The Bletchley Park Codebreakers Read Free

No politician took those lessons more to heart than Winston Churchill. After he became prime minister, at his personal insistence the circle of those who shared the secret of the cryptanalysts’ ‘golden eggs’ was limited to only half a dozen of his thirty-six ministers. The Special Liaison Units set up to pass Ultra to commanders in the field were the most sophisticated system yet devised to protect the wartime secrecy of military intelligence. The profound change in Churchill’s attitude to Sigint security is epitomized by the contrast between his published accounts of the two world wars. In his memoirs of the First World War, Churchill had written lyrically of the importance of Sigint; in his memoirs of the Second World War there is no mention of Ultra.
    As well as being crucially dependent on the lessons learned in 1927, Ultra also owed much to precedents set in the First World War. The creation of GC&CS in 1919 was itself a consequence of the fact that Sigint had proved its value during the war. Without the expertise painstakingly built up by Denniston on minimal resources between the wars, Bletchley Park’s wartime triumphs would have been impossible – despite the invaluable assistance provided by the Poles and French on the eve of war. The breaking of Enigma in its wartime variations required a major new intelligence recruitment. In 1937, the Chief of the Secret Service, Admiral Sir Hugh ‘Quex’ Sinclair, told Denniston that he was now ‘convinced of the inevitability of war’ and gave‘instructions for the earmarking of the right type of recruit immediately on the outbreak of war’ – chief among them what were quaintly called ‘men of the professor type’. The most active recruiters of ‘professor types’ were two Fellows of King’s College, Cambridge, who had served in Room 40, the main First World War Sigint agency: Frank Adcock (later knighted), Professor of Ancient History, and the historian Frank Birch, who left Cambridge for the stage in the 1930s. Both inevitably looked for recruits in the places they knew best: Cambridge colleges in general and King’s in particular. A total of twelve King’s dons served at Bletchley during the Second World War. By great good fortune the King’s Fellowship included Alan Turing, still only twenty-seven at the outbreak of war, one of the very few academics anywhere in the world to have carried out research into both computing and cryptography. Turing’s pioneering paper, ‘Computable Numbers’, now recognized as one of the key texts in the early history of modern computer science, was published early in 1937, though it attracted little interest at the time. Three months before its publication Turing, then at Princeton, wrote to tell his mother that he had also made a major breakthrough in the construction of codes. In view of his later exploits at Bletchley Park, Turing’s letter now seems wonderfully ironic:
    I expect I could sell [the codes] to HM Government for quite a substantial sum, but am rather doubtful about the morality of such things. What do you think?
    Turing went on to become the chief inventor of the ‘bombes’ used to break Enigma.
    The search for ‘professor types’, of whom Turing was probably the most remarkable, even in a highly distinguished field, followed two important precedents established during the selection of British codebreakers in the First World War: the recruitment of unusually youthful talent and of original minds who would have been regarded as too eccentric for employment by most official bureaucracies. (The two categories, of course, overlapped.) Two of Britain’s leading codebreakers in the two world wars, Dillwyn ‘Dilly’ Knox and Alan Turing, both Fellows of King’s, were also among the most eccentric. Knox, a classicist, did some of his best work for Room 40 lying in a bath in Room 53 at the Admiralty Old Building on Whitehall, claiming that codes were most easily cracked in an atmosphere of soapand