GCHQ. Richard Aldrich
including those of France, the United States and Japan, since they all shed light on international affairs; but the most important were those of Russia.8
Both MI5 and SIS, together with intelligence officers from the three armed services, were obsessed with the threat from Bolshevik Russia in the interwar period. GC&CS followed suit. There were good reasons for making Moscow the pre-eminent target. Bolshevik agents were actively seeking to subvert the British Empire, and sigint produced operational intelligence that could be used to thwart these plots. Alastair Denniston enjoyed a major advantage, having recruited Ernst Fetterlein, the Tsar’s leading code-breaker, when he fled Russia after the Revolution of 1917, and in the 1920s GC&CS was successfully reading Soviet diplomatic cyphers. Several times during that decade the British government directly accused the Soviets of underhand activities in London, making use of these intercepts and referring to them openly. In 1923, for example, Lord Curzon publicly quoted Soviet messages intercepted by GC&CS stations in India. The Soviets responded by changing their cyphers, but Fetterlein simply broke them again.9
However, in May 1927, a year after the General Strike, a disastrous row erupted over secret support from Moscow for the strikers and the distribution of subversive propaganda in Britain. A veritable centre for Soviet subversion was being run under the cover of its Trade Mission, located in the Arcos building in Moorgate. The building was raided on 12 May, but advance warning allowed the Soviets to destroy most of the incriminating material. The Prime Minister, Stanley Baldwin, was embarrassed. He ardently desired to break off relations with Moscow, but having failed to garner any incriminating evidence from the Arcos raid, he turned to the priceless intercepts provided by GC&CS. To the dismay of the code-breakers, Baldwin and his Foreign Secretary, Neville Chamberlain, read out four decyphered Soviet telegrams in Parliament in order to make their case. Alastair Denniston was especially bitter about this flagrant compromise of GC&CS secrets.10
Henceforth, the Soviets changed their cyphers and deployed more secure systems for communications with diplomatic and commercial missions overseas, including their intelligence stations. They now used the ‘one-time pad’ for their more important communications. The one-time pad was a breakthrough system created by an American army officer, Major Joseph Mauborgne, during the First World War and widely adopted by other powers. It involved using a sheet of random numbers to encypher a message. Each letter in the message was given a number. Each number was then added to another from a stream of random numbers taken from a sheet on the one-time pad. The result was a sheet of text that consisted simply of groups of five numbers, one after another. Recipients could decode the message if they possessed the same sheet from the same one-time pad. If that sheet was used only once – hence the name – and for a single message, the lack of repetition prevented decryption. In short, the code was unbreakable. The disadvantage was that it was slow and cumbersome, and therefore it was reserved for high-grade secrets. Moreover, vast numbers of pads with lists of random numbers were required. No country, not even the security-obsessed Soviet Union, could send all its communications by this means.11
Nevertheless, after 1927, few Soviet diplomatic messages were being read by GC&CS. The only high-grade Soviet traffic that was decyphered were the messages of the Comintern, the part of the Soviet Communist Party that dealt with relations with Communist parties overseas. This effort was led by John 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