GCHQ

By early 1941, the flow of material from the breaking of Enigma was impressive. The intelligence from Bletchley Park was circulated on a very select basis, and was marked with the code word ‘Ultra’ to denote the extremely high level of security attached to the material. Menzies showcased his triumph by taking senior figures from Whitehall on day trips to Bletchley Park. On 11 January it was the turn of Alexander Cadogan. He noted in his diary:

Cold but thawing. Had a rush at the FO till 11, when I left with Menzies for Bletchley. Got there about 12.30. Very Interesting – I should like to spend a week there so as to try and understand it. A charming young Cambridge professor of geometry – Welshman [Gordon Welchman] – did his best with me. A good show, I think.³²

Others soon made the pilgrimage to the strange mock-Tudor mansion surrounded by temporary huts. On 6 September 1941 Winston Churchill himself, now Prime Minister, stood on a pile of bricks left by some workmen alongside Hut Six and gave an impromptu speech – delivered with deep emotion – about the value of Bletchley Park to the war effort.³³

Unbeknown to Churchill, Bletchley Park was in deep crisis. This was partly due to its rapid growth, and partly to the uncertain institutional boundaries that were evolving almost daily. The situation was exacerbated by a complex relationship with the ‘Y services’, the lower-order radio intercept organisations run by the Army, Navy and Air Force that fed Bletchley with captured traffic. Meanwhile the three armed services were themselves vying for increased control over who received the output from GC&CS. This was precisely the kind of complex organisational puzzle that Menzies was ill-equipped to deal with. Matters reached a head in the autumn of 1941, forcing Menzies to appoint a Joint Committee of Control, which included members of both SIS and GC&CS. However, as the historian Philip Davies observes, ‘Like so many of Menzies’ administrative initiatives, the committee proved unequal to the task.’³⁴ There was also a general resources problem. Having made significant inroads into German Enigma traffic, there were simply not enough staff at Bletchley Park to process the vast torrents of accessible German communications. Neither Alastair Denniston nor his deputy, Edward Travis, had the pull in Whitehall to overcome the shortage.³⁵

Churchill was not ignorant of this state of affairs for long. Recalling the Prime Minister’s kind words during his recent visit, the code-breakers resolved to go straight to the top. On 21 October 1941, four of the most brilliant minds at Bletchley Park, Hugh Alexander, Stuart Milner-Barry, Alan Turing and Gordon Welchman, wrote directly to Churchill to beg for more resources, explaining that their work was so secret that it was hard to explain their requirements to those who controlled personnel.³⁶ So secret was their missive that Milner-Barry took the train to London and delivered it personally to 10 Downing Street. Churchill was shocked by these revelations, and demanded ‘Action This Day’. He ordered his military assistant, General Hastings ‘Pug’ Ismay, to ensure that GC&CS had everything it needed, and to report that this had been done.³⁷ As a result, Bletchley Park underwent a further expansion, and more importantly a major reorganisation.³⁸

GC&CS was now divided into two distinct parts, civil and military. The end of the Blitz meant that the civil side, which dealt with economic and diplomatic traffic, could be sent back to London with relative safety. It took up residence in Berkeley Street, partly because the work of attacking diplomatic codes often had to be coordinated with discreet telephone taps on the foreign embassies in London. The military side remained at Bletchley Park. This did not resolve the heated arguments about who controlled the spoils of GC&CS, but it did address the immediate accommodation problems, and created two organisations of a more manageable size. Menzies retained his post as overall Director, but was a notably absentee landlord. Alastair Denniston was sent to London as Deputy Director (Civil), while his talented deputy, Commander Edward Travis, remained at Bletchley as Deputy Director (Services).³⁹ Travis was now the rising star.⁴⁰

British code-breaking in the early years of the war was not just about the German military secrets revealed through Enigma. Even harder to break than the Enigma machine had been a German teleprinter on-line cypher machine known as ‘Tunny’, used by the German High Command to produce ‘Fish’ messages. On-line cypher machines were especially challenging because they were automatic, and sent a continuous stream of text, much of it dummy material, sometimes offering no obvious start or end points to each message. This went some way to eliminating another weakness of the Enigma machine – its operators, who were prone to human error. To address the problem of ‘Tunny’, the British later built ‘Colossus’, one of the earliest general-purpose electronic machines, and perhaps the first device that might be described as a ‘computer’. Conceived by Professor Max Newman and then developed by Tommy Flowers from the British Post Office research facility at Dollis Hill, this was one of the supreme technical achievements of the war.⁴¹

The achievements of the civil side of GC&CS have often been neglected. By 1940 it was analysing not only the diplomatic codes and cyphers of the Axis powers, but also those of more than twenty other countries. These included the Soviet Union, which did not enter the war until it was attacked by Germany on 22 June 1941. The diplomatic communications of quarrelsome allies such as the Free French, or important neutrals such as the Turks and the Spanish, proved as interesting and as useful as those of Germany. Moreover, the traffic of Germany’s allies, such as Japan, could shed a penetrating light on the mindset of Berlin. Throughout 1941 Hitler held regular meetings with Baron Oshima, the Japanese Ambassador in Berlin, often referred to as ‘Hitler’s Japanese confidant’. Japan had its own complex cypher, known as ‘Magic’, produced by a machine called ‘Purple’, and Oshima used it to send detailed accounts of his long conversations with Hitler to Tokyo. ‘Magic’ had been broken by the Americans, and early Anglo–American cooperation on code-breaking ensured that all this was being read in London. Remarkably, Berkeley Street was also working on the cyphers of the United States, which did not join the war until the Japanese attack on Pearl Harbor on 7 December 1941.⁴²

The dramatic events of 1941 transformed the course of the Second World War. Although the Battle of Britain had staved off the possibility of a German invasion, by the summer of 1941 Britain had been fighting for almost two years without a major victory. Therefore, Hitler’s bizarre decision to invade Russia in June 1941, which required the legions of the Wehrmacht to turn east, provided a welcome breathing space. After Japan’s attack on Pearl Harbor, Britain, the United States and Russia found themselves ranged together against the Axis in what was soon called the ‘Grand Alliance’. Welcome as this was, a genuine world war created new dilemmas for the denizens of Bletchley Park, who now confronted the ticklish issue of large-scale Allied cooperation in the business of code-breaking.

2 Friends and Allies

…there is no better analogy than the schoolboy with his stamp collection.

GC&CS, discussing intelligence cooperation with the Russians in 1943¹

The most secret aspect of Bletchley Park’s wartime work was its dealings with friends and allies. Many have pondered whether the British attacked Soviet codes and cyphers during the Second World War. The official history of British intelligence insists that Churchill ordered this activity to stop in June 1941, following Hitler’s invasion of the Soviet Union, since Moscow had suddenly become an ally.² However, it is now clear that this is quite untrue. At the end of October 1941, intelligence chiefs were actually discussing the expansion of the sigint organisation in India, which was then dealing with ‘material from Russian, Persian and Afghan sources’. Remarkably, it was not yet working on German traffic.³ Moreover, in January 1942, and again in early 1943, the British and the Americans were discussing the mutual exchange of intercepted material from ‘Slavic nations’.⁴ Soviet cyphers had been the core business for Britain’s interwar code-breakers, and work on this material never stopped completely during the Second World War.

To understand why, we must cast our minds back to the approach of the war. During the 1930s, GC&CS continued to follow the traffic of the Comintern even after other Soviet systems were lost. This revealed persistent efforts to subvert the British Empire in locations such as India, Malaya and Hong Kong. Indeed, the Soviet Union appeared to be in league with Germany after the Nazi–Soviet Pact of August 1939. It is often forgotten that Poland was invaded by Germany and the Soviet Union together. For a nightmare period between August 1939 and June 1941, many suspected that Germany, Italy, Japan and the Soviet Union would act in uneasy concert, dividing the spoils of the world between them. This was precisely the plan that Germany’s Foreign Minister, Baron Joachim von Ribbentrop, was trying to press upon his irascible master. However, in the end Adolf Hitler’s racist outlook could not tolerate the idea of alliance with the Slavic peoples, and he had always declared his desire for ‘Lebensraum’ in the east.⁵

Throughout this dangerous period, before Hitler and Stalin turned upon each other, the Soviet Union remained a key intelligence target. SIS even organised a secret squadron to conduct aerial reconnaissance of possible bombing targets deep inside southern Russia, notably the oilfields. GC&CS developed close relations with code-breakers in the Baltic states who were also working on Soviet codes. A month after the outbreak of war with Germany, Clive Loehnis, a naval officer at GC&CS (who would become Director of GCHQ in the 1960s), told Alastair Denniston that additional premises were needed to cope with the increase in the interception of Soviet military traffic, so new buildings were erected at Scarborough.⁶ With the military chiefs keen to ‘get cracking on Russian traffic’, Denniston began a unique and profitable experiment. In 1939 GC&CS sent a party of British sigint operators to Sweden to work secretly out of the British Embassy in Stockholm, where there was better radio reception from Russia. The creation of this forward listening station was fortuitous, since Stalin embarked on the Winter War against Finland in November 1939, and GC&CS enjoyed a front-seat view of the whole proceedings.⁷

John Tiltman remained the key figure in the effort against Soviet communications. A colonel in the King’s Own Scottish Borderers, he was noted for his smart uniform, which included tartan trews. However, as the war progressed he came under the influence of the spirit of Bletchley Park, and was often seen in a baggy pullover and green corduroy slacks.⁸ One of his first duties was to visit Helsinki to conclude a deal with the talented Finnish code-breakers. Britain funded the expansion of the Finnish cryptographic bureau, and supplied it with the latest equipment in return for material on the Soviets. In March 1940, after imposing a series of humiliating defeats on the Soviets, the Finns signed the Moscow Peace Treaty, ceding about a tenth of their territory.⁹ The sigint deal with the British was unaffected, and indeed in September 1940 its scope was expanded during a visit by Admiral Godfrey, the Director of Naval Intelligence. According to an internal GC&CS history written after the war, ‘The Finns had agreed to supply us with copies of all their intercepts and cryptographic successes, provided that we did the same.’ Preceding the agreement with the Americans by more than a year, this was perhaps Britain’s first comprehensive sigint alliance.¹⁰

By March 1940, the interception of Soviet traffic was big business. For the first time, collection began in the Middle East, at Sarafand in Palestine, although it was still sent to India for analysis. Soviet traffic was also being taken at Ismailia in Egypt and Dingli in Malta. Meanwhile, in Hong Kong, other British sigint operators were also listening to the Soviets before they packed up their equipment to move to Singapore in anticipation of a Japanese attack. The surge of Soviet traffic meant changes were required at GC&CS, where an inter-service Soviet section was created to work in close conjunction on naval, military, air, diplomatic and commercial material. After the fall of France in the summer of 1940, evacuated French cryptographers joined the effort on Soviet traffic at GC&CS. A Polish section, based at Stanmore on the northern fringes of London, soon discovered that it was able to listen in to Soviet traffic as far away as Ukraine.¹¹

Ultra had provided Bletchley Park with an intimate picture of the build-up of German forces in the east, prior to their attack on the Soviet Union. As early as January 1941 it was clear that Hitler’s vast armies were being moved eastwards in preparation for some grand project. Yet even with the evidence of many German divisions massing in the east, Whitehall refused to believe that Hitler was mad enough to deliberately opt for war on two fronts. Like Stalin himself, the British Chiefs of Staff believed that this was more likely to be a prelude to a German ultimatum, a bluff in which Hitler would demand the cession of some further territory in Eastern Europe. Throughout early 1941, Stalin believed that all war warnings were self-serving efforts at deception by the West, which sought to provoke a war between Germany and the Soviet Union. Stalin has frequently been ridiculed for ignoring the warning signs of the impending attack, but despite the benefits of Ultra, it was only the month before the fateful date of 22 June 1941 that British intelligence chiefs realised what was about to occur.¹²

Hitler’s decision to turn east was a fabulous stroke of luck for Britain. At a time when its forces were struggling, this was a most welcome redirection of the main German war effort. Taken together with Pearl Harbor at the end of the year, it is right to regard 1941 as nothing less than the fulcrum of the war. However, Bletchley Park now faced a new problem. Should it pass sensitive intelligence derived from Ultra to the new Soviet ally, which had been a dedicated enemy of Britain since 1917? The idea that two of Britain’s adversaries were about to fight to the death filled most military intelligence officers with ill-disguised glee. Many argued that passing sigint to the Soviets was pointless, since few expected them to hold out later than 1942. Others insisted that not even Ultra could penetrate the fog of self-deception with which Stalin had surrounded himself.¹³

In the event, Bletchley Park did develop a precarious sigint liaison with the Soviets. When the British Chiefs of Staff despatched a military mission to Moscow, the code-breakers decided to work through it to find out what the Soviets were doing. They began cautiously, asking about ‘low-grade material only’, notably German Air Force three-letter tactical codes. They intended to send an officer from Bletchley, and in the long term even hoped to persuade the Soviets to accept a British Y unit, or forward listening station, that would intercept German tactical messages on their front. In late 1941 the Soviets agreed to a visit from Squadron Leader G.R. Scott-Farnie, who worked on Britain’s Y interception system in the Middle East.¹⁴

Scott-Farnie gave the Soviets a good deal of information on low-grade German Air Force systems, but quickly came up against a different culture of intelligence exchange.¹⁵ The Soviets adored captured documents, and did not attach much credence to any information that was not supported by such evidence. Once the game of document exchange began, Scott-Farnie discovered that the Soviet approach ‘was precisely that of a horse dealer who enjoys the poste and riposte of a bargain, and they looked at the exchange of documents on an eye for an eye basis’.¹⁶

Bletchley now had to decide whether to follow up the Scott-Farnie Mission. Alastair Denniston was ‘full of hesitation because of the continued Soviet retreat before the German onslaught’, but the intelligence directorates of Britain’s three armed services thought it worthwhile. Josh Cooper, who had reviewed the exchanged material, concluded that the Soviets were ‘absolute beginners’ in their work on the German Air Force, but thought they should be shown the RAF Y stations at Kingsdown in Kent and Cheadle in Cheshire to point them in the right direction. If the Soviets were impressed, he added, they might allow a British Y unit to be sent to the Soviet Union.¹⁷ In the end, Edward Crankshaw, an Army Y Service officer, was sent out, armed with more barter material in the form of documents. This was to be ‘swapped’ with the Soviet interceptors, since Bletchley Park thought ‘there is no better analogy than the schoolboy with his stamp collection’. By the spring of 1942 Crankshaw was established in the Soviet Union, and was trading his wares.¹⁸ However, the greatest success in the Soviet Union was achieved by the Royal Navy. It was running supply convoys to the Russian port of Murmansk, and this justified the setting up of a radio station at the nearby town of Polyarnoe. A small naval Y intercept party was soon attached to it, and began cooperating with the Soviets on low-level German naval communications. This kept going until December 1944, and yielded good material on subjects such as the movements of the German battleship Tirpitz in northern waters.¹⁹

The main worry about giving Ultra to the Soviets was the insecurity of their own cyphers – in 1942, Bletchley Park was increasingly aware of the German ability to read a great deal of Soviet operational military traffic in the field. Frederick Winterbotham, who worked on sigint distribution, argued that Moscow simply had to be told about the weak security of its cyphers. However, Winterbotham’s colleagues insisted that it was ‘impossible’ to tell the Soviets, even though he had ‘invented a good cover story’ to explain how they knew.²⁰ The secret truth was that Bletchley Park was collecting second-hand sigint. The Germans were sending their own sigint from the Eastern Front back to Berlin using an Enigma key code-named ‘Mustard’, which in turn was being read by the British. Although much of the sigint obtained from the Soviets was operational, the British also noted that ‘first grade traffic can be read – at least in part’ by the Germans. Some of the German successes had stemmed from a Soviet codebook, ‘OKK–5’, known to have been captured by the Finns and given to the Germans. While the British had struggled to break these codes in the 1930s, the Germans were having more success.²¹ On 16 June 1942, Nigel de Grey, the Deputy Director at Bletchley Park, stepped in and settled the argument. He noted that Edward Crankshaw, the GC&CS liaison with the Soviets, would soon be returning from Moscow for another visit. He would be ordered to give the Soviets the details of their compromised cyphers and ‘the methods of reading’. This decision probably reflected the fact that, against all predictions, the Soviet forces were hanging on impressively and looked as if they were going to be in the war for some time to come.²²

In August 1942, Crankshaw briefed the Soviets on their appalling lack of security, typified by their alarming tendency to use low-grade cyphers for high-grade secrets.²³ There was abundant evidence of this in German Air Force Enigma, but Crankshaw only hinted at it by ‘somewhat tenuous means’. Predictably, the Soviets would not accept his warnings because ‘direct evidence was not forthcoming’. Depressed, he went back to Bletchley Park in February 1943, never to return to Moscow. He joined the staff at Bletchley Park and tried to keep the relationship going at a distance, ‘but the temperature was falling’. The Director, Commander Edward Travis, was only willing to allow the relationship to continue ‘if it is a solid gain for us’. The Polyarnoe naval listening station continued to function, but with the Soviets turning the tide on the Eastern Front they seemed to feel no need for further cooperation, and other contacts ‘petered out’.²⁴ On 9 February 1944, London discussed the possibility of a visit to Britain by Soviet cypher experts and decided against it.²⁵

Bletchley Park’s heated debate on what information to give to the Soviets was academic. All along, one of the KGB’s top agents, John Cairncross, had been working at Bletchley. Although Cairncross studied at Cambridge in the early 1930s, he was not recruited by Anthony Blunt, one of the key KGB talent scouts there, who found him both quarrelsome and arrogant. Instead, after Cairncross joined the Foreign Office in 1936, he was persuaded to work for Soviet intelligence by James Klugman, a prominent British Communist, who later served in the wartime Special Operations Executive. Although Cairncross was fearsomely intelligent, his difficult personality ensured that he was always being moved on. At the outbreak of the war with Germany he was sent to the Cabinet Office to work for the Cabinet Secretary, Lord Hankey. There he saw some of the early British thinking on the development of the atomic bomb. In 1941 he was moved to Bletchley Park, labouring in Hut Three on the Luftwaffe order of battle. His moment of triumph came in early 1943 when he was able to warn his KGB controller of the impending German armoured offensive at Kursk. Code-named ‘Operation Citadel’, this was the last great German push on the Eastern Front. It proved to be the largest tank battle of the Second World War, and the information provided by Cairncross proved to be important in launching an early attack upon the German tactical air force, much of which was destroyed on the ground. Stalin later awarded him the Order of the Red Banner in recognition of his achievement.²⁶

Soon after Kursk, Cairncross moved again. He now returned to London and ended up in Section V, the counter-intelligence section of SIS, working alongside Kim Philby. Although he worked with Philby, Guy Burgess and indeed Donald Maclean, Cairncross was unaware of their common allegiance to Moscow, and believed he was the sole high-grade KGB agent in Whitehall. Bizarrely, he was caught in 1951 because of an official note in his handwriting found in the flat of Guy Burgess after Burgess had fled to Moscow with Maclean. Cairncross had given Burgess this quite innocently in the course of official business, without knowing he was a fellow spy. Once the note was found, Cairncross was followed, and MI5 surveillance believed they had caught him trying to meet with his KGB controller. Without hard evidence he could not be prosecuted, and he was merely asked to resign. Ironically, the Ultra material that Cairncross passed to the KGB was taken more seriously by Moscow precisely because it was stolen. Had the British handed it willingly to their ally, Stalin’s suspicious mind would almost certainly have devalued it.²⁷

Cairncross was not the only KGB agent with access to Ultra. In late 1942, Anthony Blunt, another high-grade Soviet agent, was designated one of the two MI5 liaison officers who worked closely with Bletchley Park.²⁸ Anxiety about KGB agents and subversion was yet another reason that the British kept working on Soviet traffic. Monitoring stations, notably the Metropolitan Police intercept station at Denmark Hill in south London, reported an upswing in traffic between Moscow and secret agents in Britain. There was also a British field unit, called the Radio Security Service, that hunted for illegal agent radio transmissions, and it told the same story, although the agent traffic could not be broken.²⁹ John Croft, who worked at the GC&CS diplomatic code-breaking centre at Berkeley Street in London, was one of those who soldiered on with Soviet material. Croft was engaged on wartime Comintern traffic in Europe, known as ‘Iscot’, which could be read. Although circulated only to a very select group of individuals within Whitehall, this material mostly revealed a dutiful Soviet struggle against their shared enemy, Nazi Germany. There is no indication that this material was exchanged with Washington.³⁰

Early British cooperation with the American code-breakers was also tentative. Again, the obstacle was obsessive security. Security problems existed on several different levels. The British and the Americans had cooperated on sigint during the First World War, but this had bequeathed a legacy of doubt and anxiety, even distrust. In November 1940, when reviving sigint cooperation with the Americans was discussed, Alastair Denniston was quick to point out that after the First World War the ‘notorious’ American code-breaker Herbert O. Yardley had published a tell-all book about his experiences. The very name ‘Yardley’ caused a shudder in British code-breaking circles. Yardley was now working for the Canadians, and GC&CS insisted that they sack him summarily before they were allowed to join the wartime sigint club.³¹ Indeed, the Canadians were told that other agencies ‘would not touch Yardley with a ten foot pole’.³²

The British, and especially Sir Stewart Menzies, the Chief of SIS, were frosty towards the Americans, and regarded them as fundamentally insecure. By contrast, the Americans generously opted to share the secret of their spectacular code-breaking success against the Japanese ‘Magic’ diplomatic cypher with the British as early as January 1941, even handing over precious examples of their copies of the Japanese cypher machine. The British were ‘flabbergasted’. They did not expect the Americans to ‘simply walk in and plonk down their most secret cryptanalytical machine’.³³ Yet the British remained reticent, and did not initially reciprocate fully with their knowledge of Enigma. The jibe about American insecurity had a certain irony, since the British chose to send one of the priceless American copies of the ‘Purple’ machine out to their naval base at Singapore shortly before it fell to the Japanese. The machine was delivered by ship just as the Japanese invasion of Malaya began, and disappeared into the chaos of battle. To this day its fate is unknown.³⁴

Collaboration with Washington was also hard because American sigint was a house divided. Although William Friedman, the US Army’s best cryptologist, was busy advocating sigint cooperation with the British in early 1940, the US Navy’s chief code-breaker, Commander Laurance Safford, was adamantly set against working with allies. But after pressure from President Franklin D. Roosevelt the Navy had been won round, and the Americans sent a team of technical experts to Britain in early 1941. Known as the ‘Sinkov Mission’, they spent several weeks touring Bletchley Park and visiting outlying intercept stations. The British were willing to receive them because they knew the main focus of American attention was Japan. At this stage the British were keen to keep discussions focused on Japan, because this allowed them to hide the extent of their knowledge of the German Enigma system. Both Sir Stewart Menzies and Sir Alexander Cadogan were adamant that the Ultra secret would not be shared with the Americans.³⁵ Laurance Safford later represented the first Anglo-American exchanges of late 1940 and early 1941 as a one-way street in which the Americans handed over their precious ‘Magic’ material on Japan but got nothing in return. In fact this is far from the case. Prescott Currier, one of the Americans who came to Bletchley in early 1941, recalled: ‘All of us were permitted to come and go freely and to visit and talk with anyone in any area that interested us.’³⁶ Later that year, a select circle of American code-breakers were also given more details about Enigma.³⁷

The hottest issue was the distribution of sigint to the policy-makers. In late May 1941, Brigadier Raymond Lee, the American Military Attaché in London, conveyed an American request for comprehensive intelligence exchange in the Far East. There followed painfully slow and complex discussions about who would get sigint with what levels of security: ‘The whole thing has been so tangled up,’ he complained.³⁸ Sigint was also very confused in Washington. Unlike Britain’s GC&CS, American signals intelligence was less centrally organised, resulting in great rivalry between the armed services.³⁹ Because the American wartime sigint organisation was divided between the Army and the Navy, one of the great problems for the British was cooperating with one without upsetting the other. Famously, the Americans solved the tussle over who would decrypt Japanese codes by agreeing that the Army would decode the material on the even days of the month, and the Navy on the odd days. A more ludicrous system for the division of labour would have been hard to devise.⁴⁰

GC&CS might have been more centralised than the Americans, but it had less money. Expanded cooperation with America on Japan allowed GC&CS to shed some difficult code-breaking tasks. High-grade Japanese Army cyphers had proved impenetrable for a decade. By 1941, Bletchley Park was too busy with the European war, while its Far Eastern code-breakers were struggling to cope with the mass of material on Japanese espionage derived from low-level consular intercepts in South-East Asia. On 22 August 1941, Anglo-American cooperation lifted this task from their shoulders. During talks in Washington, Alastair Denniston persuaded the US Army that it should ‘take over investigation of Japanese main army cipher soon as priority commitment’. Shortly after, Captain Geoffrey Stevens from Singapore travelled to Washington carrying all the British material on the Japanese main army cypher.⁴¹ The British were glad to see the back of it. At the end of the war approximately 2,500 Americans would still be working on this one Japanese cypher to no avail.