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Railways authority.^19 Turing and Twinn took this on. Colonel John Tiltman had broken into
Railway Enigma, helped by what he called the ‘very stereotyped pro-forma nature’ of the
German messages.^20 We knew that messages of a stereotyped nature were easy prey to crib-
based attacks. Turing came over to look at Dilly’s crib charts. Italy had just come into the war,
and we had found an Italian crib chart from the Spanish Civil War—the railway machine and
the machine used by the Italians were closely related.
Soon after this, Turing decided to compile his newcomers’ manual, ‘Prof ’s Book’. Chapter 1
set out the workings of the Enigma machine, while Chapters 2 and 3 described Dilly’s rodding
methods and his ‘saga’ system for finding wheel wirings. Turing recalled the pre-war work on
the monster crib supplied by the German cipher office, observing that at least a ninety-letter
crib was necessary for success with the saga method.^21 Chapter 4 covered the ‘Unsteckered
Enigma’, including Railway Enigma and Italian military Enigma, and Turing mentioned the
Italian crib chart that we had found—although he copied it out wrongly! It is because Turing
gave examples from Railway Enigma that the Knoxian methods he was using have sometimes
been said to be his own—but he himself never made such claims. His own work, on Naval
Enigma and the bombe, appeared in the final chapters.
Parts of ‘Prof ’s Book’ were released in 1996 by the US National Security Agency, as was Patrick
Mahon’s ‘The history of Hut Eight, 1939–1945’, early chapters of which described Turing’s his-
toric attack on Naval Enigma. As a result, Turing’s monumental cryptographic achievements
are now understood and appreciated. Dilly, on the other hand, left few records, and for security
reasons his section’s history remained classified until 2011.
Conclusion
At the end of 1941, when terminally ill, Dilly broke the most difficult multi-turnover Enigma
machine, used by the Abwehr, the equivalent of Britain’s MI5 and MI6.^22 We liaised with him
at his home for the remaining months of his life. At this time a new section called Intelligence
Services Knox (ISK) was set up, headed by Twinn, and Keith Batey also joined us. At GCHQ
(Government Communications Headquarters, the modern equivalent of Bletchley Park) the
official report describing the work of ISK is known simply as ‘BBR&T’, after its authors, Keith
Batey, myself, Margaret Rock, and Peter Twinn, and it describes how ten differently wired
Enigma machines were broken using Dilly’s methods.^23
In summary, the young Turing’s early association with veteran codebreaker Dilly Knox was
a key factor in Bletchley Park’s great successes against Enigma.