Tiltman, a brilliant major from the Indian Army who had been running a small but successful interception effort in north India during the 1920s. In 1929 he was brought back to London to lead an expanded operation against Comintern communications (which were code-named ‘Mask’). This allowed the British government to learn of the secret subsidies paid by Moscow to the Communist Party of Great Britain and its newspaper, the Daily Worker. It also contributed to important successes against major Comintern agents in imperial outposts and international centres such as Singapore and Shanghai.[12]
Faced with the real threat of active subversion throughout the British Empire by the Comintern, GC&CS paid limited attention to military matters or the rise of the Axis until the mid-1930s. Germany, Italy and Japan were a remarkably low priority. Admittedly, a small naval section of GC&CS had been set up in 1925, and its most important work was done overseas by naval officers like Eric Nave, based in Hong Kong. From here they had ample practice at following military operations, because of the extensive fighting in Manchuria during the 1930s. Italy’s attack on Abyssinia in 1936 provided a new target for British code-breakers in the Middle East, located at sites such as Habbaniya in Iraq and Sarafand in Palestine. Remarkably, and despite the growing importance of air power, GC&CS only developed an RAF section in 1936, under Josh Cooper, a young and talented code-breaker who had joined the organisation a decade earlier with a First in Russian from King’s College London.[13]
Cyphers were important to the Axis military powers. One-time pads were slow and cumbersome. Moreover, they were out of step with the emerging new methods of warfare. Blitzkrieg, for example, required armoured forces to move forward at lightning speed, coordinating their activities with artillery and air support. So the pressure was on to find a way of making the growing volume of military radio traffic unintelligible to the enemy. Most developed countries turned to cypher machines to make their immense volumes of traffic secure.[14] Complex cypher machines had been pioneered by banks and businesses – banks had long used fairly simple cyphers to keep commercial matters secret. In the 1920s, the German military adapted a Dutch invention to produce the Enigma cypher machine as an alternative to laborious hand cyphers. In fact, the first Enigma machines were sold commercially, and were widely used by banks and businesses. Enigma was what we now recognise as a ‘commercial off-the-shelf solution’ to a difficult military problem.[15]
The Enigma machine itself looked like an early typewriter in a square wooden box, but with a keyboard set out in alphabetical order rather than the traditional ‘QWERTY’ arrangement. As each letter key was depressed a set of lights that corresponded to the alphabet lit up, seemingly at random. The innovation was the rotors, which looked like fat metal wheels, embedded in the top of the machine. These rotated and scrambled the message in a highly unpredictable way. There were initially three – later four – rotors, with twenty-six positions relating to the letters of the alphabet. These moved round in a stepping motion that generated a cypher with an enormous number of possibilities. Moreover the complex nature of the rotation caused subtle changes in the stream of material, creating substantial headaches for any would-be code-breaker. The Germans were not alone in developing cypher machines. The British and Americans developed similar devices, respectively called the Typex and Sigaba.[16]
Critical to the breaking of Enigma was assistance from the secret services of France and Poland. French intelligence employed a lugubrious German agent called Hans Schmidt, who worked in the German military cypher department. Fond of the finer things in life, which the French secret service supplied to him in abundance, Schmidt divulged many technical documents about Enigma, including messages in both clear and encyphered text. He was later betrayed, and would commit suicide using cyanide procured for him by his daughter. By 1938 these secrets were being shared with the British through ‘Biffy’ Dunderdale, the SIS station chief in Paris. However, when the French gave the British material on German Air Force communications a further secret was accidentally revealed, namely that the French were also working on Enigma in collaboration with the Poles. In January 1939 Alastair Denniston took two of his top code-breakers, Hugh Foss and Dilly Knox, to Paris to meet their French and Polish opposite numbers. Eventually they discovered that the Poles had completely reconstructed the German version of the Enigma machine.[17]
Remarkably, by 1938 the Polish code-breakers were able to read the majority of German Army Enigma messages. The Polish breakthrough had been to train professional mathematicians to help them, together with the use of a primitive processor called the ‘bomba’ or ‘bombe’ – so named because of the alarming ticking noise it made – to find the rotor settings. One of their first ‘bombes’ was a weird contraption that consisted of no fewer than six Enigma-type machines wired together to provide rapid processing of possible solutions. Polish resources were limited, and by late 1938 new advances in the Enigma machine were running ahead of the ability of the Poles to do their calculations. But the precious secrets that the Poles taught the British were enough to continue the unravelling of Enigma. The timing was an extraordinary stroke of luck, since the talented Polish cypher bureau was within two months of being broken up by the coordinated German–Soviet invasion of Poland in the autumn of 1939. Before the Polish secret service was forced to flee Warsaw, its agents had achieved the remarkable feat of stealing several examples of the military Enigma machine from the German factory where they were made.
In the late 1930s, Britain lived in the shadow of the aerial bomber. Following the tragic fate of the Spanish town of Guernica in the spring of 1937, the presumption was that the first few days of the approaching war with Germany would bring untold destruction from the air, levelling the cities of Europe. By the Munich Crisis of 1938, Whitehall had begun to make emergency preparations. Admiral Hugh Sinclair, the Chief of SIS, was busy looking for alternative wartime accommodation away from London for both SIS and GC&CS. He soon settled on a country house, Bletchley Park, near Milton Keynes in Buckinghamshire, as an ideal location for the code-breakers. Much has been made of Bletchley Park’s proximity to Oxford and Cambridge, but in fact the availability of good trunk cable communications was the dominant consideration. Bureaucratic bickering now erupted. Although GC&CS was run by the Foreign Office, its relocation was considered to be war contingency planning, so the diplomats insisted that the military pay the bill. Predictably, the War Office insisted that GC&CS was nothing to do with it, and emergency relocation for Britain’s most valuable wartime asset stalled. In the end, Hugh Sinclair bought Bletchley Park with his own money, paying over £7,500 (more than £330,000 at today’s prices). This remarkable act of generosity allowed the first wave of evacuated staff to arrive at Bletchley on 15 August 1939. Sinclair’s largesse did not stop there. He acquired a top chef from London to provide food to the code-breakers in a restaurant in the main hall, complete with full waitress service.[18]
The emphasis at Bletchley Park was distinctly military. The main body of GC&CS was initially broken up into Naval, Military and Air Sections and allocated to the ground floor of the main house, while SIS was given the top floor, indicating that it still ruled the roost. On the periphery, an ever-growing collection of numbered wooden huts – including the famous Hut Three and Hut Six – were being constructed. Particular activities were associated with each hut: typically, the core of the Enigma problem was worked on in Hut Six, while its exploitation for intelligence purposes was undertaken in Hut Three. One former code-breaker recalls that the main house was soon ‘too small for more than a handful of top brass and their immediate acolytes’. So Bletchley Park’s considerable garden, with its rosebeds and delightful maze, gradually disappeared beneath the expanding penumbra of temporary structures.[19] The shadow of the bomber even reached out to Bletchley Park. The radio transmission infrastructure involved elaborate aerials which had the potential to give away the site’s location from the air. Accordingly, Bletchley Park’s own radio station was moved to nearby Whaddon Hall. As the operation gained momentum, other nearby premises were absorbed. Elmers School, a neighbouring boys’ boarding establishment, was requisitioned for the GC&CS Diplomatic Sections.
Bletchley Park was Admiral Sir Hugh Sinclair’s last bequest to Britain’s sigint community. Through the early autumn of 1939 it was clear that he was terminally ill with cancer. His deputy and heir apparent, Stewart Menzies, was not regarded as a great brain, and indeed despised intellectuals. Sir Alexander Cadogan, the Permanent Under-Secretary at the Foreign Office, vigorously resisted the idea that Menzies might succeed Sinclair, and argued for someone from outside SIS