The Bletchley Park Codebreakers

by Michael Smith

  Chapter 13 tells a truly remarkable story, which reflects greatly to the credit of three men in particular, William Friedman, Telford Taylor and John Tiltman: they are shown to have been men of real vision, blessed with good judgement - and to have been much needed at the time.

  RE

  In July 1942, a Bletchley Park liaison officer arrived in Washington and immediately began venting his considerable annoyance with Britain’s ally in a series of increasingly exasperated despatches. There was the unbearable ‘regimental gossip’ of American wives at dinner parties. There was an absurd and tedious picnic he was dragged to in Washington’s Rock Creek Park. There was ‘our fat friend Kully’ – Solomon Kullback, one of the US Army’s leading cryptanalysts – who over-organized his section, placed obstacles in the way of British requests for information, and had the habit, ‘which I am sure you must have observed in some degree, of shouting people down to contradict something they have no intention of saying’. By September the British official was writing home:

  Sometimes I think they are just a lot of kids playing at ‘Office’. You must have noticed yourself how very many childish qualities the American male has: his taste in women, motor-cars, and drink, his demonstrative patriotism, his bullying assertion of his Rights, his complete pig-selfishness in public manners and his incredible friendliness and generosity when he likes you – Hell! anyone would think I didn’t like them. But perhaps it is as well I’m fond of children.

  Even with America’s entry into the war in December 1941, it was far from inevitable that the two allies would forge any real or meaningful co-operation in cryptanalysis and signals intelligence. There was certainly a lot working against it. For a start, the British were convinced that the Americans were simply incapable of safeguarding important secrets. Many Bletchley Park officials were loath to share their monopoly over the control and distribution of intelligence derived from the breaking of the German Enigma ciphers. On the American side, the US Navy might have finally forgotten the war of 1812 and the press-ganging of American sailors, but nonetheless harboured a widespread distrust and resentment of the British, and was particularly touchy about anything that might imply that America was a junior partner taking orders from the British. Moreover, many American officials (with good reason, given past practice of GC&CS) were suspicious that the British would exploit cryptologic co-operation to gain access to American codes in order to read confidential US diplomatic communications.

  Finally, there was the simple transatlantic culture gap – far greater then than now – that led to repeated misunderstandings, friction and enmity on a personal level, of the sort so richly exemplified by Bletchley Park’s liaison officer, who, when he was not penning poisonous despatches, was irking the US Army code-breakers at Arlington Hall with what many took to be his pompous and overbearing manner. (One Arlington Hall veteran recalled that this officer always appeared with Sam Browne belt, polished riding boots and swagger stick.)

  In the end it was a combination of practical necessity and personal diplomacy that overcame these many obstacles and helped to launch the ‘special relationship’ between the British and American intelligence agencies, which endures to this day. The pooling of talent, effort and technology by British and American cryptanalysts proved to be of the first importance in the breaking of the German U-boat ciphers and diplomatic codes and the Japanese naval and military codes in particular. But it was a long haul, and were it not for a few far-sighted and level-headed men on both sides of the Atlantic who prevailed at critical junctures, the relationship would never have progressed beyond the ‘make polite noises’ stage at which it was largely stuck for the first couple of years of the war. The real heroes of this tale are John Tiltman on the British side and William Friedman and Telford Taylor on the American side, and perhaps even more importantly, the many lower-ranking technical experts on both sides who began working with one another at a very practical level and forged personal ties that did much to overcome the mutual suspicion and incomprehension that had threatened to poison the relationship before it had even started.

  The half century that has passed since the Second World War has brought about such a thorough revolution in travel and communication that it is difficult for us today to realize just how insular Britain and America were in 1940, and the extent to which cultural differences posed a significant obstacle to establishing co-operation. The knowledge that even many well-educated Britons had of Americans was limited to the actors they had seen on movie screens. Within official circles in Britain, Americans were frequently portrayed in the broadest caricatures: naive in the ways of the world and incapable of keeping a secret.

  On 15 November 1940, in a memorandum discussing the first feelers for co-operation with the US signals intelligence agencies, Alastair Denniston – then the operational head of GC&CS – warned that ‘we are entitled to recall that the Americans sent over at the end of the last war the now notorious Colonel [Herbert O.] Yardley for purposes of co-operation. He went so far as to publish the story of his co-operation in book form.’ Even after the US Navy had begun convoying merchant ships to Iceland and had become engaged in what was for all intents and purposes an undeclared war in the Atlantic in 1941, British officialdom was set against sharing the fruits of signals intelligence with the United States. Brigadier Stewart Menzies, who as ‘C’ oversaw both GC&CS and the Secret Intelligence Service (MI6), wrote to Prime Minister Winston Churchill on 24 June 1941 that he had considered the matter ‘from all angles’; true, US Navy units were being chased by U-boats – just four days earlier U-203 had pursued the American battleship Texas for 140 miles between Greenland and Iceland and had repeatedly tried to manoeuvre into position to fire a torpedo – and, true, GC&CS was reading Enigma traffic that contained orders from the German Admiral Commanding U-boats to his captains at sea, which might give vital warning to the Americans. But, ‘C’ concluded:

  I find myself unable to devise any safe means of wrapping up the information in a manner which would not imperil this source … it [is] well nigh impossible that the information could have been secured by an agent, and however much we insist that it came from a highly placed source, I greatly doubt the enemy being for a moment deceived, should there be any indiscretion in the USA. That this might occur, cannot be ruled out, as the Americans are not in any sense as security-minded as one would wish, and I need only draw your attention to the attached cutting from to-day’s ‘Daily Express’ on a matter which, in my opinion, should not have been made public if the two Secret Services are to work together.

  The attached article that had caught ‘C”s attention reported that Colonel William ‘Wild Bill’ Donovan ‘has a new hush-hush mission – to supervise the United States Secret Service and ally it with the British Secret Service … The American “Mr. X”, as he is known privately, will report direct to the President.’ It wasn’t exactly ‘hush-hush’ by the time the story had appeared in the Daily Express, and ‘C’ had a point.

  Although the US Army’s Signal Intelligence Service, under the direction of the renowned cryptanalyst William Friedman, was eager to initiate a sharing of technical data with GC&CS in the autumn of 1940, the US Navy was almost completely opposed to all of Friedman’s recommendations. Commander Laurance Safford, Friedman’s counterpart as head of the Navy’s OP-20-G, rejected any exchange of cryptanalytic data and techniques or training materials. Neither Friedman nor Safford, however, was interested in letting the British in on American cryptographic secrets – that is, the business of codemaking as opposed to code-breaking. In particular, Friedman ruled out giving the British ‘information of any kind’ relating to America’s SIGABA cipher machine, even the very fact of its existence. There was considerable suspicion – again not unjustified, as it happened – that the British were attempting to read American codes. Even while proposing an intimate exchange of highly secret material on codebreaking Friedman was not going to give the British anything that might help them break American systems. (After America
’s entry into the war following the Pearl Harbor attack, Churchill felt he needed to warn his new ally about the insecurity of her diplomatic codes; in a letter to President Roosevelt on 25 February 1942, the Prime Minister wrote:

  Some time ago … our experts claimed to have discovered the system and constructed some tables used by your Diplomatic Corps. From the moment when we became allies, I gave instructions that this work should cease. However, danger of our enemies having achieved a measure of success cannot, I am advised, be dismissed.

  On the one hand it was a considerate gesture, but it also confirmed the US experts’ worst fears about the British. The following year, Colonel Alfred McCormack, a US military intelligence officer, visited the British radio intercept station at Beaumanor, and while the station’s commander was showing him around he casually remarked that he used to read the US State Department ciphers and that it had been ‘lots of fun’.)

  Of course, a far greater obstacle was that the British and American signals intelligence establishments had very different aims; each wanted to extract something quite different from the other, and some of those goals were mutually exclusive. When the first technical exchanges between the two sides began in February 1941 with the arrival of a combined US Army–Navy liaison mission, Britain’s chief concern was gaining assistance in dealing with Japanese codes. Though the British had begun in the 1930s to intercept Japanese naval traffic from a station in Hong Kong (the station moved to Singapore in September 1939 and Kilindini, Kenya, in 1942 as the Japanese Army advanced through South Asia) – and though they had made some progress against the main Japanese naval operations code (the system that would later be known as JN-25) – Britain had a critical shortage of Japanese linguists. The codebook change that the Japanese Navy introduced in December 1940, replacing the JN-25A code with the much more complex JN-25B code, was a considerable setback, and the British frankly conceded that they very much needed American assistance. In fact, the British offered to turn over their entire Far East codebreaking operation to the Americans if the United States would supply the needed translators.

  In its efforts against the high-level Japanese diplomatic cipher, Purple, which was generated by a machine roughly equivalent in complexity to the German Enigma, GC&CS was also stymied and very eager for US help. GC&CS had broken the relatively simple Japanese Red machine, which had been used for diplomatic traffic for much of the 1930s, but had actually given up trying to solve the more complex Purple machine, which came into use on 20 February 1938. From the start, the British consistently sought to keep Anglo-American cryptanalytical co-operation principally limited to the one area where they knew they needed help – Japan.

  At a higher level of diplomatic calculation, Britain also was seeking to budge America away from her neutrality, and Churchill in particular saw technical exchanges among military experts in many areas as one way to do so. In a frank speech to the House of Commons, Churchill said his aim was to see the United States and Britain ‘somewhat mixed up together’. In growing numbers, American military experts began arriving in Britain in the summer of 1940 to study how the British military was performing in the fight against Germany, and they were handed reams of data on the effectiveness of fighter and bomber aircraft, on radar, and other extremely secret information. Co-operation on intelligence was just one dimension of a much broader British charm offensive, and it apparently so overwhelmed American Brigadier General George V. Strong (who in August had cabled back that Britain was ‘a gold mine’ of technical information) that in September Strong, on his own initiative, asked the British if they would be interested in a full exchange of codebreaking results, including US work on Japanese diplomatic ciphers. The British staff officials were astonished, but immediately accepted.

  Strong then had to convince Washington. He cabled, asking for an urgent reply. William Friedman at the SIS immediately saw the advantages. Though he did not know of British progress against the Enigma, he was well aware how behind the United States was in dealing with German military traffic in general. German signals were impossible to pick up from the continental United States, and the Army was essentially devoid of knowledge about the German military cryptographic systems. The US Army had not even begun paying much attention to German traffic, military or diplomatic, until October 1939, concentrating instead on Japan, Russia and Mexico. The benefits of an exchange of raw traffic, at a minimum, were manifest. Friedman was more cautious about the idea of exchanging cryptanalytic research or results, but thought it might work on a strict item-by-item quid pro quo.

  The US Navy, for its part, had been able to intercept some Enigma signals from the east coast of the United States, but had made no significant progress in decrypting the material – and it had a growing need for operational intelligence about German U-boats. Yet the Navy was so suspicious of British motives that Safford would agree to nothing beyond an exchange of traffic.

  By the late autumn of 1940, the US Navy had at last agreed to go along with Friedman’s proposal to exchange technical data with GC&CS, and the British had agreed to accept a visit by American technical experts. Roosevelt gave his blessing on 24 October and the next day the US Army’s chief signal officer. General Mauborgne, forwarded to the US Army staff a list of what the SIS proposed giving to the British – including its solution of the Purple machine. But this was far from constituting a formal agreement. The planned visit by the American technical experts was viewed by both sides as really just an initial exploratory conversation. And internal British memoranda make abundantly clear that the British plan was to stonewall if questions about the Enigma came up: the British directors of military, air and naval intelligence conferred and concluded that ‘a full interchange on Germany and Italy cannot be entertained at this stage’. Instead, when the American ‘expert’ arrived, ‘steps will be taken to steer him away from our most secret subjects’:

  Should this expert make a favourable impression, we could consider opening out on the Italian material, and possibly discuss generally ‘Y’ work problems as regards Germany, upon which subject their assistance might be valuable … I would add that the matter has been discussed with Sir A[lexander] Cadogan [the permanent undersecretary of the Foreign Office], who concurs that we cannot possibly divulge our innermost secrets at this stage, but that if the Americans return to the charge, it might become necessary to refer the question of policy to the Prime Minister.

  ‘Y’ referred to the interception and direction-finding of enemy signals and to the decryption of low-level tactical and field codes, and most definitely did not include the ‘innermost secret’ of the Enigma. It was not until after the four American cryptanalysts – Abraham Sinkov and Leo Rosen from the Army, and Prescott Currier and Robert Weeks of the Navy – had been in the country three weeks that a decision was finally made to reveal to them that the Enigma was in the process of being broken and the methods that were being used. A memorandum from ‘C’ to Churchill dated 26 February 1941, reported that the British Chiefs of Staff ‘on balance’ now favoured ‘revealing to our American colleagues the progress which we have made in probing the German Armed Force cryptography’. But ‘C’ assured the Prime Minister that the discussions would be on technical aspects of cryptanalysis only and would not extend to ‘the results’, i.e., actual intelligence derived from Enigma traffic. A handwritten note from Churchill at the bottom of the memo reads ‘As proposed. WSC. 27.2’.

  On 3 March 1941, the Americans were informed of the British success against the Enigma. But there were strict limitations. A handwritten agreement dated that same day and signed by Weeks stated that they should inform no one of the information they had acquired, except the head of their section, Commander Safford, and him ‘by word of mouth only’. (The Army representatives agreed to a similar restriction.) The Americans would be given the wiring of the naval Enigma rotors, but agreed to ‘disclose that only when it is decided to work on the problem’.

  There has been considerable controversy in subsequent years ov
er the exact nature of the exchange of information that occurred during this visit. An account by Safford, written many years later, claimed that the Americans had been double-crossed; the United States gave the British its most closely held secrets about Japanese codes, even supplying a copy of the Japanese Purple machine that the US Army cryptanalysts had reconstructed, while the British gave the Americans nothing in return.

  But the true situation was more complex. Co-operation on Japanese codes began almost immediately and was definitely a two-way street. Even while the Sinkov mission was at GC&CS, the British cipher unit in Singapore received radioed orders to begin sharing information on JN-25 with the US Navy’s intercept and decrypting unit at Cavite in the Philippines, known as Station Cast. In February 1941, the two bureaux in the Far East exchanged liaison officers and thereafter regularly sent each other recovered code groups. (By June 1941 only about 1,100 code groups of the 55,000 used in the new JN-25B codebook had been identified between the two units, and these were mostly groups that stood for numbers and other mundane and common words or symbols that yielded little of intelligence value. By the time of Pearl Harbor the total of recovered groups was still under 4,000, and a change on 1 August in the additive book used to conceal the code groups’ identities in actual messages further blocked attempts to read traffic. At the time of Pearl Harbor not a single JN-25 message had ever been read currently, and since the December 1940 codebook change no JN-25 messages had yielded more than fragments, of no intelligence value.)

  Co-operation between the British and American codebreakers, in the true sense of the word, also began on German diplomatic codes. On Enigma, however, the British drew a careful line between ‘research’ and ‘exploitation’. It was one thing to have a technical discussion about cryptanalytic theory; it was quite another to let anyone else in on the actual intelligence operation – the system that transformed intercepted German military communications into military intelligence. The Americans were told about the Enigma and were shown the bombes, the electro-mechanical devices Bletchley Park had developed to recover the daily Enigma settings. But the visitors were not permitted to take notes, nor was GC&CS terribly quick in replying to subsequent requests for further details. On 15 July 1941, Washington requested information about daily Enigma settings; a month later the material ‘was still being copied’. Denniston was meanwhile ‘aghast’ to receive a letter from the United States asking for a copy of the bombe, explaining that ‘we avoid as far as possible putting anything on paper on this subject’.