The Secret War: Spies, Codes and Guerrillas 1939–1945

The impetus towards success was provided by a series of captures far out on the ocean, which dramatically increased Bletchley’s knowledge of the enemy’s naval communications. On 23 February 1941, British commandos raiding the Lofoten Islands seized the German armed trawler Krebs, from which spare rotors for a naval Enigma were recovered, though the machine itself had been thrown overboard. This ‘pinch’ prompted the Royal Navy to launch an operation explicitly designed to capture more Enigma material, targeting German weather-reporting trawlers between Iceland and Jan Mayen Island. On 7 May, a sweep by three cruisers located and seized the München – but too late to save its Enigma and associated coding data from the Arctic deep. On 25 June the navy caught its sister vessel the Lauenburg, again minus its Enigma, but with a useful haul of cipher material.

Hut 8 now had enough information to read some U-boat signals, but the seizure which opened the traffic to fluent decryption was the fruit of chance and high courage, rather than of design. On 9 May 1941 a convoy escort group attacked and forced to the surface Julius Lempe’s U-110. A boarding party from HMS Bulldog commanded by Sub-Lieutenant David Balme secured the submarine, prevented its sinking, and brought back to his destroyer pearls beyond price: documentation for current Enigma. Though U-110 later sank under tow – fortunately so, from a security viewpoint – the short signal book, officer ciphering instructions and other material reached Bletchley safely, and the secret of the submarine’s capture was preserved beyond the war’s end. An Enigma machine was also recovered, but perversely this was the least useful element of the booty, because Bletchley had one already, together with assorted rotors seized in other ‘pinches’. Within days, Hut 8 was reading a steady stream of German naval messages. Ralph Erskine, one of the foremost experts on codebreaking at Bletchley, believes that the Park was already close to reading the Kriegsmarine traffic, even without the U-110 haul. What is for certain, however, is that it was impossible to break the U-boat ciphers without the assistance of captured material, which would again become a vital issue later in the war.

The breakthrough into the Kriegsmarine ciphers came just too late to influence the pursuit of the Bismarck in the latter days of May 1941. Conventional direction-finding on the behemoth’s wireless transmissions, supported by air reconnaissance, were the key factors in enabling the Royal Navy to intercept and sink it on the morning of the 27th, though assisted in the last stage by decryption of a Luftwaffe signal revealing Brest as Bismarck’s destination. Thereafter, Bletchley produced a steady stream of messages that revealed U-boat positions and intended courses. The so-called Hydra cipher was laid bare, and other keys were progressively broken: the more the Park knew, the more it was able to discover. The flow of decrypts was never assured, however, and disturbing delays sometimes took place. ‘Huff-Duff’ – High-Frequency Direction-Finding – played an important secondary role in the location of U-boats. The outcome was a relentless shift in the balance of advantage in the Battle of the Atlantic through 1941 and into 1942. Here was a case where intelligence indisputably and importantly influenced events.

Bletchley was also reading a significant portion of Italian naval traffic. On 25 March 1941, one of the small number of women decrypters, nineteen-year-old mathematician Mavis Lever in Dillwyn Knox’s team – he was famously supportive of talented girls in a male-dominated institution – played a critical role in breaking a message which revealed that the Italian fleet would shortly put to sea to attack British convoys. The warning enabled the Mediterranean C-in-C Admiral Sir Andrew Cunningham to contrive an encounter off Cape Matapan during the afternoon and night of 28 March which ended in a striking victory for the Royal Navy. By dawn on the 29th, three cruisers and two destroyers had been sunk, while the battleship Vittorio Veneto was damaged, an outcome that deterred the Italian surface fleet from making any further attempt to interdict British troop movements to Greece.

Spring brought an increasing flow of decrypts about Wehrmacht operations in the Eastern Mediterranean. Senior officers strove to streamline the transfer of information from Bletchley to battlefields, so that material reached commanders in real time. One of the most significant intercepts, detailing German plans for the May 1941 invasion of Crete, reported ‘probable date of ending preparations: 17/5. Proposed course of operation … Sharp attack against enemy air force, military camps and A/A positions … Troops of Fliegerkorps XI: parachute landing to occupy Maleme, Candia and Retiomo; transfer of dive-bombers and fighters to Maleme and Candia; air-landing operations by remainder of Fliegerkorps XI; sea-transport of flak units, further army elements and supplies.’ Churchill personally annotated the flimsy: ‘In view of the gt importance of this I shd like the actual text transmitted by MOST SECRET together with warnings about absolute secrecy.’ This information was passed to Wavell and Freyberg, the relevant commanders, at 2340 on 6 May. The loss of the subsequent Battle of Crete, following the German invasion which began on the morning of the 20th, emphasised a fundamental reality about Enigma decrypts: they could change outcomes only when British commanders and troops on the ground were sufficiently strong, competent and courageous effectively to exploit them. Stuart Milner-Barry of Hut 6 said that he and his colleagues looked back on Crete as ‘the greatest disappointment of the war. It seemed a near certainty that, with … every detail of the operation spelt out for us in advance … the attack would be ignominiously thrown back.’

The Cretan signal, informing British generals of German intentions in time to respond, was an exception rather than a commonplace in 1941. Bletchley was able to provide an ever-growing flow of information about the deployments of the enemy, not least in Eastern Europe, most of it derived from Luftwaffe and army-Luftwaffe decrypts. Wehrmacht traffic stubbornly resisted penetration, but German railway codes provided information about – for instance – troop movements to Yugoslavia, Greece and Eastern Europe in the summer of 1941. Hitler’s looming invasion of the Soviet Union, the towering event of the war, was also the first great strategic development for which Ultra intelligence provided explicit warning. While Britain had no power to influence or impede Hitler’s Operation ‘Barbarossa’, it was clearly of the highest importance to Churchill and his generals to be able to monitor its unfolding.

It became a source of increasing frustration to the prime minister that British troops in North Africa failed to frustrate or defeat Rommel when they had not only superiority in men, tanks and guns, but also an ever-growing stream of information about German deployments and movements, for instance at Halfaya Pass in May. Churchill pored intently over his own daily file of Ultra material. When he read a decrypt reporting petrol stocks at various Luftwaffe airfields in Libya, he scrawled on it in his red ink: ‘CAS [Chief of Air Staff] How many hours flying can their a/c do on this – about? WSC.’ Air Chief Marshal Sir Charles Portal responded testily: ‘Unfortunately it is not possible to make any general deduction since the figures only relate to the stock at Benghazi. We do not possess complete figures for the supply and consumption of oil and petrol throughout Libya. All we know is that there are indications of an overall shortage which is limiting operations in the forward area.’ This problem was endemic when decrypts were fragmentary. Stewart Menzies performed an important service by dissuading the prime minister from fulfilling his frequent desire to dispatch raw Ultra direct to commanders-in-chief in the field, as he had done in the case of Crete. ‘C’ was surely correct, on security grounds, and also because decrypts that lacked the context of other intelligence could be highly misleading to untrained eyes.

On land, in 1941 Bletchley provided more guidance to strategy than to tactics: it gave Churchill’s high command an authoritative, though never comprehensive, picture of German deployments in every theatre of war. Ultra could do little to assist the RAF’s ongoing struggle with the Luftwaffe for mastery of the skies. Only the Royal Navy gained immediate advantage, both in the Mediterranean and the Atlantic. Nothing altered the fact that, until the worldwide balance of strength began to shift in the Allies’ favour in the latter part of 1942, the operational superiority of German and Japanese forces enabled them to keep winning victories. Bletchley was an increasingly important weapon, but it was not a magic sword.

The practices and disciplines of GC&CS evolved progressively, with many wrangles and turf wars along the way. Deputy director Nigel de Grey complained about the ‘very low standards of military behaviour’ prevailing in what was supposed to be a military establishment. But how could it be otherwise? Noel Annan wrote: ‘Many of the cryptanalysts who produced Ultra were agnostic, heterodox dons who did not set much store by the normal interpretations of patriotism and democracy.’ It was not easy to combine the discipline essential to the operation’s smooth functioning with sensitivity to the wayward and frankly eccentric character of some of its resident geniuses. Col. Tiltman wrote ruefully on 2 March 1941: ‘Cryptanalysts have to be handled delicately and do not take kindly to service methods of control, which are essential to the good working of signals.’ When the director of the Royal Navy’s women personnel visited the Park, she demanded indignantly: ‘Why are my Wrens working with civilians?’ WAAFs in the teleprinter room expressed resentment about taking orders from civilians. In December 1940 the War Office’s director of military intelligence staged a grab for Bletchley’s military output. Until 1941, the Admiralty tried to continue some cryptographic work under its own roof. In Hut 3, rows erupted between representatives of the three armed services. Stewart Menzies received a constant stream of complaints from rival interests, while Bletchley staff referred to Broadway without enthusiasm as ‘the other side’. One of the most durable criticisms of ‘C’ is that he was ever eager to accept credit for the achievements of the Park, while declining to engage with its chronic resource problems, which eventually prompted the October 1941 letter to Churchill signed by Turing and his colleagues pleading for more staff, that caused Churchill to send his famous ‘Action This Day’ message: ‘Make sure they have all they want on extreme priority.’ It is a serious charge against Menzies, that he was an absentee landlord of GC&CS.

Yet all this made mercifully little impact on the work of the codebreakers. Edward Thomas, a naval officer who worked at the Park, was impressed by the absence of hierarchical distinctions: ‘Despite the high tension of much of the work … anyone of whatever rank or degree could approach anyone else, however venerable, with any idea or suggestion, however crazy.’ Few people of any rank or status felt denied a voice – an unusually rare and privileged state of affairs in the wartime institutions of any nation. From 1941, the Cambridge scientist and novelist C.P. Snow became a key Whitehall intermediary, responsible for channelling suitable mathematicians and other scholars to Bletchley. GC&CS also employed thousands of humbler folk, recruited chiefly for their language skills. Its files record details of some RAF personnel interviewed, such as Leading Aircraftsman Berry, aged twenty-three, who had started training as a pilot but re-mustered owing to his conscientious objections to dropping bombs. His German language skills were graded only ‘B’, and the recruiters noted: ‘if interested in work might do well, but needs careful handling’.

LAC Gray was also ex-aircrew, ‘grounded as result of crash’, had ‘B’ grade Spanish. Cpl Hodges, aged twenty-six, was unfit for aircrew, ‘anxious to use his German “A”, in civil life worked in architect’s office’. AC1 Tew, a twenty-eight-year-old clerk, had German ‘A’, as well as some Spanish, French and Danish, acquired while working in his father’s leather-trading business. There was much snapping between Bletchley and the Air Ministry about the latter’s reluctance to grant commissioned rank to RAF men seconded to cipher or wireless interception duties. Group-Captain Blandy of the Y Service complained that such people were ‘picked individuals having considerable linguistic qualifications and a high standard of education … [Mere Aircraftsmen] and NCOs lack the necessary authority required to carry out their duties efficiently.’

Not all the personnel posted to Bletchley proved suited to its demands. A March 1941 report on an RAF officer returned to general duties after a spell at BP noted: ‘Although an excellent linguist, he does not appear to me to have any aptitude or inclination for the research side of the work. He had been relegated to clerical tasks, but did not seem thus to justify his pay.’ There were equally bleak verdicts on the performance of some women staffers lower down the hierarchy: ‘Wren Kenwick is inaccurate, very slow and not a bit keen on her work, not very intelligent. Wrens Buchanan and Ford are unintelligent and slow and seem unable to learn. Wren Rogers suffers from mild claustrophobia and cannot work in a windowless room.’ The report concluded: ‘The remainder … are doing most excellent work,’ but the selectors were urged to recognise the importance of the jobs the women were required to fulfil, ‘and not to send us too many of the Cook and Messenger type’.

Enfolded within their oppressive security blanket, Bletchley’s people lived, loved and largely played within their own community. Almost all were paid a pittance: nineteen-year-old mathematician Mavis Lever, one of ‘Dilly’ Knox’s team, initially received thirty shillings a week, of which she paid twenty-one shillings for her lodgings. When staff did escape into the world beyond the perimeter fence, the civilian status of the young men incurred dark suspicions among the uninitiated about their absence from any battlefield. The dramas and pantomimes performed by the Park’s amateur dramatic society became high spots in the annual calendar: Frank Birch, formerly of King’s College, Cambridge and now head of Hut 4, was celebrated for his appearances as the Widow Twankey in productions of the pantomime Aladdin.

By 1942, common sense had achieved some important successes in the Park’s management. Each section worked to its appointed head, irrespective of rank or lack of it. Cryptanalysis for all Britain’s armed forces was handled entirely at Bletchley and its Indian out-stations, a concentration of effort that neither Germany nor the United States ever matched. Gordon Welchman emerged as the foremost lubricator, curbing feuding; several notoriously stupid service officers were transferred out; the popular Eric Jones was appointed to head Hut 3. It was acknowledged that the civilian codebreakers must be ridden on the lightest possible rein, though the director was prone to occasional surges of authoritarianism.

On 1 February 1942, Admiral Karl Dönitz introduced a reflector or fourth rotor into the Atlantic U-boat service’s Enigma, with immediate and calamitous results for Allied fortunes in the Battle of the Atlantic: this imposed a twenty-six-fold increase in the range of possible settings, and blinded Bletchley. Sinkings soared. At sea, the Royal Navy was obliged to rely upon ‘Huff-Duff’ to locate enemy submarines until these approached within range of underwater detection by the Asdics of convoy escorts, which were impotent against night surface attackers. Breaking what was now designated the ‘Shark’ submarine key became the Park’s foremost priority, a challenge unresolved for nine frightening months, by far the most stressful period of the war for those engaged in the task. They knew, as they sat hunched over their labours in those austere huts, that at sea men were dying every day because of their failure – though no rational person would have called it such.

Also on 1 February, coincidentally, Alastair Denniston was pushed aside into a subordinate London role, to be replaced by his deputy, Edward Travis. In some measure this development reflected a clash of personalities – Denniston and Stewart Menzies disliked each other – together with the infighting characteristic of any large bureaucracy. But it was widely felt at Bletchley that its operational head was being overwhelmed by the strains of running an establishment that since the outbreak of war had increased fourfold in size, and many times that much in its importance to the war effort. Power struggles were unavoidable. Denniston was a good and kind man who had done many things well, but Bletchley had outgrown him. Travis, whose edicts were issued in a curious trademark brown ink, was generally considered a success in his new role, not least by such influential creative figures as Welchman. When another codebreaker, Ralph Bennett, returned that summer from detached duty in the Middle East, he found that the atmosphere had changed markedly: ‘I had left as one of a group of enthusiastic amateurs. I returned to a professional organisation with standards and an acknowledged reputation to maintain. Success was no longer an occasional prize, but the natural reward of relentless attention to detail.’

Throughout 1942, Bletchley’s activities were hampered by a desperate shortage of bombes, and thus by argument about their best employment. In January the army-Luftwaffe Hut 6 was receiving 1,400 intercepts a day, of which an average of 580 were broken, a proportion that slowly increased, reaching about 50 per cent by May 1943. Often no more than one three-wheel bombe was available at any given time to work on the Shark U-boat cipher, because the others of what was still only a handful of machines were committed to breaking army and air traffic. The codebreakers said later that they would have needed ten four-wheel bombes – which did not then exist – significantly to accelerate their progress. By November, a note of desperation had entered the Admiralty’s pleas to the Park about Shark. The Battle of the Atlantic, said the navy’s Operational Intelligence Centre, was ‘the one campaign which BP are not at present influencing to any marked extent – and it is the only one in which the war can be lost unless BP do help’. A critical breakthrough was imminent, however. On 30 October in the Eastern Mediterranean U-559 was attacked by an escort group, and forced to the surface by depth-charging. Tony Fasson, thirty-year-old first lieutenant of the destroyer Petard, along with Able Seaman Colin Grazier, hastily stripped naked and swam sixty yards to the stricken submarine, then hauled themselves into the conning tower. The crew had opened the seacocks before abandoning their boat, and the sea was flooding in even as the two men searched the control room with desperate urgency.

They found treasure: the second edition of the Wetterkurzschlüssel, or weather short signal book, for its Enigma. Having wrapped this and other documents in waterproofing, Fasson and Grazier handed them up the hatch to sixteen-year-old NAAFI canteen assistant Tommy Brown, who had followed in swimming to the U-boat. He in turn passed the packages to the crew of a whaleboat, which arrived alongside in the nick of time. Brown, a civilian, lived to receive a George Medal for his daring, but the two supremely dedicated British sailors pushed their luck by plunging once more into the submarine’s control room, possibly in the belief that that they might retrieve a cipher machine. Bletchley did not need this, for it had already reconstructed the wiring of a four-rotor Enigma: it was the signal books that mattered. U-559 suddenly vanished into the Mediterranean, taking with it Fasson and Grazier, both of whom received posthumous George Crosses. The captured documents reached Bletchley on 24 November, and made possible the critical break into the Shark key on 13 December, assisted by data from weather decrypts secured by Hut 10.

That day, the codebreakers teleprinted to the Admiralty’s Operational Intelligence Centre locations for twelve Atlantic U-boats. Their positions were by now a week out of date, but they sufficed to provide critical guidance about the Germans’ likely courses. Thereafter, Shark signals were frequently broken within twenty-four hours, though the delay sometimes extended to forty-eight. This was one of the indisputably decisive moments of the intelligence war. Once regular Shark decrypts began to flow through to the Royal Navy, the balance in the war at sea shifted dramatically. Though Hut 8 later suffered more delays and difficulties with Shark, never thereafter was British control of the Atlantic sea route seriously threatened, and U-boat sinkings soared.

Among much else remarkable about Bletchley were not its periodic rows and tantrums, but that the front-line codebreakers, whose average age was twenty-three, sustained such a degree of fellowship. Derek Taunt described how they felt ‘devoted to the task of outwitting the enemy and happy to be part of a complicated organization designed to do just that’. Rolf Noskwith paid tribute to what he described as the Huts’ ‘exemplary leadership’. The integrity of the decoding operation was much assisted by the personal friendship between Stuart Milner-Barry of Hut 6 and Hugh Alexander of Hut 8. But tranquillity could never be attainable when thousands of men and women were working under appalling pressure around the clock, month upon month, year after year, knowing that lives depended upon their efforts. On 15 May 1943 Welchman wrote to Nigel de Grey, apologising for an explosion of rage during a discussion about organisation and shortage of resources, an ongoing bugbear. ‘My touchiness,’ he wrote, ‘is probably due to the fact that I always have the extreme value and urgency of our work very much on my mind. Throughout the whole history of Hut 6 there has never been a time at which I felt that we were being as efficient as we could be and you can imagine that this has been a heavy and continual strain … The present situation is an absolute scandal, but there is nothing we lack now that has not been asked for again and again. So please forgive me for being somewhat bitter and ill-tempered.’

He added: ‘A great deal of the work is terribly monotonous and deadly dull, and this has a very serious effect on morale over a long period. Some of the girls are almost physically sick at the sight of a Type-X machine. Now, if our girls crack up as many have done, we are absolutely sunk, and no amount of belated assistance will save us … Incidentally, could you possibly persuade Travis to get [Air-Marshal Charles] Medhurst [RAF director of intelligence] and [the CIGS Gen. Sir Alan] Brooke to spend even one minute telling the girls that their work is important? Yours ever Gordon.’ But difficulties persisted in securing qualified personnel, not least because so few people in Whitehall had any inkling of the supreme priority of GC&CS’s work. When BP needed personnel to operate punch-card machines, its recruiters turned to employees of the John Lewis Partnership, the department-store chain which had personnel trained to use them. Astoundingly, after ten women had been selected, the Ministry of Labour insisted that they should instead be dispatched to do land work. An internal memo at the Park seethed: ‘The John Lewis episode is a disgrace.’ The girls were eventually released to GC&CS, but only after a bitter wrangle with the civil bureaucracy.

From the war’s first day to its last, security was an obsession of every Allied officer privy to the Ultra secret. In 1941 a certain Col. Gribble, who had served as an air liaison officer with the RAF in France in 1940, published a book entitled Diary of a Staff Officer, which caused near-hysteria when Whitehall noticed, because it contained references to unidentified ‘secret sources’. Gribble’s work had been passed by a censor who knew nothing of Bletchley Park. What if somebody in Berlin read it, and drew lethal inferences about the vulnerability of Germany’s ciphers? MI5 bought up and pulped 7,000 unsold copies of the book, trusting to luck that none of its existing buyers had German friends. Before the fall of Singapore in February 1942, the key local Ultra and Y Service personnel received priority for evacuation, as did their American counterparts on Corregidor two months later. Had they fallen into captivity, not only would they have suffered a ghastly fate alongside other British and Australian prisoners, and their rare skills have been lost, but the risk to Allied codebreaking was frightening if they were exposed to interrogation and torture.