea of the pneumatic capstan had originated at Harvard, where it had been applied to the design of input and output units in which the tape moved at low speed in one direction only. We had to learn how to make multi-channel magnetic heads with stampings we made ourselves. I had as a collaborator in this work D. W. Willis who had been on our staff in the early days and who had now rejoined the Laboratory after spending a year working for the Swedish Board for Computing Machinery in Stockholm and another year working for Ferranti Ltd. We connected an early version of the tape unit to EDSAC 1 via a shift register. The system did not work particularly well and contributed little to the operational use of the machine. It did, however, enable some practical experience to be obtained. In due course, Willis joined Decca Radar, taking with him the knowledge he had acquired while with us, and the result was the Decca twin tape unit. We purchased two of these for EDSAC 2, giving us four tape positions in all, and they gave very good service. The tape system was designed with its use as an auxiliary memory in mind; the tape was divided into addressable blocks, and information was written to and read back from these blocks. The passage under the head of a mark indicating the beginning of a block interrupted

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the computer and it was possible to cause the tape to be positioned ready for reading a particular block while computation was proceeding. In making use of addressable blocks, the EDSAC 2 tape system differed from other systems of the period in which a continuous sequence of words was written to and read from the tape, the end being indicated by an end-of-hle mark. The EDSAC 2 tape system was peculiar in that the tape units were adjusted so that the tape ran slightly out of contact with the head. This was my own idea. I was led to it because the tape of the period tended to have small lumps embedded in the oxide coating and these caused the tape to jump if run in contact with the head in the usual manner. Out-of-contact operation also avoided the considerable wear on the head resulting from the fact that the tape then available was very abrasive. I thought at the time that out-of-contact systems might become common. This was a short-sighted view. Under the pressure of the demand for high quality computer tape, the manufacturers refined their processes to the point at which tape virtually free of defects became available. Another development of the same period that had a commercial future was a high-speed photoelectric paper tape reader. This was capable of reading tape at the rate of 1000 characters per second and of stopping instantaneously with the next row of holes in position ready for reading. The tape reader was taken up by Elliott Brothers and must have remained in production for 15 years at least. With its broad, squat, nose-like hood over the lens, it was long a familiar object in computer rooms. In March 1958 John Kendrew and his associates announced the successful determination, by the methods of X-ray crystallography, of the structure of myoglobin, a protein found in animal muscle, where it provides a mechanism for the storage of oxygen. We had been able in the Mathematical Laboratory to share in the excitement of this remarkable piece of research, since the calculations that were needed were done on EDSAC 1. A total of 400 measurements of X-ray re­ flections were made and something over an hour of EDSAC time was needed for the final production runs; the resolution was just good enough to enable the general form of the structure to be made out. Kendrew and his team proceeded to a second determination at a higher degree of resolution, which involved the making of no fewer than 10,000 measurements. Fortunately, by then EDSAC 2 was running. The results were published in Nature in February 1960, alongside a parallel determination by M. F. Perutz of the structure of haemoglobin, the protein responsible for the transport of oxygen in the blood. The

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protein molecule is about four times as big as that of myoglobin, and turned out to be composed of four sub-units, each closely related to myoglobin. It was not only in their demands on a computer that Perutz and Kendrew were working at the limit of what was then possible. The myoglobin had first to be purified and persuaded to crystallize, many hundreds of measurements of the X-ray diffraction pattern had to be made—without the benefit of the automated instruments that were later developed —and original means had to be devised for determining phases, since it is a fundamental limitation of X-ray methods that only amplitudes can be measured. As the results of the first myoglobin calculations came from the computer they were plotted on sheets of transparent plastic, which were then put together to form a stack with correct spacing between the layers. No-one knew, until almost the very end, whether a clear structure for the molecule would emerge from an inspection of this stack or whether several years of sustained effort would have to be written off. Kendrew’s interest in the use of computers in X-ray crystallography went back to the early days of EDSAC 1, when he and John Bennett wrote what was, I think, the first paper on this subject. Kendrew remarked in a Nobel lecture, delivered in 1962, that the early Fourier syntheses of myoglobin data were, to the best of his belief, the first crystallographic computations ever carried out on a digital computer. He added that it was some years before other groups working in the subject began to use computers. The informal collaboration between Bennett and Kendrew was typical of the way in which computer applications were pioneered in Cambridge. X-ray crystallography illustrates very well the way in which new developments start under the umbrella of computer science, and later come to be viewed as computer applications pure and simple. At the time at which it was done, Kendrew’s work was regarded as of great interest to all computer people. In the summer of 1959, when the British Computer Society held a conference in Cambridge, it seemed entirely natural for Kendrew to give an invited address with the title “Why blood is red.” An entirely different field in which EDSAC 2 played a central role was radio astronomy. This work was based on the Cavendish Labo­ ratory and was under the leadership of Martin Ryle. Ryle had begun to work in the field immediately after the war, as a research student under Mr J. A. Ratcliffe. The radio telescopes built at Cambridge have all been of the synthetic aperture variety, in which signals recorded over an extended period —often weeks or months —are analyzed by a computer to give a contour map of the sky. From this map the

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locations of radio stars can be inferred. EDSAC 1 would not have been nearly powerful enough to enable a full two-dimensional reduction to be made, although it had been used for some one-dimensional experiments which had established the soundness of the method. On the other hand, EDSAC 2 had proved a very good work-horse for these reductions and some striking results had been obtained. However, although the computer took care of the calculations, the labour of plotting the results remained and was proving a severe handicap. A cathode ray tube connected to the machine on which diagrams could be drawn and photographed proved of some assistance, but its res­ olution was poor, and a large number of separate photographs had to be joined together to give a useful map. Just at the right moment, in the summer of 1962, I saw, at an exhibition in the United States, a demonstration of the newly announced Calcomp plotter. I was so impressed that, when I returned to England, I sent off an order for one, although I did not know where the money was to come from. Ryle and I hastily wrote an application to the Royal Society grants committee—not telling them that we had already spent the money— and fortunately they agreed. The plotter was a great success and was soon being used for all sorts of other work besides radio astronomy. One day Ryle came to see me to say that he was planning the erection of a much larger telescope and to ask whether the Mathe­ matical Laboratory could undertake to provide the computing support required. This was at the time when a more powerful successor to EDSAC 2 was in sight, and I was able to assure him that the necessary computing power would be available. Ryle remarked, again in a Nobel lecture, that the development of the aperture synthesis method had been closely linked to the development of more and more powerful computers and that it would be interesting to speculate how the work in Cambridge would have proceeded if computer development had been five years behind its actual course. Routine work for the radio telescope continued to have priority in the laboratory until the day came when a small minicomputer attached to the telescope could do all that was required. EDSAC 2 may, in retrospect, be said to have been a highly successful design. The instruction set and the programming system that went with it were the fruits of David Wheeler’s experience with EDSAC 1 and with the ILLIAC, and were popular with users. They included a system of floating addresses (labels) which was implemented by a method which has since been recognized as an early example of the

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use of a linked list. We have all since much regretted that we did not construct a transistorized version of EDSAC 2, and so give the design a longer life. As it was, EDSAC 2 was closed down, with appropriate ceremony, on 1 November 1965.

18 Can machines think a n d other topics

While EDSAC 1 and EDSAC 2 were my main preoccupations during the years about which I have been writing, there were naturally other subjects that claimed my attention. I would like in this chapter to say something about a few of these. It was towards the end of 1946 that the British public first began to hear about computers, which the press would insist on calling electronic brains. In November of that year, Lord Louis Mountbatten used this term to describe the ENIAC in an address he gave to the British Institute of Radio Engineers. Hartree wrote to the Times pro­ testing, but adding that it was true that an electronic calculating machine “can be set up in such a way as to exercise a certain amount of judgement”. He was challenged to explain exactly what this meant by a correspondent who observed that the left hand would seem to be giving back what the right hand had taken away. In a second letter, Hartree defended the use of the word judgement, but in terms so obscure that his readers can have been left litde the wiser. In spite of all protests, the press continued to use the term electronic brain, along with certain variants, for example, mechanical brain and giant brain. This, together with the general use by computer designers of terms —such as memory—based on physiological analogy, made some people jump to the conclusion that the claim was being made that computers were something more that mere machines. The matter surfaced in the press in June 1949, when Sir Geoffrey Jefferson, Pro­ fessor of Neurosurgery at Manchester, delivered the Lister Oration to the Royal College of Surgeons, taking for his title “The Mind of Me­ chanical Man.” Jefferson evidently thought that dubious statements were being made and that he should refute them. His flights of rhetoric about machines not being able to write sonnets and know that they had written them, of feel emotion, were eminendy quotable and were

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a gift to the press. “When we hear it said that wireless valves think,” he said, “we may despair of language.” Turing was asked for his comments. What he actually said will never be known, but what came through in the Times was that the main preoccupation of the University of Manchester was to find “the degree of intellectual activity of which a machine was capable and to what extent it could think for itself.” This was too much for Dom Illtyd Trethowan of Downside Abbey who wrote to the Times ex­ pressing the conviction that all responsible scientists would be quick to dissociate themselves from this work; he mentioned Butler’s Erewhonians who felt the necessity to guard themselves against the possible hostility of the machines and stated his own belief that men are free persons. In the true traditional style of Times letter writing, he ended by demanding to know how far Turing’s opinions were shared, or might come to be shared, by the rulers of the country. It is hard to convey to the modem reader the seriousness with which this debate, which was after all no more than a debate about the use of words, was regarded by all sorts of people. Some people appeared to regard it as an impious act even to attempt to construct a computer. I felt that it was hard enough to have to struggle with the task of making “wireless valves” act like binary switching elements without having to fend off attacks of that kind. In order to understand the emotion that was released, it is, I think, necessary to remember two things. In the first place, computers ex­ hibited a behaviour far more complex than was exhibited by the simple automatic machines with which people were familiar up to that time. The result was that to a non-scientist a computer appeared like magic. It dazzled him, and he was all too ready to believe that it differed from other machines in more than degree. In the second place a discussion about how far a machine can go in imitating human beings can easily turn into a discussion about whether the human brain is to be regarded as nothing more than a machine; this raises religious and ethical issues about which human beings have long argued and felt emotion. A practical consequence of the debate was that, in self defence, many computer people, especially those working in industry, began to avoid as far as possible the use of terms that might be misunderstood; in particular, they would use the term store instead of memory. It was a pity that Turing had helped to excite the clamour in the press, because his views on calculating machinery and intelligence were well worth listening to. He set them out at some length in a paper which appeared in Mind in October 1950. I found this paper

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both witty and illuminating, although I remember that, when he re­ sponded to my request for a reprint, he remarked that he was not very pleased with it. The main thrust of his argument was to identify intelligence with the power to leam. It was easy to see how simple learning programs which would enable the computer to leam some specific thing could be written; I thought that perhaps, when a number of such programs had been written, a generalization would suggest itself. This did not happen, and the breakthrough is still awaited. Arthur Samuel, who became well known for his work on programs for playing draughts (checkers), confessed to me much later that he too had hoped that he would be the one to make the breakthrough. I wrote several articles explaining my position, the first being published in the Spectator in August 1951. It was as a result of the earlier correspondence, published in the Times in 1946, that my interest in Babbage was first aroused. Hartree had remarked in his second letter that, although the ENIAC was an electronic computer, there was no reason why the power to exercise judgement should not be possessed by a purely mechanical device. Lt-Cmdr Gould wrote pointing out that in the first half of the nineteenth century Babbage had proposed a machine which would have had just that property. This caused Hartree to refer to Babbage’s autobiography, “Passages from the Life of a Philosopher”, published in 1864, where he found that Babbage had himself used the word judgement to de­ scribe the action that is necessary in performing certain types of cal­ culation. I remember him coming into the Mathematical Laboratory with a copy in his hand and showing us the paragraph in question. When Babbage died his son, Henry, presented some twenty bound volumes containing his father’s correspondence to the library of the British Museum, now known as the British Library. At the same time he deposited his father’s scientific notebooks and other papers, together with some surviving artefacts, in the Science Museum. In May 1949, the curator of the Mathematical Instruments collection, whom I knew quite well, had them brought out of store for me to see and I spent an extremely interesting day studying them. Babbage had devoted the greater part of his life to working on the machine that he called the Analytical Engine, but never came within measurable distance of building it. He published, or rather helped L. F. Menebrea and Lady Lovelace to publish, some detailed information about how the Analytical Engine would be used, but he published extremely little about the mechanical contrivances that he would use to implement it. A case in point is cany propagation in an adder. In his book he describes the great excitement he felt when he discovered

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the principle of what he calls anticipatory carriage. This enables the carry to be propagated much more quickly than if it is passed suc­ cessively stage by stage. However, he did not go into the mechanical details. When I examined his notebooks, I was delighted at being able to locate the relevant entries and to see exacdy what it was he proposed. Two days after I paid this visit to the Science Museum, the EDSAC performed its first calculation, and from then on I had little time or thought for anything else. My interest in Babbage’s work continued, however, and in the introductory chapter of a book on computers that I published in 1956 I gave what was probably the most detailed account of it that had appeared in modem times. This account was based entirely on printed sources. When the centenary of Babbage’s death was approaching, the British Computer Society and the Royal Statistical Society conceived the idea of holding a joint meeting in London to mark the occasion. This took place on 10 October 1971. I was invited to speak on “Babbage as a computer pioneer”. I accepted this invitation with alacrity, realizing that it would give me the impetus to go back to Babbage’s notebooks and make a proper study of them. When I did so, I was taken aback at the wealth of material that they contained. The lecture in which I incorporated the results of my researches was published by the British Computer Society and later reprinted in Historia Mathematica. Babbage uses the term store, but refers to the arithmetic unit as the mill. In his published work he says very little about the control unit of the Analytical Engine; he does not, as Hartree first pointed out, even have a term for it. However, in his notebooks he calls it the directive part, and it is clear that he had given it deep thought. Here I made an interesting discovery. The machine that Babbage was de­ signing was, of course, purely mechanical and the problems that he was facing were quite different from those that later faced the designers of electronic computers. Nevertheless, the solution that he proposed for the design of the directive part can be regarded as a mechanical version of microprogramming in that it was based on the use of a read-only memory consisting of a cylinder, or barrel as he termed it, on which projecting studs were mounted at appropriate places. Babbage even saw the need for conditional micro-operations. In view of my own work on microprogramming, it is remarkable that it should have fallen to me to bring to light this aspect of Babbage’s work. Babbage wrote his autobiography late in life when he had at last come to realise that he would never complete the Analytical Engine. He makes a remark to the effect that one day someone will succeed where he has failed, and that only then will his work be fully understood

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and its value appreciated. It was certainly the case that the pages of Babbage’s notebooks were of captivating interest and full of meaning to me, reading them after digital computers had become a reality. They can have meant very little to those who tried to make something of them at an earlier epoch. This is especially true of the entries which deal with the control, but it is also true of those which deal with the design of the purely arithmetic part of the engine. Babbage discusses scales of notation, hoarding (that is, storage) of carries when successive additions are being performed, the use of precomputed multiples in multiplication, and much more. In 1837 Babbage wrote an account of the Analytical Engine as he then conceived it. This account has every appearance of being intended for publication, but it was in fact never published. Babbage must have given the manuscript to his close friend H. W. Buxton, since it is included among the Buxton papers in the Museum of the History of Science in Oxford. I came across a draft among the papers in the Science Museum, but it was only a draft of the early part and I searched in vain for more. If I could have seen the complete manuscript before I prepared my lecture, it would have been of great assistance to me. The paper has since been printed by Randell in “The Origins of Digital Computers”. Also among the Buxton papers is a brief note that Babbage made on 26 March 1839 about a project for writing a book to be entitled “The Science of Number reduced to Mechanism”. One can only make guesses as to why he did not publish the Buxton manuscript or proceed with this later proposal. I am inclined to think it was because he felt that before he published his ideas, he should demonstrate their sound­ ness by actually building the Analytical Engine. If this was the case, I can sympathize, since I have had similar feelings myself. There is no doubt in my mind that if Babbage had published a proper account of the material in his notebooks his reputation would have stood much higher than it did. I believe also that his work would have contributed to the modem development of computers instead of being unknown, except in general outline, when the critical advances were being made. My work on the Babbage collection in the Science Museum intro­ duced me to the fascination of doing historical research among the primary sources. Since then I have lost no opportunity on my travels of seeking out and examining unpublished Babbage material. It is not generally appreciated how extensive are the facilities made available in the universities and libraries of the world to historians. In scale they must be comparable to the facilities available to researchers in pure science.

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Babbage had an extensive circle of correspondents and letters written by him are to be found in libraries all over the world. I had a striking illustration of this when I visited the Huntington Library in Passadena in company with H. S. Tropp, who was at the time working on an AFIPS computer history project and was affiliated to the Smithsonian Institution. We had spent a hard morning working on computer history and had gone to the Huntington Library, which is also an art museum, to relax. Tropp introduced himself to a member of the staff who was good enough to show us over the research facilities. Hearing that I was interested in Babbage, he checked the catalogue and was able to produce for my examination no fewer than four letters in Babbage’s hand. There is a good deal of human as well as scientific interest to be found in Babbage’s life. The story of his association with the Countess of Lovelace has appealed to many, although I fear that the level of her mathematical attainments has been exaggerated. My own interest in Babbage led me to an interest in his sons, two of whom, Herschel and Dugald, migrated to South Australia while one, Henry, entered the military service of the East India Company. Henry spent his whole working life in India, serving during the later part of his career in several civil appointments, while remaining an army officer. When, after the Mutiny, the Crown took over the government of India from the East India Company, it fell to Henry, as senior office in the place where he was stationed, to read the Proclamation. He records that he did not feel very joyous on the occasion, for he preferred the rule of the Company, which he knew, to that of the Queen which he did not. A few years ago, I felt the urge to express in dramatic form my assessment of Babbage’s character and personality by writing a oneact play. The moment in Babbage’s life that I chose to portray was the one at which Henry and his wife Min were about to return to India after three years’ furlough spent living in Babbage’s house in London. The play was performed by a professional cast at the Computer Museum in Marlboro, Massachusetts, just before Christmas 1982. By the late 1950s, the public were better informed about computers that they had been, and the role of computers in business and scientific life was becoming established. Those years saw the formation, almost concurrently, of the British Computer Society and the International Federation for Information Processing. I was deeply involved in both these developments. People differ in their attitudes to technical and professional societies. I have throughout my career found them most valuable, both for the

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contacts they have enabled me to make and for the technical infor­ mation that I have acquired by attending meetings and conferences. There is, however, the danger that, if one becomes too heavily involved, one may be led to neglect one’s rightful duties or to fall out of touch with current research. This was brought home to me early in my career when I was serving on one of the main Section Committees of the Institution of Electrical Engineers (IEE). It was a Wednesday afternoon and I was attending a meeting of a subcommittee. The man sitting next to me chanced to remark—and there was a note of concern in his voice —that he had not been in to work that week, having spent all his time at the IEE! Having thus seen the red light, I decided not to seek any extension when my term of service on the Section Com­ mittee ran out. However, I have warm feelings for the IEE and I have since served as Chairman of the East Anglian Sub-Centre and as an elected member of Council. The coming of computers brought together people from many dif­ ferent academic disciplines and from many different walks of life. Many of these people were loyal members of one or other of the many learned societies or professional bodies —such as the IEE—that had an interest in some aspect of computer design or operation. How­ ever, as time went on, those whose main work was with computers began to feel the need for a specifically computer-oriented body which would enable them to meet others similarly placed and exchange ideas with them. In Britain the first moves towards the formation of a computer society took place in the middle 1950s. It was at first hoped that the new society could be set up with the good will of the older societies, and a meeting was called to which they were invited to send representatives. I attended this meeting and found it an un­ comfortable occasion. Remarks sympathetic to the formation of a computer society were made by David Brunt, Physical Secretary of the Royal Society, but otherwise the existing societies were united in making it clear that they would not welcome an interloper in their ranks. They recognized that the computer field cut across disciplines, but urged that, instead of a new society, there should be set up some kind of coordinating body which could sponsor joint activities. In the event both things happened; the British Computer Society was formed and at the same time a body called, somewhat misleadingly, the British Conference on Automation and Computation (BCAC) was established. It is fair to add that, once the British Computer Society had come into existence, not only were its relations with other societies cordial, but it became itself an active member of BCAC.

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A leading role in the founding of the British Computer Society was played by the London Computer Group, an organization composed mainly of people interested in business data processing. This group merged itself into the new society when it was formed and provided the initial nucleus of members. I was invited to become the first President of the British Computer Society and held that office from 1957—60. Dudley Hooper, chairman of the London Computer Group, became Chairman of Council and later also served as President. The British Computer Society grew steadily and there was no doubt that it filled a need. BCAC did not fare so well. In one sense setting it up was an imaginative action, since it covered automation as well as computing in the narrow sense and included a wide variety of organizations, ranging from the engineering institutions on the one hand to the Institute of Chartered Accountants and the Trades Union Congress on the other. It suffered initially from an over-elaborate organization, but this was corrected and the name was changed to the United Kingdom Automation Council (UKAC). For a time the chances appeared good that the UKAC might have a role to play in forwarding the cause of automation and computing in British industry. However, this did not happen and eventually it was wound up. The people who took the lead in establishing the British Computer Society were, as I have said, people who, for the most part, already had affiliations to one or other of the established professions. However, as time went on and the computer held expanded, large numbers of men and women began to make their careers in computing without having a background in another subject. The result was a strong pres­ sure on the Society to establish standards of membership and to trans­ form itself into a professional society that would cater, as far as Britain was concerned, for this new body of computer professionals. This was successfully accomplished. In the United States the Association for Computing Machinery had been formed as early as 1947, operating first as an informal organization on the East Coast. I joined as soon as I heard about it in order to receive the duplicated material that was sent to members from time to time. This was before the publication of a regular journal was undertaken. In 1951, the National Joint Computer Committee was set up to organize the series of Joint Computer Conferences that I referred to in the last chapter. These proved very successful and a feeling grew up in the United States that the time was ripe for a Computer Con­ ference to be held on an international scale. Accordingly, in 1957, the Joint Computer Committee asked Isaac L. Auerbach to write formally

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on its behalf to UNESCO in Paris making the suggestion that UNESCO should take responsibility for organizing such a conference. UNESCO agreed and invited a number of consultants from various countries to assist it in the task. I was one of these consultants and so was Auerbach. It was not long before the consultants began to discuss among themselves the possibility of forming an international federation. By common consent, Auerbach took the chair at the first of these dis­ cussions and continued to do so subsequently. My association with the International Union of Geodesy and Geophysics had given me some small feeling for what an international federation ought to be. Generally speaking, however, we were very inexperienced in such matters. Fortunately the member of the UNESCO secretariat who was responsible for our conference was able to give us a lot of guidance. Membership of the proposed federation would be open to societies— or groups of societies —that could claim to represent computing in­ terests in their respective countries. I was at first much worried by the fact that I did not have a mandate from any society in the United Kingdom for the negotiations that I was conducting. However Auerbach confided to me that he did not have any authority either and this made me feel better. We were in fact all in the same position. To my gratification, when the time came, the British Computer Society felt able to take on the commitment of subscribing to the new federation; this was a courageous act, since it was taken at a time when the society’s own finances were far from secure. The UNESCO conference was held in Paris in June 1959. While it was taking place, we held a meeting of people interested in the for­ mation of an international federation. At this meeting the draft statutes that we had drawn up were explained and discussed. These statutes were to come into force if they were ratified on or before 1 January 1960 by national societies in at least seven countries. So thoroughly had the way been prepared that, by the appointed day, representative societies in not seven but in thirteen countries had signified their adherence and the International Federation for Information Processing (IFIP) came officially into existence. Auerbach was elected the first President. I continued to represent the United Kingdom on the IFIP Council until after it had successfully organized its first Congress in Munich in 1962. I then indicated that I would like to retire and the British Computer Society appointed Stanley Gill in my place. Gill had been with me to one or two Council meetings and was eminently suited to work of this sort. I stood down partly because I wanted to have time available for other things and partly because I genuinely felt that

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it would be good for the Council to have some new blood, particularly as the founding members had been in the first instance selected by UNESCO and not by their national societies. Most of the other original members of the Council continued to serve and I had the pleasure of meeting them again when I attended the tenth anniversary luncheon held in Amsterdam in 1970. Apart from attending the Congress held in Edinburgh in 1968 and the luncheon in 1970,1had no further contacts with IFIP until I agreed to serve on the program committee for the Congress that was to be held in Stockholm in 1974. This was an onerous but enjoyable task. I was in charge of the hardware section of the program, and was responsible for arranging for the refereeing of several hundred sub­ mitted papers. W. M. Turski of Warsaw, who was in charge of software, had an even heavier load than I did. The chairman of our committee was H. Freeman, and we held meetings in Paris, Sophia, Stockholm, and London, each meeting lasting several days. In 1965 I was asked by Frank Yates if I would consider becoming Chairman of a computer advisory committee that the Agricultural Research Council (ARC) was about to set up. The ARC was a gov­ ernment agency whose role was to support agricultural research in the United Kingdom. It coordinated the activities of, and gave financial support to, a wide range of research establishments, some dealing with animals and some with crops. Some of the establishments had existed for a long time and enjoyed varying degrees of independence, while others were wholly financed by the ARC. One of the former was the Rothamsted Experimental Station which could claim to be the oldest agricultural research establishment in the world. The ARC had to its credit many notable achievements in plant and animal breeding, and it had fostered many innovations in crop and animal management. At the same time it had a high reputation for pure research in the underlying sciences. Frank Yates, whom I knew well because he had succeeded me as President of the British Computer Society, had been up at St John’s in Cambridge before my time. As a young man he had gone to work at Rothamsted where R. A. Fisher was building up a strong reputation in statistics as applied to agricultural research. When Fisher left to succeed Karl Pearson at the Galton Laboratory at University College, London, Yates succeeded him as head of the Rothamsted Department of Statistics. When I got to know Yates he was a staid and respected figure. There was, however, in his manner a certain impishness which was perhaps only discernible to those who knew him well. In his student days he had been addicted to a form of sport—if it may be

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called that—which had a long tradition in Cambridge. It consisted in climbing about the roofs and towers of the college buildings—partic­ ularly the old buildings —at night, the satisfaction arising partly from the difficulty of the climbs themselves and partly from the excitement of escaping the vigilance of the college porters. The chapel of St John’s has a very massive and imposing neo-Gothic tower designed by Gilbert Scott. This tower is adorned with statues of saints and to Yates it appeared obvious that it would be more decorous if these saints were properly attired in surplices, and so one night he climbed up and did the job. Next morning the result was generally much admired. The College authorities, however, were unappreciative and began to con­ sider means of divesting the saints of their newly acquired garments. This was not easy, since they were well out of reach of any ordinary ladder. An attempt to lift the surplices off from above, using ropes with hooks attached, was unsuccessful, since Yates, anticipating that this might be tried, had secured the surplices with pieces of wire looped round the saints’ necks. Little progress was being made and eventually Yates came forward and, without admitting that he had been re­ sponsible for putting the surplices up, volunteered to climb up in daylight and bring them down. This he did to the admiration of the crowd that assembled. I much enjoyed my association with the ARC; it provided a window on a whole way of life of which I would otherwise have been quite ignorant. Many of the establishments were located in country houses which, with their surrounding land, had come on the market when their owners found it impossible to maintain them. I looked forward to my visits to these establishments, where I could rely on being well received since they all had ambitions in the computer direction. In many cases the houses were of some interest from an architectural point of view. In Babraham, a village near Cambridge, was the Institute for Animal Physiology, where much fundamental research was being done. To those who only saw cows grazing contentedly in a meadow, it came as a surprise to see one standing, with apparently equal content, in a calorimeter, where it served as the subject for an experiment in metabolism. At the time of my first visit to Babraham, they had gone one better and were doing similar experiments with a lama. I met an earnest young research worker from Texas who was spending the summer there, He remarked to me on his good fortune at striking such an exceptional experimental opportunity. It appeared that very little was known about the metabolism of the lama, and that nowhere else in the world was one to be found in a calorimeter. Another

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intriguing item in the Babraham research program included a reference to the electric organ. This was not, as might be thought, an incursion into musicology, but referred instead to the shock-producing organ of an electric eel. I was shown two of these large creatures lying motionless at the bottom of a tank of water. I was invited to put my arm in and stir them up, but I had had quite enough electric shocks in my time and I declined to do so. Another ARC establishment near Cambridge was the Plant Breeding Institute at Trumpington. This establishment had been very successful in breeding strains of wheat with much improved yield. The widespread adoption of these strains had been a major factor in turning Britain from being a net grain importing country into a net grain exporting country. However, the plant breeder cannot afford to rest on his laurels, since new varieties, when they are introduced, are apt to become the victims of disease. A continuous breeding program is, therefore, necessary in order to produce further varieties that are immune to whatever the current disease may be. The Plant Breeding Institute was taking advantage of a recently discovered fact that the growing season of plants is determined by the duration of the day, and can be lengthened by the use of artificial lighting. People driving from London to Cambridge at night would see the blaze of light coming from the glasshouses, and those not in the know were apt to complain about the waste of public money that it apparently implied. When I first became associated with the ARC, computers were being used almost exclusively for statistical calculations, although later on data bases, data logging, and modelling began to assume importance. In agricultural research the statistician is to an experiment what the accountant is to a company; he is present at the birth, life, and death. In other words, statistical advice is necessary when an experiment is being planned, when the data are being collected, and when they are being analysed. Statistical computing services for the ARC establishments in England were provided by a computer centre at Rothamsted under D. Rees, who also acted as technical secretary of my committee. The computer centre had originally formed part of the Department of Statistics and still worked very closely with it. Statistical software was still in an embryonic stage and new statistical programs were continually being developed. Since the service was centralized these programs and im­ provements to old ones were immediately available to the establish­ ments. In Scotland the computing service was provided by the Edinburgh Regional Computer Centre based on the University. There was a small statistical research unit under Professor D. J. Finney which

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was available to give advice and to investigate special problems and also to provide liaison with the statisticians at Rothamsted. This pattern persisted during the whole of the time that I was chairman of the Advisory Committee, although there was a trend for the larger es­ tablishments to acquire small computers of their own. Since I retired as chairman in 1976, the availability of low-cost computers and de­ pendable statistical packages has made decentralization both possible and desirable. The range of the research that was being conducted in the various establishments of the ARC was very wide. I was fortunate to become associated with it at a time when computers and the kind of automation that they make possible were beginning to play a significant role. I was sorry when, after ten years, my term of office as Chairman of the Committee came to an end.

21

Logged in to the CTSS from Joe Weizenbaum’s study in Concord, Mass. In the summer of 1964 a scene like this was very rare

22

A windy day in Oxford in 1964. With Roger Needham, just before demonstrat­ ing the CTSS by trans-Atlantic telex to a Medical Research Council group

23 With E. Goto in Tokyo, 1975

24 Taken in 1975 at the opening of a new Computer Gallery at the Science Museum in London. From left to right: (standing) D. W. Davies, T. H. Flowers, Grace Hopper, J. H. Wilkinson, T. Kilbum, T. R. Thompson, M. V. Wilkes, C. Marks, A. W. M. Coombs; (seated) Elaine Hartree, F. C. Williams, M. H. A. Newman, J. D. Wheeler, K. Zuse

25 Roger Needham and David Wheeler explaining the Cambridge Ring to HRH the Duke of Edinburgh, Chancellor of the University, when he visited the Computer Laboratory on 8 January 1979

26

Philadelphia, 5 November 1982. From left to right: Nina, Margaret (our daugh­ ter), John Brainerd, myself, Kay Mauchly. I was about to receive an award estab­ lished in memory of Harold Pender, Dean of the Moore School, who sent the telegram inviting me to attend the course on electronic computers held in 1946

19 Computer progress 1955—8 0

In the early years, we were all fully occupied with immediate tasks and much of our time was taken up in struggling with unreliable hardware. However, there was no shortage of ideas waiting to be worked out when computers became better and people found the necessary time. To illustrate this, I might mention a “fun” program someone wrote to run on the EDSAC very early in its life. The EDSAC had a cathode ray tube monitor on which could be displayed, in the form of a matrix of 35 by 16 dots, the contents of a selected tank in the memory. It was not long before an ingenious programmer used these dots to make a primitive picture. In the program I am describing, a vertical line of dots in the centre of the screen represented a fence; this fence had a hole in it that could be in either the upper or lower half of the screen, and by placing his hand in the light beam of the photo-electric paper tape reader, an operator could cause the hole to be moved from the lower half—its normal position—to the upper half. Periodically, a line of dots would appear on the left hand side of the screen, and move slowly towards the right. These dots were controlled by a learning program that would initially cause them to appear randomly in the upper or the lower half of the screen. If they met the hole in the fence, they would pass through; otherwise they would retreat. If the operator moved the hole from top to bottom in some regular way, the learning program would recognize what was going on, and after a short time, the line of dots would always get through the hole. No-one took this program very seriously, but it contained the germs of computer graphics, man-machine interaction, and artificial intelligence. At that time, we were all too conscious of the gap between what we could imagine and what we could implement with vacuum tube electronics. Hardware was a nightmare, and sometimes we despaired.

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We prayed that things might become easier, but the boon we sought above all else was to have equipment whose normal state was to be working instead of broken down. But we had faith, and we have been rewarded as no band of devotees has ever been rewarded before. What made computer electronics different from traditional elec­ tronics was its use of random access memory, and the one single development that put computers on their feet was the invention of a reliable form of memory, namely, the core memory. The mercury memory was clearly an expedient to get going, and the Williams tube memory, while it saved the day, was only a stop-gap. But the core memory transformed the situation. Its cost was reasonable, it was reliable and, because it was reliable, it could in due course be made large. One thing that large memories made possible was the development of high level languages. The contemporary term for this field was automatic programming; the term has since been re-used to mean something else, but I shall use it with its original meaning. One day the history of the early gropings towards high level languages will be sorted out, although the necessary research will not be easy, since much of the work was not fully published at the time. The conference proceedings of the period are not as helpful as they should be, many of the papers being published in abstract only. Regrettably the Cambridge Laboratory played very little part in the development of automatic programming, although I personally fol­ lowed what was going on with great interest. Manchester, on the other hand, was the scene of some very original work on the part of A. E. Glennie, who was a member of the staff of the Armament Research Establishment, but who spent much of his time at Manchester working on the Ferranti Mark 1 computer. Glennie had received his early introduction to computers in Cambridge, where he spent some months soon after the EDSAC went into service; he is one of those listed in the preface to Wilkes, Wheeler, and Gill as having contributed to the original library of subroutines. Glennie developed a system known as Autocode which was, in effect, a simple high level language in which programs could be written for subsequent compilation into machine language. It is perhaps sig­ nificant that, although the Ferranti Mark 1 had a high speed memory of only one thousand words, it had a drum which was very advanced for its day, being both reliable and convenient to use. In consequence, programmers tended to regard the drum as the real memory in which they would keep programs and data, bringing them into the high speed memory only for running. This made the machine much better

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adapted than most of the other early machines were to the running of large programs and it would have been much more difficult for Glennie to have done his work on the EDSAC. Glennie reported on his system at a meeting of the Cambridge colloquium held as early as 29 January 1953. The subject of automatic programming was considered important enough for a session to be devoted to it at the ACM meeting held at MIT from 9 through 11 September 1953, and I was invited to take the chair. The list of the members of the panel, with their affiliations, as given in the conference program, is: John Bennett (Ferranti, Ltd), N. Rochester (IBM, Poughkeepsie), Grace Hopper (Remington-Rand Univac), C. W. Adams (MIT), S. Gill (Mathematical Laboratory, Cam­ bridge, UK), D. J. Wheeler (University of Illinois), and J. W. Carr (University of Michigan). I believe that most, if not all, of these people were present, but at this distance of time I cannot be sure. It is unfortunate that no record of the afternoon’s discussions, which were lively and sometimes even heated, has been preserved. Computer users, under pressure of the great need they felt to take the sting out of programming, were experimenting with various interpretive systems. None of these were entirely satisfactory and all of them represented a very inefficient use of the computer. The participants in the session divided quite sharply in their opinions. There were those who felt that all attempts to side step the real and eternal difficuldes of programming were misguided, and that more progress would be made if program­ mers kept to their real job of application programming. On the other hand, there were those who saw the new techniques as having a real and very practical value. John Carr made a rousing speech on the side of the latter. Programmers, he said, were divided into different sorts. At one extreme there were the primitives, to whom octal or hexadecimal represented an orthodoxy from which one only strayed at one’s peril; at the other extreme there were the space cadets — remember this was before the days of space travel—who saw them­ selves as about to become the inheritors of a brave new world. I hastened to enrol myself as a space cadet, making, however, the proviso that the true future lay with compilers rather than with interpreters. Among the most vociferous on the other side was Herb Grosch, who was then running some sort of computer operation. He deplored the way people stopped doing real programming as soon as they got good at it and dissipated their efforts in devising fancy interpreters and other such vanities. He for one would make sure he kept his programmers with their noses to the job of real programming. He

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had gone on in this vein for some time when someone asked him whether he would object if the computer manufacturers were to provide programming systems with their machines, so that all his programmers had to do was to use them. This brought him up short, and he appeared as one who had seen a bright light. While I do not think I would ever describe Herb Grosch as a space cadet, it is certainly true that his conversion to automatic programming started that afternoon. On my return home, I tried to convey to my colleagues some idea of the long term visions of the space cadets. Gill commented on the heavy overheads that a full system of automatic programming would involve. A. S. Douglas, after listening carefully to what I had to say, made the comment: “But this is extreme Glennie-ism”. It was shortly after this time that J. W. Backus made his famous proposal that led IBM to set in motion the FORTRAN project. I first heard the word FORTRAN over the transatlantic telephone when Arthur Samuel called me from Poughkeepsie about possible IBM of­ ferings for a conference then being planned by the IEE in London for April 1956. He had to repeat it and say it stood for “formula trans­ lation”. FORTRAN allowed the user to write bracketed algebraic expressions, which Glennie’s Autocode did not. Fortran, Glennie’s Autocode, and contemporary systems were the products of experienced programmers who thought of programming from the point of view of the computer itself. When they wrote Fortran statements, many of the early Fortran users had a clear idea of the kind of code that would be compiled, and it came naturally to them to do their debugging with the aid of memory dumps. They would even make patches to the binary program in order to avoid recom­ pilation, which could be a time-consuming business. By contrast, the ALGOL movement included, from the beginning, people who were not at all interested in programming or in the way that computers worked. They took the lordly line that a language should enable a user to say what he wanted in a rigorous and elegant manner, and that the details of the way in which the computer would eventually produce the results was the implementer’s business, not theirs. They turned an uncompromisingly deaf ear to any suggestion that this or that language construct would lead to run-time inefficiency. ALGOL 58 and ALGOL 60 were products of international collab­ oration. I had the chance to take part in both of these endeavours, but, partly because I was preoccupied with other things and partly because I did not properly appreciate the importance of what was going on, I failed to do so. Naturally, I have since much regretted this.

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In 1960 I attended a conference on data transmission organized by the Benelux Branch of the Institute of Radio Engineers and held in Delft. This was something of an event, since up to that time computers used in business and science were essentially free-standing and it was very unusual for them to be connected by telephone lines. The con­ ference was attended by both computer people and by telephone transmission engineers. I was so excited by what I heard that on my return I volunteered to give a lecture to the British Computer Society under the title “Data Transmission and the new Outlook for the Com­ puter Field”. Data transmission clearly added another dimension to the field but at that time no-one could see clearly how things would work out. It was only with the development of multi-programming and time-sharing, together with specifically computer-oriented com­ munication techniques such as packet switching, that the future began to reveal itself. An important consequence of these developments in data transmission, together with parallel developments in telephone switching, was that the two disciplines of computer engineering and communication engineering, which had up to that time been quite separate, began to show a wide area of overlap. The use of redundancy for the detection and correction of errors is an old technique, but a full realization of its power did not come until the mid-1960s or even later. At the conference in Delft, fears were expressed that the errors observed to occur on even the best telephone lines would prove a serious obstacle to their successful use for data transmission, and the transmission engineers present tended to see it as their future task to provide circuits with very low error rates. That this was a misreading of the situation became clear as soon as an improved understanding had been gained of how error control techniques could be applied at the application level to neutralize transmission errors, and it was realized that the ultimate responsibility for error control rested with the user or, perhaps one should say, with the application program. Error control at lower levels is only useful if it increases the effective transmission rate or makes maintenance easier. Experience has shown that even quite noisy lines can be used successfully for data transmission. Once the above points had been grasped, the next step was the development of contention systems in which errors are deliberately allowed to occur, a sufficiently powerful system of error control being relied on to ensure the end-to-end accuracy of transmission. The advantages gained may be the better use of the channel when the traffic is of a bursty nature —as computer traffic usually is —or reduced vulnerability to interference. In the computer field, the pioneering

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application of this technique was in the ALOHA system demonstrated in Hawaii by N. Abramson. Error control techniques depending on redundancy have also been critical to the development of memory systems. Indeed, without them the astonishing progress that has been made in high density magnedc recording would not have been possible. I regard the development of error control techniques and the attitude to errors that goes with them as being every bit as significant as the discovery of the stored program principle. The development of computer networks underwent a major ac­ celeration when the Advanced Research Projects Agency of the US Department of Defense resolved to mobilize the resources available to it and establish the ARPAnet. This imaginative and completely successful project was executed under the direction of L. G. Roberts and was planned from the beginning on the grand scale. It was based on a network of computers that had no other role than switching, it used landlines with a bandwidth of 50 kilobits a second, and it used packet switching, then a technique untried on any large scale. In all these respects it broke new ground, and had an incalculable influence on both the computer and the telecommunication industries. Progress that might otherwise have taken many years was crammed into a few years. Among other good things the ARPAnet included an electronic mail facility. I do not think that this feature originally loomed at all large in the minds of Roberts and his colleagues, but experience of its use has convinced many people that electronic mail is destined to become a major means of communication in the future. Apart from seeing the birth of ALGOL 60 and the beginnings of data transmission, the early 1960s were seminal years in the devel­ opment of computers. They followed a period in which vacuum tubes were giving place to transistors while at the same time the transistors themselves were undergoing rapid development. Computer designers had to do the best they could while the very foundations of their technology were changing under their feet. By the early 1960s, they had successfully emerged from this difficult period, and both they and their customers were reaping the benefit. The new computers were faster than their predecessors and had greater capacity; they were also more reliable. They could now support not only high level lan­ guages but also operating systems. Early batch processing operating systems were more popular with computer service managers than with programmers. Nowadays the term “batch” is used to refer to the queuing of jobs to be run noninteractively. Originally it referred to systems in which all jobs were run through the computer in large batches, so that a user had to wait

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the same length of time for his results whether he was running a program test or a production job. If he were lucky, he would get three sets of results during the course of a working day, although two was more usual. This state of affairs was the source of much frustration among programmers, and the development of time-sharing was a reaction against it. It sought to put the user back where he was in primitive days when he could expect to have hands-on use of the computer. It was in connection with time-sharing that I was to renew my contacts with MIT, which had fallen away in consequence of Charlie Adams leaving MIT and the activity associated with the Whirlwind Computer being transferred to the Lincoln Laboratory, where it became more strictly oriented towards air defence. In January 1963, after a lecture that I chanced to be giving at the Harvard Computation Lab­ oratory, I was approached by F. Corbato with the suggestion that I might like to spend some time at MIT working on a new project— to be known as Project MAC —that they were about to set up. I had met Corbato about a year before in Munich when I chaired a panel discussion on multiprogramming at the first conference of the Inter­ national Federation for Information Processing. That was in June 1962. I had asked Corbato to join the panel at the suggestion of Professor Morse, who was then in charge of the central computing service at MIT. Frank Sumner, of Manchester University, was also a member of the panel. Frank had been working on the operating system for the Atlas computer, which was designed to provide a batch processing service —in the newer sense mentioned above—whereas Corbato was working on an early version of the Compatible Time-Sharing System (CTSS). I was surprised to find how much Sumner and Corbato had in common in spite of the different functions of the operating systems on which they were working. I was able to make arrangements to go to MIT during the summer of 1963 when a Summer Study was being held to inaugurate the new project. This was one of the most thrilling experiences of my life. At the beginning of the period, the CTSS was in the final stages of being checked out on an IBM 7090. Soon we had one or two teletypes connected to the system available to us for a few hours each day. Later we had teletypes in our own offices and the system was available for most of the time. Corbato’s work was based on earlier work at MIT by John McCarthy, J. C. Licklider, and others, and there was another early time-sharing system developed at the System Development Corporation at Santa Monica. However, the CTSS was the first large-scale time-sharing

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system to be offered to a wide and varied group of users. It broke new ground in many respects, and set the pattern for future systems. The CTSS gave me my first experience of interacting with a computer over a long distance. Shortly after my return to England after taking part in the Summer Study, I received a message from MIT suggesting that I should demonstrate the CTSS remotely at a computer conference that was to be held in Edinburgh at the beginning of 1964. The transmission medium would be Telex, this being before the use of modems and the telephone system had become the accepted means of effecting computer communication. Needless to say, the proposal aroused much enthusiam which I shared. However, as the one who would have to implement it, I felt more than a little apprehension, since nothing on this scale had been attempted before. As a first step, I made arrangements to use the telex equipment at the local Post Office. I took with me one of my colleagues who had volunteered to be trained as an operator. Loggingin to the CTSS was like meeting an old friend whom one had not seen for some time and who began at once to chatter away as though nothing had happened. Careful preparation, as usual, paid off and the demonstration was a great success. Later in the year we were asked to give a somewhat similar demonstration to a Medical Research Council symposium held in Oxford. The CTSS had a profound effect on me, and I began to ponder seriously whether we could not do something along the same lines in Cambridge. Fortunately, there did seem a chance, even if a slender one, because as it happened we were engaged on a major constructional project. For some years, EDSAC 2 had been heavily overloaded and much in need of replacement. The obvious thing was for us to try to acquire a Ferranti Atlas computer, which I have just mentioned in connection with its operating system. The design work for this computer—which is famous as being the first computer to have a hardware paging system—had been done at Manchester Uni­ versity under Professor Kilbum. It was the third machine to be designed at Manchester University and developed for production by Ferranti. The University Grants Committee had let it be known that they were willing to receive applications from universities for money to purchase new computers, and we applied for the necessary funds to acquire an Atlas. Unfortunately, they could only let us have £250,000 which, even with an extra £100,000 that the University was prepared to contribute from its own resources, fell far short of what was required. It was not even enough for an IBM 7090 which was our second choice. The other machines available did not seem an adequate advance on

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EDSAC 2. While we were wondering what to do, Peter Hall of Ferranti came up with a suggestion. It was that we should purchase at works cost the principal units of an Atlas computer and should join with Ferranti in designing other units which they would also manufacture and sell to us on similar terms. The result would be a computer which would not have the full power of an Atlas —in particular it would lack the paging hardware—but would be a good deal less costly. This plan appealed to the General Board and was put into effect. My old friend Bill Elliott, who was then at a loose end, agreed to join us as Senior Project Engineer. He was magnificent in that role and it is largely due to his efforts that we carried the project through to a successful conclusion within the original budget. The Titan project—the name was chosen by Peter Hall—involved software as well as hardware. On the software side the major activity was the development of an operating system. This also was part of the collaboration with Ferranti or, rather, with ICT Ltd, a company formed by the merging of a number of computer companies including Ferranti. We had the inestimable advantage of being able to draw on the work that our colleagues at Manchester University and at ICT Ltd had done on the supervisor for the Atlas. Originally the intention was to provide a batch operating system based on the use of magnetic tape for auxiliary storage. This was in an advanced stage of devel­ opment when I returned from MIT in September 1963, but, never­ theless, I began to discuss with my colleagues whether it would be possible to modify the design so as to provide a time-sharing system. At first sight the difficulties seemed formidable. We would have to acquire teletypes and a multiplexer through which they could be connected to the computer. A second base-limit register would have to be fitted and the high-speed memory would need to be enlarged. The major problem, however, was that it would be necessary to acquire and fit a disc file and this would cost £75,000. Our hope was to interest ICT in the project and we felt here that we had something to offer, since time-sharing was a new development of major commercial im­ portance. The negotiations were conducted by Bill Elliott with Basil de Ferranti, then joint managing director of ICT and a good friend of Cambridge. De Ferranti became infected with our enthusiasm and he agreed on behalf of ICT to provide a disc hie on the understanding that ICT should have the use of a proportion of the time available on the system when it was working. With this support we were able to go ahead. I realized that I was asking a lot of my colleagues in suggesting that they should re-align their plans in midstream, but they responded nobly, and the project

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was a great success. The system was not fully interactive in the strict sense, since all the interactive services —such as editing and hie man­ agement—were provided by the operating system and the ordinary user could not himself write interactive programs. However, when he activated a program and it ran to completion, the results would au­ tomatically appear on his terminal. We were surprised to find how successful this was. To the ordinary user, it was to all intents and purposes an interactive system. The multiplexer was based on a design originally proposed by myself and then reworked and improved by David Wheeler. This pattern of collaboration between Wheeler and myself followed the precedent set when the 16 k word core memory was being added to EDSAC 2. The multiplexer could handle up to 64 teletype lines. It contained a small core memory with one word for each line, the word being long enough to hold a single character, together with a number of status bits. During reception, each line was scanned once every 1.2 milliseconds, and the incoming digits used to build up the character in the appropriate word in the memory. When the character was complete and ready for transfer to the computer, the computer was interrupted. Transmission of characters from the computer to a teletype was accomplished in an analogous manner. At times when the multiplexer was disconnected from the computer, it would echo back to the sending teletype all characters received, thus indicating to the user that failure of the computer to respond was not due to a fault on the line. I think we all realized that it would have been in many ways preferable to use a PDP-8, a low-cost minicomputer that had just appeared on the market, but the cost advantage in favour of a purpose-built multiplexer was significant. I had been very apprehensive that we would have as much trouble with the multiplexer as with the rest of the system put together, but in fact it hardly ever went wrong. Later, the Flowers Committee, which had been set up by the gov­ ernment of the day to review the computing facilities available in British universities, included in its report a recommendation to the effect that we should receive a special grant of £100,000, and with it I was able to pay for the disc file. Nevertheless, the debt to Basil de Ferranti and ICT remained a very great one since, without his prompt and farseeing support, the project would never have got off the ground. As it was, it gave the University a time-sharing service operating round the clock six days a week. It ran until October 1973, when the com­ puting load was transferred to an IBM 370/165. By then the name of the laboratory had been changed from Mathematical Laboratory

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to Computer Laboratory, and the computing service reorganised as an autonomous subdepartment under Dr David F. Hartley. The explosive growth of interest in interactive computer graphics also dates from the early 1960s, although its origins, as with so many things, go back to earlier days. Not only did computer graphics present many new and challenging problems to the systems programmer, but it opened up a whole new range of computer applications. One of these was Computer Aided Design, known for short as CAD. My enthusiasm—and that of many other people—was aroused by a de­ scription given at the Spring Joint Computer Conference in 1963 by Ivan Sutherland of a system known as Sketchpad. This he had developed as a Ph.D. project at the Lincoln Laboratory of MIT where much pioneering work in graphics was then being done. I was sufficiently impressed to write a short description of Sketchpad for Control, a London-based journal for control engineers for which I was an editorial consultant. Computer graphics also made possible the computer game, which has since done so much either to enhance or diminish, according to how you look at it, the quality of life. The original computer game was Space War written by a group of young enthusiasts at MIT in 1961. Its serious purpose was to demonstrate how a computer could be programmed to accept and respond to external stimuli. I remember John McCarthy’s showing it to me and remarking wryly that even he was shocked when he found people actually playing Space War as a game instead of using it as a vehicle to study man-machine relations. At about the time these developments were taking place, I was planning, with the support of the Science Research Council, to expand the program of research in Computer Science in the Mathematical Laboratory in order to take advantage of the opportunities offered by the Titan computer. The budget included a sum to be spent at my discretion on capital equipment, and I used it to buy, from the Digital Equipment Corporation, a PDP-7 computer with a type 340 display. This display, which was very advanced for the period, would run autonomously, stealing cycles from the computer to access a display table held in the high-speed memory. The PDP-7 and display were delivered in 1965, and Neil Wiseman designed a data-link to connect it to the Titan computer. This was constructed and installed by lab­ oratory staff. My personal interest was in establishing a program in CAD, but I was keen that the system should be made available to anyone, inside or outside the laboratory, who could make good use of it. One notable external user was William Newman, son of Max Newman whom I

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have already mentioned as being my supervisor in my first term at St John’s College. William was a research student at Imperial College, London and he developed, as his Ph.D. project, an experimental system for helping an architect to design a school, or similar building, using standard modules. This was very original work and William, following a precedent set by Sutherland, made a short him in which its features were demonstrated. Within the laboratory, Neil Wiseman began to work on screen editors, using the PDP-7 with its data-link to the time-sharing system in exactly the way in which low-cost personal computers came to be used very much later. He made use of this experience later when he spent two years on secondment to the Cambridge University Press, developing for them an early and highly successful computer type­ setting system. On various visits to MIT during the period 1963-5,1had met Charles Lang, a young Englishman who was working under D. T. Ross on what was described as CAD, although Ross’s main interest at the time was in a form of ALGOL, known as AED, intended ultimately to form a basis for a CAD system. Charles was looking for an opportunity to return to the UK, and I suggested to him that he might like to lead a CAD group in Cambridge. He accepted my offer, and joined the Mathematical Laboratory in the latter part of 1965, soon after the PDP-7 had been delivered. The first task he undertook was to write the software for the data-link. At first, interest in Lang’s group centred on the design of objects with curved surfaces, such as aircraft noses and automobile bodies. Use was made of cubic surfaces, known as Coons surfaces after Professor Coons of MIT who originated them. To describe a complex surface, it was necessary to put together a number of separate surfaces, referred to as patches, in such a way that the first derivatives were continuous at the joins. Rather surprisingly, only four or five patches were required to describe the nose of an aircraft. This work went very well, and we enjoyed an active collaboration with the British Aircraft Corporation. Unfortunately, the project for which the design was being done was cancelled. Other companies with whom we had contacts were General Motors in Detroit and Renault near Paris. One day, Lang brought back from Renault a model of a curved surface that had been cut in a rigid foam plastic material on a nu­ merically controlled machine tool. I was impressed by the potential value of such models as aids to visualization during the design process, and I conceived the idea of constructing a foam cutting machine that would resemble a machine tool but would be much lighter in con-

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struction and would be designed to cut foam and other soft material at high speed. I felt that if such a device could be made at low cost it might take its place as a computer peripheral and play a role similar to that of an ordinary plotter. We built two experimental foam cutting machines and achieved some considerable success with them, but we lacked the resources necessary to finish the development. I do not think, however, that the end has been heard of this idea. An altogether different branch of CAD —now usually referred to as CAD/CAM, the M standing for manufacturing—is the design of components intended to be manufactured by means of numerically controlled machine tools. Two approaches have been made to this subject. One is to regard drawings as fundamental, as they are when traditional design methods are used, and to develop computer systems that are essentially drafting aids. The other more radical approach is to regard as fundamental a data structure created by the designer in the computer memory. This data structure is in effect a complete model of the object, and all subsequent steps involved in the manu­ facture of the object are based on that model. In particular, both drawings and the data to be fed to numerically controlled machine tools are derived from the model. If this approach could be followed to its logical conclusion, one would expect that drawings would lose their central role in manufacturing and be required only for visualization and documentation. Lang began to work with his students on solid modelling—the term now used to describe the second approach—as early as 1968, but real progress was not made until Ian Braid joined the group. Braid’s thesis entitled “Designing with Volumes” appeared in 1972, and was a land­ mark in the development of solid modelling. Essentially the idea was to form complex objects by combining a number of primitive solids with positive or negative volumes. Braid constructed an experimental system based on these ideas, to which he gave the name BUILD. In the course of the work he switched from the low level programming language he had been using to ALGOL 68 and as an observer of the scene I was struck by the manner in which he then began to forge ahead with increased confidence. I feel that those who have persisted in using unsuitable languages such as FORTRAN for complex tasks in symbol manipulation—which is what solid modelling involves—in the expectation that this will make their work more acceptable have misjudged the situation. No engineer would use a blunt tool when he could get a sharp one; why should he use a blunt programming lan­ guage when sharp ones are available? This is not to say that FORTRAN is not a perfecdy acceptable choice for general engineering calculations.

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Early demonstrations, such as Sketchpad, were very successful and were of great value in gaining support for research in CAD. In a sense, it can be said that they were too successful, since by their strong visual appeal they tended to give people the idea that the subject was further advanced than it was. Those who were working in it realized that a long pull lay ahead. It has taken 20 years for CAD/CAM systems that are something more than simple drafting systems to gain a foothold in industry and even now solid modelling systems are only just be­ ginning to receive attention. I would expect solid modelling gradually to come into its own as companies begin to rely more and more on computer methods for manufacturing as well as design. The CAD group in Cambridge flourished for 15 years, a long time for sustained effort in a university department. When it was wound up on my retirement as head of department, Braid was in charge. Lang had left some years earlier and had founded a small company to work on CAD/CAM. Braid now joined him in this enterprise. Neil Wiseman had earlier been responsible for some pioneering work on the computer aided design of computer circuits and their layout. This is a very different subject from the mechanical CAD that I have just been describing. Neil’s work was quite promising, but integrated circuits were then in a state of rapid development and he found it difficult, in an academic environment, to keep up with the advances that were being made. Looking back, I very much wish that I had encouraged him to persevere. During the late 1950s and early 1960s, I had watched with consid­ erable interest progress in the use of computers for algebraic as distinct from numerical calculation, and had felt attracted to the subject as one to which I might possibly make some personal contribution. I therefore stressed algebraic manipulation when I came to make my proposals to the Science Research Council for the expanded program of computer science research that I referred to above. It had been my idea that a language of the pattern matching, or Markov algorithm, type would be highly suitable for computer algebra but, after exper­ imenting with one such language, I became disillusioned. At this point, I discovered that David Barton, a young research worker in the lab­ oratory, was also interested in computer algebra. I decided, therefore, that I would support his research instead of pursuing the subject myself. When, in due course, Barton left the Laboratory, his group was taken over by John Litch, who in turn was succeeded by Arthur Norman. The algebra group was always smaller than the CAD group, but was active over a similar period.

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When the ARPAnet was extended to England, Barton was able to use it to establish contact with groups in Salt Lake City and at MIT under Tony Heam and Joel Moses, respectively. The use of the AR­ PAnet remained central to the work of the Cambridge group, and as time went on Fitch and Norman developed a close collaboration with Heam. It was of the greatest utility to be able to use other systems on a day to day basis, and to be able to compare their performance with that of the local system on the same problem. This not only led to a close scrutiny being made of the competing systems to make sure that the algorithms on which they were based were correctly imple­ mented, but it led to a deeper understanding of the relative merits of this or that algorithm or data structure in differing circumstances. A series of notes appeared in the Bulletin of the ACM Special Interest Group for Symbol Manipulation in which the performance of the several systems on practical problems was compared. I contributed one or two problems which I had encountered in the course of my research; one was the computation of the variance of terms generated by a recurrence relation in the presence of noise. I would like to end this chapter by saying something about the planning of university research projects. Such projects may be motivated in a number of ways. For example, they may be thought of primarily in connection with the training of graduate students or they may be the result of a desire on the part of a faculty member to follow up his particular interests. My aim has always been to originate projects which, whatever their immediate motivation, will ultimately be seen as lying in the main stream of computer progress, that is, as contributing to the development of the field as a whole. Such projects are inevitably of a long-term nature, and it typically takes ten years or more for the resulting innovadons to be generally accepted in the computer industry. Examples are micro-programming and hardware paging. Because of this long gestadon period, industrial managers do not always appreciate where the original ideas came from. While collaboration between industry and people in universides on short-term projects can, given favourable circumstances, be advantageous, it is in my opinion through long-term research that universities can make their most valuable contribution. A project may be described as being in the main stream if, when it matures, the results obtained are of current topical interest and lead either to further research or to practical exploitation. In order to assess whether or not a suggested project falls into this category, it is necessary to look into the future. There are two questions that one can and should ask about the future. One is: “What is going to happen?” This

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will lead to projections based on current developments. The other question is: “What will the future be like?” In particular, what will be the technological, economic, and sociological forces that will mould it? In order to assess a proposed long-term research project, or for that matter any long-term project, one thus needs a view or a model of the future. A project can fail for various reasons. It can fail because it is based on a faulty model of the future. It can fail because it is based on ideas which turn out to be technologically unsound, that is, to be in some unforeseen way in conflict with the laws of physics. Finally, it can fail for management reasons; that is, because either the team or the leadership is inadequate for the task. I will give examples of projects which have failed for one or other of these reasons. In 1961, the fastest (germanium) transistors available had a cut-off frequency of about 600 megahertz, but even this performance could be obtained only by selection. On the other hand tunnel diodes—so called because their operadon depended on the quantum mechanical tunnelling effect—with a cut-off frequency of 3000 megahertz were available. A diode, being a two-terminal device, is not an easy com­ ponent with which to build a computer, but nevertheless by making use of a multi-phase clock this can be done.* It was about this time that N. E. Wiseman, whom I have mentioned several times above, joined us as Chief Engineer. Wiseman had worked for the Mathematical Laboratory in the vacation while still a student at Queen Mary College, London. He had then spent two years at the University of Illinois and on return to the United Kingdom had taken a post at the Elliott Brothers’ Research Laboratories at Boreham Wood. When he joined the Mathematical Laboratory, he brought with him experience of tunnel diodes and he soon succeeded in demonstrating a circular shift register containing 2000 tunnel diodes and capable of operating at 250 megahertz. This seemed a very promising line of development, and I had no difficulty in obtaining a grant from the Science Research Council to finance a full-scale research project. It was of course realized that transistors would get faster, but the argument was that tunnel diodes, being much simpler than transistors, would always be faster still. This model of the future was entirely false. The development of planar transistors made phenomenally rapid progress, while tunnel diodes proved difficult to make. Naturally the semi*This had been demonstrated in Japan by E. Goto who was responsible for the design of a successful computer based on the use of the parametron, also a twoterminal device. At one time it looked as though there might be a future for parametrons working on very much higher frequencies than Goto had used, but the tunnel diode, the use of which Goto also pioneered, appeared more attractive.

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conductor industry followed up its success, and tunnel diodes became hard to obtain. The project therefore failed, not for any intrinsic reason and certainly not because of the quality of the effort that Wiseman devoted to it, but because the semi-conductor industry developed in a way different from that expected. The failure of the tunnel diode project was a great disappointment, since following the success of EDSAC 2 the Nuffield Foundation had made a further large grant to the Laboratory, and had agreed that this might be used to construct a superspeed research computer based on tunnel diodes. The bulk of the money received under this grant had to be returned to the Foundation. A few years earlier we had done some preliminary work on a project which, had it gone ahead, would have failed because it was based on an unsound idea. The success of the core memory in the mid 1950s led people to suggest that the non-linear properties of ferrite cores would enable them to be used for logic as well as for storage. The idea was that the processor proper would be constructed from cores and copper wire. It would be entirely inert, but would be brought to life by being driven from a power supply unit that provided a variety of square waveforms, each having a different mark-space ratio. These would all be of a strictly repetitive character. For this reason, although the power supply would contain vacuum tubes, it would be easy to maintain and could be expected to be very reliable. Since there would be little that could go wrong in the processor itself, the result would be a highly reliable computer and, of course reliability was at the time a much-needed quality. It was not difficult to demonstrate short shift registers, adder chains, etc., working on the above principles. However, when an attempt was made to build larger units, it was found that the operation became marginal, and it was necessary to introduce diodes to provide additional nonlinearity and transistors to provide gain. As someone remarked, when this had been done one might as well throw away the cores and use only the transistors and diodes in a more conventional manner. These facts were, however, not appreciated to begin with, and on the basis of some early and encouraging experiments, we wrote a proposal for a project and obtained a promise of financial support. However, we withdrew in time. Other people burnt their fingers over similar projects. When the Titan project was launched we had to consider what high level languages we would provide to go with our shiny new computer. The idea that languages should be independent of machines had been given a strong impetus by the ALGOL movement and by FORTRAN,

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which had originally been developed by IBM for the 704 and was rapidly becoming an industry-wide language. It was clear that FOR­ TRAN would be required for the Titan, and equally clear that the Cambridge Autocode, which had been written by David Hartley for EDSAC 2 and which had proved a great success, would also be required. We were anxious to provide some more modem language as well. In retrospect, it is clear that we should have provided ALGOL 60. How­ ever, while recognizing that the development of this language was an important advance, I was ambivalent about it as a language for serious computation. The original developers of FORTRAN put a strong em­ phasis on run-time efficiency, and indeed it was necessary for them to do so to obtain a hearing at all in a world accustomed to programs expertly coded in assembly language. It was in fact to be many years before the standard of optimization set by the early FORTRAN com­ pilers was exceeded. The designers of ALGOL 60 had reacted against this emphasis on run-time efficiency and some of them appeared to go out of their way to give the impression that they did not consider it to be of any importance at all. My colleagues felt much as I did on these issues and accordingly we decided to try our hand at defining and implementing a new language to be based on ALGOL 60 but free from the defects of that language as we saw them. The name chosen for the new language was CPL which originally stood for Cambridge Programming Language but which later, when a group at London University joined in the project, was re-interpreted to mean Combined Programming Language. This project was a complete failure. The original goal of producing a language suitable for practical use was lost sight of and the project became one of research into language design and implementation. I felt much mortification over the failure of the CPL project, and my feeling of failure was accentuated when some years later, during a visit to Stanford University, I had experience of ALGOL W, a language designed by Niklaus Wirth. This I perceived to be exactly the kind of development of ALGOL 60 that I was hoping for as a result of the CPL project. However, I began to look at the matter very differently when I read Tony Hoare’s Turing Lecture delivered in 1980. Hoare described a computer language project he had been associated with at Elliott Brothers Ltd at about the same time as we were struggling with CPL. Although on a larger scale, this project ran into very similar difficulties and eventually had to be abandoned. Other contempora­ neous software projects also ran into grave difficulties, although in some cases the difficulties were eventually surmounted. The fact was that we were all over-ambitious and wholly lacking in experience of

226

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large software projects. We did not appreciate how many and how seductive were the opportunities for escalation, and having no insight into the dangers could establish no defences. The fundamental causes of the failure of the CPL project were those I have just indicated. However the immediate cause was my appoint­ ment to the staff of Christopher Strachey. At the time that the Manch­ ester Mark I computer was coming into action, Strachey was earning his living as a schoolmaster. Through a slight acquaintanceship with Turing he had an opportunity to try his hand at programming for it and his abilities as a programmer soon became apparent. He was fortunate enough to attract the attention of Lord Halsbury, then head of the National Research and Development Corporation, a British Government agency charged with providing finance for promising technological projects, and he joined the staff of the Corporation. One of the projects being supported was the development of the Ferranti Pegasus computer. As representative of the Corporation, Strachey exerted a strong influence on the design of this computer, of which a number were in due course made and sold. At the time I invited him to come to Cambridge he was practising as a private consultant in London. He and I shared a number of views on the subject of ALGOL 60 and we had collaborated in a paper that was published in the Communications of the Association for Computing Machinery. I liked Strachey personally, but I realized that he was not an easy man to work with, and that I was taking a chance in employing him. He was rather overbearing in technical discussions and apt to insist on minor points with the same force that he insisted on major ones. For example, he did not like the use of the ALGOL word “else,” which he said was ungrammatical, and he insisted that in our paper we should use “otherwise.” I protested that there were more important issues to raise than that one, but he was adamant. Coming to Cambridge had greatly improved Strachey’s academic standing and he would have liked to stay there and lead a group to work on language theory. Halsbury, who was then Chairman of the relevant committee of the Science Research Council, was anxious to provide financial backing. Strachey, however, wanted much more free­ dom than he could have had within the Cambridge University frame­ work as it then existed, and in the end he set up a group in Oxford. It was there that he finally got his act together. He met Dana Scott, and their work began to attract attention. It was too theoretical for me to assess and I found that none of my more mathematical friends would commit themselves as to its value. In fact, it was not until after Strachey’s sudden and tragic death in 1975, as a result of a liver

Computer progress 1 9 5 5 -8 0

227

infection, that the work he had done with Scott achieved general recognition. A research project that came to fruition at a time when the subject was one of topical industrial interest, was concerned with hardware support for memory protection. The origin of this project is interesting, and illustrates how chance contacts made in the course of travel can have important consequences. In June 1967, I was invited to attend a meeting on Long Island, New York, called to discuss computer science education. There I met Victor Yngve of the University of Chicago whom I knew as the originator of the COMIT programming language and as an authority on the use of computers for the syntactic analysis of the English language. To my surprise he told me that he was concerned in a hardware project, and on my expressing interest invited me to visit Chicago on my next trip to the United States. I did so in August. When I got there, I met Bob Fabry who was working as a graduate student under Yngve. Together they were designing a processor in which access to memory would be strictly controlled by the loading into special registers of words called “capabilities.” The hardware was such that capabilities could not be forged or modified in the accumulator. The term capability was originally introduced in a software context by E. C . Van Horn of MIT, but this was the first time that it had been used in the context of hardware design. I formed the view that the work of Yngve and Fabry was more highly original than they realized, and I went back to Chicago in June the following year for a more extended visit. I included a section on hardware capabilities in a book on time­ sharing which I was writing at about that time, and which came out in 1968. Perhaps because of difficulties on the constructional side— the project was in the end abandoned—Yngve and Fabry had published nothing, except for a short note inserted at my suggestion into the quarterly report of their Institute. One thus had the highly unusual situation of original work being published for the first time in a book rather than in a journal. This may have led some people to think that the use of hardware supported capabilities was a well-established tech­ nique instead of being still an experimental idea. My contacts with the Chicago group came at a time when vigorous discussion was going on in my own laboratory, in particular between Roger Needham and myself, as to what our next large research project should be. Everyone was saying at that time that it would not be long before very low cost microprocessors would be available, and that a large number of these, suitably interconnected, might form the main frame of the future. We gave much thought to possible projects based

22 8

Memoirs o f a Computer Pioneer

on this idea, but in the end concluded that all of them were open to objection. If a small number of memory modules were used, then the available memory bandwidth would not enable more than two or three processors to be supported. If, on the other hand, a large number of memory modules were used, then the cost of the necessary crossbar switch and its slow speed of operation would prove serious disadvan­ tages. Systems in which each processor had access only to part of the memory did not appeal to us at all. In view of these considerations, we decided not to establish a multi-microprocessor project. In consequence of the above decision—which we have since had no reason to regret—we were free to embark on a project based on the Chicago ideas. This became known as the Cambridge CAP Com­ puter project and was led by Roger Needham. In all it occupied ten years, starting in 1970. After a lengthy preliminary study, a mini­ computer with capability hardware was designed and implemented using the relatively primitive TTL semi-conductor parts of the period. The implementadon was a major undertaking and was the responsibility of David Wheeler. The next task was to design and commission an operating system which exploited the capability features. After that the computer was put into operation to serve a small but genuine group of users. Finally came the writing of a book describing the work that had been done. The Cambridge CAP Computer was not in fact the first computer built which supported capabilities in hardware. I had been invited to act as a consultant to Plessey Telecommunications Ltd, who were interested in the design of a computer for controlling the switch of a telephone exchange. Their first proposal was for a computer with no form of memory protection. I pointed out the disadvantages of this in a situation in which ruggedness and rapid indication of faults were important, and I gave Jack Cotton, the engineer in charge of the project, a copy of the draft of the book on time-sharing that I referred to above. He saw in hardware supported capabilities the solution to his problem, and so the Plessey System 250 came into being. Another project, which illustrates in a somewhat similar way the importance of casual contacts in stimulating research, was the devel­ opment of the Cambridge digital communication ring. Not only was this very successful in its own right, but it had an enlivening and unifying effect on the research of the department. By September 1980, when I retired from the department, between forty and fifty computers and other devices were connected to the ring and it was supporting, among other things, a major project in distributed computing.

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In January 1974, as part of a lecture tour of Switzerland undertaken on behalf of the British Council, I had spoken at the Hasler Company in Berne. They showed me a digital ring operating at a pulse rate of 10 megabits a second. The application demonstrated was digital te­ lephony, but it was immediately clear that the same technology could be used for other purposes, in pardcular for interconnecting computers. The design study for the Cambridge ring was published in 1975. The project had several objectives, all of which were achieved. In the first place we set out to show that the use of technology familiar in the computer world would enable numbers of computers, located within a strictly local area, to be interconnected, with a much higher data rate and at a much lower error rate, than was possible using traditional telecommunication techniques. It was obvious to us that, with the increasing number of computers to be found everywhere, a need would be felt for a system of interconnection with these properties, if only in order to enable resources to be shared. Shortly after we had published our design study, the Ethernet was announced and we were glad to know that others were thinking along similar lines, although the technical means they employed were quite different. A second objective was to demonstrate that reliability would not be a problem. A ring is, of course, highly vunerable, since the failure of a single repeater is sufficient to put the whole system out of action. It was this consideration that had put an effective brake on ring de­ velopments in the days before integrated circuits were available. We felt that their coming had changed the picture. A final objective was to demonstrate that a ring could be built without incurring great cost. Development work on the Cambridge ring began soon after the design study was published and the ring began to come into use in the later part of 197 7. It immediately became apparent that any fears that the reliability of the repeaters would prove inadequate were groundless. When, in the summer of 1980, I was nearing the age at which the ordinances of Cambridge University require that a professor shall lay down his office, Nina and I decided that we would both like to live and work for a time in the United States. Our children were now grown up and we had no other family responsibilities, so that we were free to go. We are now living in Maynard, Massachusetts, an oldfashioned New England mill town that Digital Equipment Corporation rescued from decay, when the mill finally closed, by buying the build­ ings and converting them for use as its headquarters. They did me a similar service by taking me on their payroll.

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I had long wanted to see something of the computer industry from the inside and the present period is an interesting one in which to do so. Powerful computers of all sizes are becoming widely available, and computer applications that were until recently of academic interest only are coming into everyday use. Expert systems form one example. The demand for still higher speeds is making processor design more exacting and formal methods, once the plaything of the theoretician, are becoming part of the stock-in-trade of the pracdcal design engineer; as a result, the work bench and the oscilloscope are giving place as design tools to the terminal and the simulator. The computer industry has become dependent on its own products for its further advance.

Sources a n d acknowledgements

British Government documents relating to the second world war were deposited in the Public Record Office, London in 1969. These included hies that I had worked with during my war service. I was able to use them to fill in gaps in my memory and to check facts and dates. The documents on which I principally drew are indexed under AVIA 7, 10, 22, and 26 and under WO 32, 195, and 199. WO 32 11625 contains proofs of a “History of Army Radar” by Brigadier A. P. Sayer. This was printed shordy after the war, but classified as restricted and not published. I am informed by Mr. I. C. Graham, Senior Librarian of the Royal Signals and Radar Establishment, that copies have now been deposited in the British Library and in the Library of Congress. Lady Cockroft kindly allowed me access to papers left by Sir John Cockcroft and preserved in the Churchill College Archive. Dr Boot let me see notebooks and papers relating to the early development of the cavity magnetron; these have been since deposited in the library of the Institution of Electrical Engineers in London. Many of the former colleagues whose names appear in the text have shared recollections with me. Otherwise, apart from published sources, I have drawn largely on personal travel diaries and on Cambridge University records, in­ cluding Computer Laboratory records. Among published material about the war period, I found the fol­ lowing of particular value: S. W. Roskill “The War at Sea” HMSO London (official history) C. H. Waddington “Operational Research in World War 2” Elek Sci­ ence, London. 1973 P. M. S. Blackett Brassey’s Annual 1953 page 88

232

Sources and acknowledgements

I am grateful to the following by whose courtesy the photographs indicated are reproduced: Imperial War Museum, London, (11, 12, 13) Computer Laboratory, Cambridge, (15, 16, 17, 18, 20, 25) Dr Joseph Weizembaum, (21) Science Museum, London, (24) Moore School of Electrical Engineering, (26)

Index

AA Command radio school, 65-6, 69 AA Command, introduction to, 66 Abramson, N., 213 ACE, 136-8, 146, 173 Adams, C. W., 176-7, 180, 181, 182, 210, 214 ADEE, 36, 45-8, 52, 54-63 Admiralty Computing Service, 109, 169 Admiralty Signal Establishment, 72, 127, 129 ADRDE (ORG), 69-70, 78 ADRDE, 62, 66, 69, 75, 78, 131, 135 Advanced Research Projects Agency, 213 Agricultural Research Council, 204-7 Aiken, Howard, 122, 124, 128-9, 170, 174-6 Air Defence Experimental Establishment, see ADEE Air Defence Research and Development Establishment, see ADRDE Airy’s integral, 145, 148 Alexander, S. N., 161, 168-9 ALGOL, 211, 220, 224, 225, 226 Allen, Dr, 102 ALOHA, 213 Alt, F. L„ 169 Amateur radio, 5-6, 7-8, 15-16 American radar equipment, introduction of, 84-5 Amundsen, R., 114 Anomalous propagation, 73-4 AORG, 78 Appleton, E. V., 17, 24, 33, 56, 74, 111-2

Army Operational Research Group, AORG

see

ARPAnet, 213, 222 Art Institute (Chicago), 170-1 Art Museum (Vienna), 173 Ashmead, J., 43, 45, 51, 52 Association for Computing Machinery, 170, 177, 180-1, 202, 210 ASV, 86-8 Atlas Computer, 214, 215 Atmospheric oscillations, 112-5, 141 Auerbach, I. L., 202-3 Austria, 96, 100 Automatic programming, 209 Automatic Sequence Controlled Calculator, 107, 124, 128, 160, 168, 174 Aves, R., 40 Babbage, B. Herschel, 200 Babbage, Charles, 197-200 Babbage, Dugald B., 200 Babbage, Henry P., 197, 200 Backus, J. W., 211 Baker, H. F., 14 Bartels, Julius, 156, 158 Bartlett, F. C., 23, 52 Barton, David, 221 Barton, S. A., 129 Bawdsey Research Station, 35-7, 43, 44 Bayliss, L. E., 66, 70, 72 Bedford attachment, 64 Bedford, L. H., 64 Bell Relay Computer, 170 Bembridge fort, 59 Bendix Corporation, 173 Bennett, A. J., 9 Bennett, H. H. G., 133 Bennett, J. M„ 140, 171, 192, 210

234

Index

Benson, John, 59, 79 Berkner, L. V., 122 Best, J. E., 20, 22 Bigelow, Julian, 163-4, 171, 185 Biggin Hill, 35, 38, 45, 102 Bjerknes, V. F. K., 114 Black, D. H., 54, 56 Blackett, P. M. S., 64, 66 Bladder, Joyce, 188 Bletchley, 88, 135, 137 Blumlein, A. D., 68 Bomber Command, 87 Booker, H. G., 20 Boot, H. A. H., 56 Booth, A. D., 139 Booth, G. C., 133 Boothwick, Captain, 97 Bowden, B. V., 40 Bowman, J. R., 175 Boys, S. F„ 152 Boyt, J. E„ 9 Bragg, W. L„ 103 Braid, Ian, 220-1 Brainerd, John, 14 Bratt, J. B„ 25, 26 British Association for the Advancement of Science, 33, 105 British Computer Society, 192, 198, 200-2, 203, 204, 212 Bridsh Conference on Automation and Computation, 201 British Tabulating Machine Company, 140-1 Brookes, Alexis, 179 Brown, Joe, 2, 6, 12 Bruneval raid, 76, 78 Brunt, Sir David, 201 Buchner, Dr, 155-6 Burks, Arthur, 163, 165 Burroughs Corporation, 181 Bush, Vannevar, 27, 123, 124, 155 Butement, W. S., 37, 43, 45, 55 Buxton, H. W., 199 CA No. 1 Mark I, 74 CAEE, 58-62, 76, 77, 78, 79, 144 Caldwell, S. H., 122, 124 Cambridge ring, 228-9 Cambridge University Press, 219 CAP computer, 228 Capability, 227-8 Carpenter, H. E., 12 Carr, John, 177, 210 Carter, C. J., 90, 97

Carter, N., 59 Cathode ray tube memory, 122, 134-5, 164, 176, 181 Cavendish Laboratory, 18, 20-2, 34, 35, 44, 50, 52, 55 CD equipment experimental, 37, 43, 46 basis for CDU and CHL, 43-4 trials, 61-2, 70, 78 CD/CHL chain, 62, 72-3, 82 CDU stations, 44-50, 52 Centimetric radar, early development of, 55-6 Chain Stations, 35-8, 44 Bawdsey, 36, 43 Dover, 41 Dunkirk (Canterbury), 38, 40-3, 60, 118, 186 Ventnor, 56, 60, 73 Chamberlain, Neville, 33, 41, 57 Chapman, Sydney, 17, 26, 113, 141, 156 Chamwood, Lord, 59 Checkers, 197 Chick, D. R„ 70 CHL equipment origins, 43 chain, 46, 50-2 Ingoldmels, 52-3 Shotton, 50-1 Christchurch, move of ADEE to, 45, 54 Churchill, Winston, 57, 58 Claughton, Sir Gilbert, 2 Clippinger, R. M., 170 Coast and Anti-Aircraft Defence Experimental Establishment, see CAEE Coast artillery in action, 74-6 radar for, 37, 61-2, 70, 74 Coast watching, 61, 72-4 Coastal Command, 66, 84-8, 89 Cockcroft, J. D., 24, 34, 43-5, 47-53, 57, 62-3, 64, 66, 68, 70, 73-4, 78, 79, 80 Cocking, W. T., 5 Colebrook, F. M., 6, 138 Colloquia, 140, 144, 210 Colossus, 135, 137-8 Compatible time sharing system, 214-5 Compton, S. C., 12 Computer Aided Design, 218-21 Computer algebra, 152, 221 Computer graphics, 218-21

Index

Computer Laboratory, 218 Comrie, L. J., 105-6, 108, 109, 156 Conference in Cambridge (1949), 144-5 Coombs, A. W. M., 135 Coons, Professor, 219 Cooper, Duff, 34 Cooper, R. 1, B., 80 Corbato, F., 214 Core memory, 181-3, 185-7, 209 Comer, J., 102 Costelloe, W. H.J., 47 Cotton, Jack, 228 CPL, 225-6 Craik, K.J. W., 22-3, 52 Croquet, 23-4 Cryptanalysis, 88, 135, 137-8 CTSS, see Compatible time-sharing system Culver fort, 58-60 Cunningham, Ebenezer, 11, 13, 16, 17 Curtis, J. H., 169 Dahlgren, Naval Proving Ground, 165, 170 Darwin, C. G., 29, 135 Data transmission, 212-3 Debugging, 145 Decca Radar, 190 Dee, P. I., 35 Diamond, Jack, 22 Dieminger, W., 99, 100, 158 Differential analyser, 25-8, 29-30, 33, 107, 123, 124, 154-6, 169-70 Digital Equipment Corporation, 218, 229 Distributed computing, 228 Doenitz, Admiral, 85, 88 Douglas, A. S., 172, 179, 21 1 Dover, coast artillery at, 74-6 Draughts, 197 Druller, I. D., 3 Dudley, Earl of, 2 Dundee, move of TRE to, 43 Dykes, Paul, 59 DYSEAC, 169 Eastwood, W. S., 70 Eckersley, T. L., 32-3, 60 Eckert, Presper, 108-9, 120, 121, 123, 139, 160, 166-7, 183 Eckert-Mauchly Corporation, 165, 166, 167 Eddington, Sir Arthur, 16-17

231

EDSAC 1.5, 188 EDSAC 2, 184-94, 195, 215, 216, 217, 224, 225 EDSAC origin of, 122 building of, 127-42 programming for, 143-53 early applications of, 148-9, 152-3, 191-3 film of, 179 closing down of, 188-9 EDVAC, 108-9, 120-1, 123, 127, 168 Electronic brains, 195 Elliott Brothers, 191, 223, 225 Elliott, W. S., 16, 38, 40, 216 Elsie, 70-1 EMI Ltd, 68 ENIAC, 107, 108, 109, 117, 119-20, 122, 132, 160, 169, 195, 197 Evans, Col. C. H. Sylvester, 63 Evans, G. C., 47, 49, 50 Everett, R. R., 176 Exhibitions, British Empire, 32 Fabry, R., 227 Falloon, S. W. H. W., 20, 33 Farley, F. J. M., 75 Farmer, F. T., 20, 33 Farmer, P. F., 105, 129 Father, 1-3, 11 Feather, N., 35, 36 Ferranti, Basil de, 216, 217 Ferranti Ltd, 215, 216 Ferranti Mark 1, 179, 187, 209 Ferrard, C. L., 59 Fertel, G. E. F., 36, 47, 49 Fighter Command, 35, 37-8, 83-5, 85-8 Finney, D. J., 206 Fisher, R. A., 148, 204 Fitch, John, 221-2 Fleming, Sir Ambrose, 6 Floating address, 180, 193 Flowers Committee, 217 Floyd, R. W., 145 Forrester, J. W., 176, 181 Forshaw, H. W., 54-5, 62 FORTRAN, 211, 220, 224-5 Fowler, R. H., 18 Francis, W. L., 83 Fraunhofer Institute, 158 Freeman, H., 204 Fremantle, Lt-Col. the Hon. J. W., 66 French, Johnnie, 95

236

Index

G15, 173 Gamma function (complex), 147 Gant, T. H. T„ 40 Germany, impressions of, 91-2, 93-4, 97-8, 156-9 Gill, S., 146, 149, 172, 180, 203, 210,

Huskey, H. D„ 138-9, 168, 173, 189 Huxley, L. G. H., 83

IBM, 141, 167, 168, 175, 183, 211 ICT, Ltd, 216, 217 IFIP, 200, 203-4, 214 211 ILLIAC, 171-2 Ingham, A. E., 11 Gillan, J. W., 38, 49, 53 GL Mark I, 37, 64 Initial orders, 143-4, 147, 162 GL Mark II, 64-5, 70 Institute for Advanced Study, 122, 133, GL Mark III, 62, 66 139, 148, 163, 185 Glennie, A. E., 209-10, 211 International Congress of Mathematicians, 174 G n e is n a u , 74-5, 76 International Federation for Gold, T., 127-8, 129 Goldstein, S., 13 Information Processing, see IFIP Goldstine, H. H„ 119, 122, 133, 163, 165 International Union of Geodesy and Geophysics, 112-3, 115, 203 Goodwin, E. T., 135 Ionospheric research in Germany, Gort, Field Marshall Lord, 58 99-101 Gotlieb, Kelly, 161, 162 Goto, E., 223 Jackson, Willis, 140 Gould, Lt-Cmdr, 197 Jamming of radar stations, 71-2, 74-5, Grandparents, 3, 4 83 Green Howards, 42 Jefferson, Sir Geoffrey, 195 Griffiths, J. H. E., 35 Johnson, Major P., 69 Grosch, H„ 210-11 Johnson, N. K., 74 Johnson-Ferguson, Major, 92, 93, 94, Hall, Peter, 216 97 Halsbury, Earl of, 226 Joint Computer Conference, 179, 182, Hartley, D. H., 218, 225 202, 218 Hartree, D. R., 25, 29-30, 106-8, 117, Jones, F. E., 82 122, 132, 137, 138, 140, 146, 147, Joubert, Sir Phillippe, 44, 73 150, 151, 152, 184, 195, 197, 198 Harvard Mark I, see Automatic Kelvin, Lord, 111 Sequence Controlled Calculator Kempton, A. E., 43, 45, 73, 75 Harvard Mark II, 124, 170 Kendrew, John, 191-2 Harvard Mark III, 170, 175 Kilbum, T., 134, 138, 145, 215 Harvard Mark IV, 174, 175, 190 Kinsey, B. B., 40, 43 Hasler Company, 229 Kirke, H. L., 67 Hearn, A., 222 Kjellberg, G., 144 Heaton-Armstrong, Mr, 83 Kopal, Z„ 149 Herdman, T. L., 15, 32 Korean War, 177-8 Hess, Rudolph, 66 Hey, J. B., 71-2 Lack, David, 72, 76 High level languages, 209, 224-6 Landmarks, 142 Hinde, G. H„ 144 Lang, Charles, 219-20, 221 HM Prisons, 113 LARC, 183 Hoare, C. A. R., 225 Larmor, Sir Joseph, 13 Hodge, W. V. D., 103-4 Lamder, H., 38 Hodgkin, Sir Alan, 68 Latham, R., 43, 45, 47, 49 Holland-Martin, C. G., 140-1 Lawlor, Lieutenant, 155, 156, 157, 159 Hooper, Dudley, 202 Leigh light, 85 Hopper, Grace, 167, 210 Lennaerts, E. G., 134 Howe, G. W. O., 6 Lennard-Jones, J. E., 25-30, 104, 127, Hurd, C., 183 152

Index

LEO Computers, 134 Lewis, W. B., 20, 35 Licklider, J. C., 214 Lilley, Sam, 22 Lincoln Laboratory, 214, 218 Lincoln, Mr, 22 Llandudno move of CAEE to, 60 ADRDE trials station at, 79-80 Logic, families of, 161 Logical design, 161 London Computer Group, 202 Lorenz, H. A., 13 Lovelace, Countess of, 197 Lovell, A. C. B., 35 Lyons and Company, J., 132-4 McCarthy, John, 214, 218 Machin, Pat, 170 Magnetic cores for logic, 224 Magnetic drum, 139, 145 Magnetic mines, 50, 51 Magnetic tape, 166, 169, 190-1 Magnetron, 56, 62 Mallock Machine, 27, 29, 33 Mallock, R. R. M„ 27, 29 Malvern, move of ADEE and TRE to, 78 Manchester, machines at, 145 Marconi Company, 32-3 Marconi, G., 162 Marshall, J. Stewart, 22 Massachusetts Institute of Technology visits to, 124-5, 176-7, 180-2, 214-5 Whirlwind computer at, 176, 182 core memory development at, 181-2 early time-sharing at, 214-5 Mathematical Laboratory origins of, 27-30 wartime occupation of, 30, 104-6 post war reconstruction of, 103-10 appointed Director of, 127 change of name of, 217-8 Mathematical Tripos, 10-14, 16-18, 21, 133, 135 Mauchly, John, 108-9, 119-21, 123, 160, 165-6, 168 Mauchly, Kay, 166 Mauchly, Mary, 124 May Island, 47-8, 50 Meagher, R. D., 171, 172 Medical Research Council, 215 Meinesz, Professor, 114 Memory protection, 227, 228

237

Memory Test Computer, 181-2 Menebrea, L. F., 197 Mercury memory, 121, 127-9, 131, 142, 167-8, 175, 185, 209 Microprogramming, 178, 187-8, 198 Miller, J. C. P., 179-80 Millington, D. W., 40 MIT, see Massachusetts Institute of Technology Monroe, Elizabeth, 26 Moon, P. B., 35, 36 Moore School, 14, 116, 119, 123, 132, 139, 168 Mordell, L. J., 151 Morley, E. G. T., 43 Morse, Philip, 214 Morton, P. L., 173 MOSAIC, 135 Moses, Joel, 222 Mother, 1-2, 4, 11-12 Mott, N. F„ 60, 62 Moulin, E. B., 14 Mountbatten, Lord Louis, 195 Mullard Ltd, 186 Multi-processor computers, 227-8 Multiplexer, 217 Mumford, C. M., 109-10 Munich crisis, 33-4 Mutch, E. N, 139, 149, 151, 152-3, 179, 180, 185 Nash, J. P., 171-2 National Bureau of Standards, 138-9, 165, 168-9, 173, 177 National Physical Laboratory, 109, 146, 150, 156 Mathematics Division, 109, 135, 137, 138 Naur, Peter, 151 Needham, R. M., 227-8 NELLIAC, 189 Neumann, J. von, 108-9, 116, 120, 122, 136, 147-8, 160, 163, 165, 174, 183 Newman, M. H. A., 13-4, 137, 145, 218 Newman, W., 218-9 Newton, Pat, 170 Nobel lecture, 192, 193 Noble, Ben, 140 Norman, Arthur, 221-2 Nuffield Foundation, 184, 186, 224 Nuttall, J. M., 35

238

Index

Oatley, C. W., 43, 44-5, 48, 54, 55 Oboe, 81-3 Office of Naval Research, 134, 163 Oliphant, M. L. E., 56 Operational research group, formation of, 66 ORDVAC, 171 Oxford, D. R., 70 Paper tape reader, 191 Papian, Bill, 181 Pars, L. A., 16 Paterson, Col. H. M. 79, 144 Pawsey, J. A., 20 PDS, see Post Design Services Peake, Mr, 2-3 Pearson, Karl, 204 Pekeris, C. L., I l l , 112 Pender, Harold, 116 Perlis, Alan, 177 Perutz, M. F., 191-2 Petain, Marshal, 57 Pevsner, N., 171 Phillips, Flight Sergeant, 38, 40, 41 Piggott, W. R., 158 Pike, D. F., 68 Pile, General Sir Frederick, 64-6, 68 Pinkerton, J. M. M., 134 Plant breeding, 206 Plessey System 250, 228 Porter, Arthur, 25, 30 Post Design Services, 83-5, 88 Powell, F. C., 17 Priorities Committee, 151-2 Project MAC, 214 Pye Radio, 45, 51-2 Pye, D. R., 34 Queen Mary, RMS, 125-6, 170, 178 Radar on transatlantic liner, 118 Radar, introduction to, 34-38 Radiation Laboratory, 125 Radio astronomy, 72 Radio engineering, 14-15 Radio Officers, 65 Rajchman, J. A., 121, 164, 182-3 Ramsay, J. A., 59, 77 Randall, J. T., 36, 56 Randell, Brian, 199 Ratcliffe, J. A., 18, 20-1, 24-5, 34, 41, 47, 48, 57, 65-6, 68, 70, 83, 99, 134, 140, 192 RCA, 182-3

RDF Applications Committee, 56 Rees, D., 206 Rees, Mina, 163 Reeves, A. H., 82 Reinike, Captain H. J., 75 Remington-Rand, 166 Renwick, W., 129, 132, 142 Research projects, choice of, 222-9 Reynaud, Paul, 57, 58 Richards, J. H., 40, 186 Ridenour, L. N., 172 Roberts, L. G., 213 Rochester, N., 210 Rockefeller Foundation, 148 Roof climbing, 204-5 Ross, D. T., 219 Rothamsted Experimental Station, 204, 206-7 Rowe, A. P., 36, 43, 52, 78 Rubinoff, Morris, 168 Rutherford, Lord, 24-5, 28 Ryle, Martin, 192, 193 Sadler, D. H., 109 St John’s College joining, 9-10 Adams Memorial prize, 17 life at BA Table, 22 graduate croquet club, 23-4 fellowship, 171 Samuel, Arthur, 167, 197, 21 1 Saunders, J. T., 104-5, 116 Sayer, Brigadier A. P., 75 S c h a r n h o r s t, 74-5, 76 Schnorkel, 88 Schonland, B.J. F., 69-70, 71, 74, 76, 77 Science Museum, 189, 197, 198, 199 Scorer, R. S., 148 Scott, Dana, 226 SEAC, 168, 177 Searchlight radar, 70-1 Selective Sequence Electronic Calculator, 168 Selectron, 121-2, 164 Seminars, see Colloquia Shackleton, Sir Ernest, 10 Shearer, Dr, 104, 106 Shelley, Elsa, 126 Shire, E. S., 43, 45, 46, 55, 62, 65 Sideband controversy, 6, 138 SILLIAC, 171 Sketchpad, 218, 221 Skiatron, 69

Index

Skinner, H. W. B., 35, 36 SLC, 70-1 Smith, A. E„ 122 Smith, C. L., 38, 40 Smith, C. V. L., 163, 164 Smith, Sir Frank, 65 Solid modelling, 220 Somerville, Admiral Sir James, 44, 47, 48, 49 Space cadets, 210 Space War, 218 Spitzer, Lyman, 22-3 Standard Telephones and Cables Ltd, 82, 83 Stanesby, Harold, 81 Stanley, J. P., 147 Statistical calculations, 206-7 Stenode Radiostat, 6, 138 Stevens, G. J., 129, 142 Stoneley, R. S., 103-4 Strachey, Christopher, 189, 226-7 Stratford, F. J., 17, 24 Studdert, Commander, 154-5, 158 Submarine campaign, 85-9 Subroutines, 143, 144, 146-7, 150, 169, 180 Summer School, 149-50 Sumner, Frank, 214 Sunday Soviets, 89 Sutherland, Ivan, 218, 219 SWAC, 139, 168, 170, 173 Swann, Michael, 77 Swann, Mr, 141 Swedish Board for Computing Machinery, 144, 190 Swinney, Warrant Officer, 51 System Development Corporation, 214 Tausky, Olga, 169 Taylor, G. I., I l l , 112 Taylor, Norman, 181-2 Taylor, W. H., 142 Thinking machines, 195-7 Thomas, Captain, 94 Thomas, H. A., 138 Thompson, Andrew, 162 Thompson, T. R., 132-3 Timbrell, J., 7-8 Timesharing, 214-7 Titan computer, 216-218, 224 Tizard, Sir Henry, 34, 62 Todd, J. A., 109, 169 Toulmin, Steven, 101-2 Transistors, introduction of, 213

239

TRE move to Dundee, 43 CHL responsibility, 53 move to Worth Matravers, 78 service at TRE, 80, 81-9 Trethowan, Don Illtyd, 196 Trials group (ADEE), 57-62 Tropp, H. S., 200 Tunnel diodes, 223-4 Turing, Alan, 135-7, 145-6, 196-7 Turner, L. B., 14-15 Turski, W. L., 204 Twyman, F., 103 Twyman, Nina, see Wilkes, Nina U-boats, 85-9 UNESCO, 203, 204 United Kingdom Automation Council, 202

UNIVAC, 166-8, 183 US Army Proving Ground, 165, 169 Van Horn, E. C., 227 Varley, G. C., 68, 72-3, 74, 76, 79 Varley, Philip, 72, 79 Vint, Jimmy, 59, 79 Vollum, Lieutenant, 75 von Neumann, J., 108-9, 116, 120, 122, 136, 147-8, 160, 163, 165, 174, 183 Walther, A., 144, 156-7 Walther, Frau, 157 Watson-Watt, R., 34, 35, 36, 44, 52, 94 Webber, Flight-Lieutenant N. V., 53 Weekes, Kenneth, 36, 111-2, 141, 156 Weygand, Marshall, 58 Wheeler, D. J., 142, 143-4, 146, 147, 148, 149, 162, 163, 165, 171-2, 173, 180, 187-8, 189, 193, 210, 217, 228 Wheeler, Joyce, 188 Whirlwind, 176, 178, 181-2, 185, 214 White, E. L. C., 20 White, F. P„ 13-14 White, F. W. G., 20 Wijngaarden, A. van, 144 Wilkes, Nina, nee Twyman, 125, 130, 147, 170-1, 229 Wilkes, Wheeler, and Gill, 149, 180, 209 Wilkins, A. F., 36 Wilkinson, J. H., 138 Williams tube memory, 164, 169, 171, 172, 185, 209

240

Index

Williams, F. C., 134-5, 138, 145 Willis, D. W., 190 Wilson, C. T. R., 24 W ir e le ss W o r ld , 5-6 Wirth, Nildaus, 225 Wiseman, N. E., 218, 219, 221, 223 WISP, 189-90 Womersley, J. R., 135, 137 Woodward, F. H., 17 Wordie, J. M., 9-10, 22, 114 World War I, 1, 31 Worth Matravers, move of TRE to, 56 Wynn-Williams, C. E., 35 X-ray crystallography, 141-2, 191-2 Yates, Frank, 204-5 Yngve, Victor, 227 Young, H. S., 57, 64 Zennech, Professor, 101 Zugspitze, 100-1 Zuse, K., 157

The MIT P«

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