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your son’s work in the 1930s laid the theoretical foundations for the modern computer and
that the Foreign Office’s special purpose computer was, to their belief, the first such electronic
computer to be constructed anywhere. Moreover, they credited your son’s work with having
had a considerable influence on the design of this machine.
Further, a book has recently been published in the United States entitled Bodyguard of Lies
which describes the work of the Allies during the war to deceive the Germans and to prevent
them from anticipating the D-day invasion. This book credits your son as being the main person
involved in the breaking of one of the most important German codes, the Enigma Code, and
thus implies that his work was of vital importance to the outcome of World War II. This latter
information in the book Bodyguard of Lies is not, of course, official information but nevertheless
it will, I believe, enable many people to obtain a yet fuller understanding of your son’s genius. I am
very pleased that this is now happening.
I was delighted to receive a very nice reply from Mrs Turing, dated 2 December 1975, saying
that she was ‘very much gratified’ by my letter, and that she regarded it of such importance that
she would like to have a few photostat copies so that she could distribute them.
During the period October–December 1975 I interviewed the leading Colossus design-
ers: Tommy Flowers, Bill Chandler, Sidney Broadhurst, and Allen ‘Doc’ Coombs. I found
all four of them to be delightful individuals, immensely impressive and amazingly modest
about their achievements. All were unfailingly pleasant and helpful as they tried to recollect
happenings at Dollis Hill and Bletchley Park. I had the further pleasure of interviewing Max
Newman and Donald Michie, and David Kahn kindly interviewed Jack Good for me at his
home in Roanoke, Virginia. I also corresponded, in some cases quite intensively, with all
these interviewees and with a considerable number of other people, including several of
the Americans who had been stationed at Bletchley Park. Indeed, it was one of these who
alerted me to what had been said in the Washington Post in 1967 in a review of Kahn’s book
The Codebreakers:^4
Magnificent as the book is, it is like a history of English drama that takes no account of Shakespeare.
Kahn notes, correctly, that 30,000 people were involved in cryptanalysis in Britain during World
War II . . . In importance, not to mention drama and sheer intellectual brilliance, the British effort
pales every other account in Kahn’s huge book, or perhaps all of them combined.
Each interview was tape-recorded, and I had the tapes transcribed in full. The people I inter-
viewed and corresponded with were being asked to recall happenings of thirty or so years ear-
lier, and to do so without any opportunity of inspecting original files and documents. Secrecy
considerations had been paramount, and had given rise to a rigid compartmentalization of
activities. Few had any detailed knowledge of the work of people outside their own small group.
Many of them had made conscious efforts to try and forget about their wartime work.
Piecing together all the information I thus obtained, and even establishing a reasonably
accurate chronology, was therefore very difficult. I was greatly aided in this task by the advice
I had read in Kenneth May’s magnificent Bibliography and Research Manual on the History of
Mathematics;^5 for example, the techniques that he described for creating and using a set of cor-
related card indexes greatly helped me in sorting out a major chronological confusion amongst
my interviewees concerning the development of the Robinson machines. The indexes that I
constructed employed unpunched IBM cards, rather than conventional index cards. They filled
a standard box, so I knew that there were approximately 2000 of them.