GCHQ. Richard Aldrich
his Radio Operators a seasonal greeting using the same obvious formula in no fewer than six different codes. Up until that point the British had only been able to read one of these codes, but with these clues they could read all six. In the First World War, the Second World War and again in the Cold War, poor discipline by the human operators often proved to be the great weakness in otherwise impregnable cypher systems.[4]
The Royal Navy code-breakers, who had established themselves in the Admiralty’s ‘Room 40’, achieved even greater success. Famously, they broke the ‘Zimmermann Telegram’, a message sent from the German Foreign Minister, Arthur Zimmermann, suggesting an alliance between Germany and Mexico against the United States. As an inducement, Mexico was to be offered the return of her lost territories in Texas, New Mexico and Arizona. These revelations, made public in March 1917, were central in bringing the United States into the First World War on the side of Britain and France. The American entry into the war, together with a tightening blockade, persuaded Germany to seek an armistice the following year. The code-breakers of Room 40 celebrated with champagne. There are few more significant examples of the direct impact of code-breaking upon international relations.[5]
In 1919 the British government’s Secret Service Committee, chaired by Lord Curzon, the rather formidable Foreign Secretary, recommended that a unified peacetime code-breaking agency should be created. This involved the difficult merger of two quite separate organisations. The head of the Army code-breakers, Major Malcolm Hay, was awkward and argumentative, while his naval equivalent, Commander Alastair Denniston, proved to be suave and diplomatic. Denniston secured the job as chief of a new combined code-breaking organisation, which initially consisted of around two dozen intelligence officers and a similar number of clerical staff, and found himself installed in splendid accommodation at Watergate House in The Strand, next to the Savoy Hotel. Formed on 1 November 1919, the new organisation was given the name ‘Government Code and Cypher School’, or GC&CS, which was not inappropriate, since the leading code-breakers devoted a great deal of time to the patient training of new initiates.[6] Both during the First World War and in the interwar period about half the staff of GC&CS and its predecessors were women, mostly in the clerical grades.
Almost immediately, GC&CS adopted a disingenuous description of its duties that would remain in place until the 1980s. Publicly, its functions were described as merely defensive; in other words, it was to assist in the provision and protection of codes and cyphers used by government departments. However, its more secret duty was to give priority to offensive activity, namely attacking the cypher communications used by foreign powers. GC&CS gradually shifted its focus to diplomatic traffic, and at the suggestion of Lord Curzon it was transferred to the control of the Foreign Office. It seemed natural that within the Foreign Office structure it should be placed under the supervision of Britain’s traditional overseas intelligence service, SIS, which recruited human spies. But a subliminal naval influence remained. The talented Chief of SIS, Mansfield Cumming (known within the organisation as ‘C’, the name by which the head of SIS would continue to be called), was a former naval officer. Cumming died in harness in 1923 and was succeeded by another sailor, the former head of Naval Intelligence, Hugh ‘Quex’ Sinclair. Naval intelligence and naval signals officers continued to exercise a profound influence on GC&CS and its successors as late as the 1970s.
The means by which Britain collected its intelligence was changing. During the First World War, much of its intelligence work had involved overhearing military wireless messages by means of receiving stations scattered around Europe, the Mediterranean and the Middle East. The shift to diplomatic traffic meant undertaking more work on encyphered diplomatic telegrams sent by cable. Each country had teams of code clerks who carefully encyphered diplomatic messages before they were sent by telegram using a worldwide network of cables. Although government cable censorship had officially ended in 1918, a private arrangement meant that all the commercial cable companies secretly handed over their traffic to GC&CS for copying. Most of the foreign embassies in London used cable companies to send their encyphered messages, and British dominance of international telecommunications networks meant that many of the world’s messages travelled over British cables at some point. Private companies such as Standard Cable & Wireless Ltd were almost an integral part of the worldwide British sigint system. This secret state–private network remained hidden until it was exposed by the journalist Chapman Pincher in February 1967 in the Daily Express under the headline ‘Cable Vetting Sensation’.[7]
In 1925 both SIS and GC&CS were moved into Sinclair’s new secret service headquarters at Broadway Buildings, opposite St James’s Park tube station, which its occupants thought ‘more dingy than sinister’. The walls of the corridors were painted dark brown to a height of about four feet from the floor, and the ancient lifts moved between the many storeys with a slow clatter. The code-breakers were given the third floor. From here, the sigint product, which consisted of the verbatim text (or sometimes summaries) of the messages of foreign governments was distributed around Whitehall in files with special blue jackets that became known as ‘BJs’. GC&CS worked on the cyphers of many countries in the interwar period, 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