The Bletchley Park Codebreakers Read online

  In September 1920, the Daily Mail and the Morning Post published details from the decrypts of secret Soviet subsidies to the socialist Daily Herald. In May 1923, the Cabinet authorized the Foreign Secretary, Lord Curzon, to quote Soviet diplomatic decrypts in a protest note to Moscow, chiefly concerned with Soviet subversion in India and India’s neighbours. The protest note, swiftly christened the ‘Curzon ultimatum’, was unprecedented in the history of British diplomacy. Not content with quoting from Soviet decrypts, Curzon repeatedly taunted Moscow with the fact that its secret telegrams had been successfully intercepted and decrypted by the British:

  The Russian Commissariat for Foreign Affairs will no doubt recognize the following communication dated 21st February 1923, which they received from M. Raskolnikov … The Commissariat for Foreign Affairs will also doubtless recognize a communication received by them from Kabul, dated the 8th November, 1922 … Nor will they have forgotten a communication, dated the 16th March 1923, from M. Karakhan, the Assistant Commissary for Foreign Affairs, to M. Raskolnikov …

  The new ciphers, introduced by Moscow in an attempt to make its diplomatic traffic more secure after the Curzon ultimatum and other British breaches of Sigint security in the early 1920s, were successfully broken by British cryptanalysts after varying intervals. In 1927, however, Britain’s ability to decrypt Soviet diplomatic traffic was fatally undermined by another extraordinary governmental indiscretion. The Baldwin Cabinet, of which Churchill was a member, decided to publish a selection of Soviet intercepts in order to justify its decision to break off diplomatic relations with Moscow. Austen Chamberlain, the Foreign Secretary, gave his message to the Soviet chargé d’affaires breaking off relations a remarkably personal point by quoting a decrypted telegram from the chargé to Moscow ‘in which you request material to enable you to support a political campaign against His Majesty’s Government’. A. G. Denniston, the operational head of GC&CS, wrote bitterly that Baldwin’s government had deemed it ‘necessary to compromise our work beyond question’. Henceforth Moscow adopted the theoretically unbreakable ‘one-time pad’ for its diplomatic traffic. For the next twenty years British cryptanalysts were able to decrypt almost no high-grade Soviet diplomatic traffic (though they continued to have some success with communications of the Communist International).

  The lessons learned from the Sigint catastrophe of 1927, as a result of which Britain lost its most valuable interwar intelligence source, were crucial to the later protection of the Ultra secret. 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 soap and steam. Frank Birch wrote affectionately of Knox in his classified satirical history of Room 40, Alice in ID25:

  The sailor in Room 53

  has never, it’s true, been to sea

  but though not in a boat

  he has served afloat –

  in a bath in the Admiralty.

  Knox’s bathtime cryptanalysis continued during his time at Bletchley Park, once causing fellow lodgers at his billet, when he failed to respond to shouted appeals through the bathroom door, to break down the door for fear that he might have passed out and drowned in the bath.

  Turing’s eccentricities make such engaging anecdotes that they are sometimes exaggerated, but there can be no doubt about their reality. His ability from a very early age to disappear into a world of his own is wonderfully captured by a drawing of him at prep school by Turing’s mother, which she presented to the school matron. The drawing, entitled ‘Hockey or Watching the Daisies Grow’, shows the ten-year-old Turing, oblivious of the vigorous game of hockey taking place around him, bending over in the middle of the pitch to inspect a clump of daisies. At Bletchley Park he chained his coffee mug to a radiator to prevent theft, sometimes cycled to work wearing a gas mask to guard against pollen, and converted his life savings into silver ingots which he buried in two locations in nearby woods. Sadly, he failed to find the ingots when the war was over. The informality and absence of rigid hierarchy at Bletchley Park enabled it to exploit the talents of unconventional and eccentric personalities who would have found it difficult to conform to military discipline or civil service routine.

  Most of the dons and other professionals recruited by Room 40 had been young. The ‘professor types’ selected by Bletchley Park were, on average, younger still. In the summer of 1939, Alastair Denniston wrote to the heads of about ten Cambridge and Oxford colleges, asking for the names of able undergraduates who could be inter
viewed for unspecified secret war work. Among the twenty or so recruited during the first round of interviews (repeated on a number of later occasions during the war) was the twenty-year-old Harry Hinsley, who was about to begin his third year as an undergraduate historian at St John’s College, Cambridge. After Pearl Harbor, when Bletchley Park needed more cryptanalysts and linguists to take newly devised crash courses in the Japanese language, the recruitment included sixth-formers as well as undergraduates – among them Alan Stripp, recruited after winning a classics scholarship to Trinity College, Cambridge, who later co-edited with Hinsley a volume of memoirs on Bletchley Park. During a visit to Bletchley, Churchill is said to have remarked ironically to Denniston, as he surveyed the unusually youthful staff, ‘I told you to leave no stone unturned to get staff, but I had no idea you had taken me literally.’

  Recruitment to Bletchley Park broke with one important but misguided precedent established during the First World War. Room 40 had made no attempt to recruit professional mathematicians, whose supposedly introverted personalities were thought to be too far removed even from the realities of daily life for them to engage with the horrendous problems posed by the First World War. Though a prejudice normally associated with arts graduates, this jaundiced view of mathematicians appears to have been shared by the Director of Naval Education, Sir Alfred Ewing, a former Fellow of King’s and Professor of Engineering at Cambridge, who seems to have been chiefly responsible for the recruitment from King’s (where his son-in-law remained a Fellow) of Adcock, Birch and Knox. Despite his own mathematical training, Ewing evidently considered the experience of classicists, historians and linguists in making sense of difficult and complex texts a more relevant skill for cryptanalysis than mathematical expertise. Similar prejudices continued to influence the recruitment of British cryptanalysts between the wars.

  Polish military intelligence realized at the end of the 1920s that the attempt to break Enigma would require the recruitment of professional mathematicians (one of whom, Marian Rejewski, was to make the first major breakthrough in the attack on it). In the summer of 1938, Denniston finally reached a similar conclusion and began including a limited number of mathematicians among the ‘professor types’ who were being earmarked for Bletchley Park. Initially, however, the mathematicians were treated with considerable caution and some suspicion. The first mathematics graduate recruited by GC&CS, Peter Twinn of Brasenose College, Oxford, was told after he began work early in 1939, that ‘there had been some doubts about the wisdom of recruiting a mathematician as they were regarded as strange fellows, notoriously unpractical’. Twinn owed his recruitment, at least in part, to his postgraduate work in physics. Physicists, he was told, ‘might be expected to have at least some appreciation of the real world’ – unlike, it was believed, most mathematicians.

  Though the first wave of ‘professor types’ to arrive at Bletchley Park at the outbreak of war consisted chiefly of linguists, classicists and historians, it also included two brilliant Cambridge mathematicians: Turing from King’s and Gordon Welchman from Sidney Sussex College, who may originally have been earmarked because his mathematical brilliance was combined with skill at chess. According to the Cambridge Professor of Italian, E. R. ‘Vinca’ Vincent – probably the first ‘professor type’ to be selected – ‘Someone had had the excellent idea that of all people who might be good at an art that needs the patient consideration of endless permutations, chess players fitted the bill.’ Among other chess experts to arrive at Bletchley Park in the early months of the war were Hugh Alexander and Stuart Milner-Barry. Turing, Welchman, Alexander and Milner-Barry were jointly to sign the celebrated Trafalgar Day memorandum in 1941, which Churchill minuted, ‘Action This Day’. Whatever the original reasons for their recruitment, the first professional mathematicians at Bletchley Park made themselves indispensable so quickly that the recruiting drive was rapidly extended to mathematicians without a reputation as chess players.

  Though GC&CS operated on a very much larger scale after its wartime move to Bletchley Park than it had done between the wars, at least one aspect of its original organization remained both of crucial importance and considerably ahead of its time. Denniston considered the ‘official jealousy’ which had prevented any collaboration between naval and military cryptanalysts from October 1914 to the spring of 1917 ‘the most regrettable fact’ in the history of British wartime Sigint. The establishment of GC&CS in 1919 was intended to avoid any repetition of such interdepartmental feuding. Within a few years of its foundation the new agency achieved the successful co-ordination of diplomatic and service cryptanalysis under overall Foreign Office control, though for most of the interwar years diplomatic decrypts yielded much more valuable intelligence than service traffic. That co-ordination, equalled by no other major Sigint agency abroad, was one of the secrets of Bletchley Park’s success.

  For much of the 1930s the bitter rivalry between US naval and military Sigint agencies closely resembled that between their British counterparts during the First World War. Each sought to crack independently the same diplomatic codes and ciphers in order, according to a declassified official history, to ‘gain credit for itself as the agency by which the information obtained was made available to the Government’. Though there was limited interservice collaboration at the end of the decade, the rivalry resumed after the breaking of the Japanese Purple diplomatic cipher by military cryptanalysts in September 1940, as naval codebreakers sought to prevent the Army from monopolizing Magic (Japanese diplomatic decrypts). After lengthy negotiations, an absurd bureaucratic compromise was agreed, allowing the military Signal Intelligence Service (SIS) to produce Magic on even dates, and its naval counterpart, OP-20-G, to do so on odd dates. This bizarre arrangement continued to cause confusion until the very eve of Pearl Harbor. On the morning of Saturday 6 December, a naval listening post near Seattle successfully intercepted thirteen parts of a fourteen-part message from Tokyo to the Japanese embassy in Washington, rejecting US terms for a resolution of the crisis and making clear that there was no longer any prospect of a peaceful settlement. (The fourteenth part was intercepted on the following day.) This critically important intercept was forwarded by teleprinter to the Navy Department in Washington. But since 6 December was an even date, the Navy Department was obliged to forward the message to the military SIS for decryption shortly after midday. SIS, however, found itself in a deeply embarrassing position since its civilian translators and other staff, as usual on a Saturday, had left at midday and there was no provision for overtime. Doubtless to its immense chagrin, SIS was thus forced to return the intercept to the Navy. While OP-20-G began the decryption, SIS spent the afternoon gaining permission for its first Saturday evening civilian shift. By the time the shift started, however, it was too late for SIS to reclaim the partly decrypted intercept from OP-20-G. And so, for the first time, on the eve of Pearl Harbor, the rival agencies produced Magic together. SIS was able to decrypt two of the thirteen parts of the intercepted Japanese message, though the typing was done by the Navy. The Sigint confusion in Washington, at one of the most critical moments in American history, highlights the immense importance of the successful resolution of interservice rivalry by GC&CS two decades earlier.

  Equally essential to Bletchley Park’s success was Churchill’s passion for Sigint. By a remarkable – and fortunate – coincidence, Churchill became war leader shortly after the first Enigma decrypts, one of the most valuable intelligence sources in British history, began to come onstream. Churchill’s passion for Ultra was equalled only by his determination to put it to good use. On the tenth anniversary in 1924 of the founding of Room 40, he had described Sigint as more important to the making of foreign and defence policy than ‘any other source of knowledge at the disposal of the state’. He was also well aware that, despite some successes during the First World War, the advantage gained by breaking German codes had sometimes been wasted. The indecisive battle of Jutland in 1916, the greatest naval battle of the war, might well hav
e ended in a decisive British victory if the Sigint provided by Room 40 had been properly used by the Admiralty. Churchill’s own use of Ultra during the Second World War was, of course, far from infallible. The exaggerated sense of Rommel’s weakness in North Africa which he derived from his over-optimistic interpretation of Enigma decrypts, for example, made him too quick to urge both Wavell and Auchinleck to go on the offensive.

  Even when due account is taken of Churchill’s limitations, however, he still remains head and shoulders above any other contemporary war leader or any previous British statesman in his grasp of Sigint’s value. That grasp depended on an experience of Sigint which went back to the founding of Room 40 early in the First World War and on his ability to learn from his mistakes in the handling of it. Had Churchill come to power in May 1940 without previous experience of Sigint, Bletchley Park might well have found his untutored enthusiasm for Ultra a dubious asset.

  Great war leader though he was in most other respects, President Franklin D. Roosevelt was simply not in Churchill’s class when it came to Sigint. Despite a general awareness of the importance of wartime intelligence and a particular fascination with espionage, dating back to his experience of naval intelligence in the First World War, Roosevelt failed to grasp the importance of Sigint. Though Magic provided by far the best guide to Japanese policy during the year before Pearl Harbor, he showed only a limited interest in it. As well as sanctioning the absurd odd-even date division of labour between naval and military cryptanalysts, he also agreed to a further bizarre arrangement by which his naval and military aides took turns in supplying him with Magic in alternate months. This arrangement led to predictable confusion, including the suspension of the Magic supply in July 1941, after FDR’s military aide breached Sigint security by absentmindedly leaving Japanese decrypts in his wastepaper basket. Not until November did the President finally lose patience and insist that Magic henceforth be communicated to him exclusively through his naval aide, Captain John R. Beardall. When shown Japanese decrypts, Roosevelt very rarely commented on them. Not until three days before Pearl Harbor did he discuss with Beardall the significance of any of the Magic revelations.