Intercept!

A top-secret cryptographic dictionary compiled by Bletchley Park in 1944 defined ‘Y Service’ as ‘The organisation responsible for the interception of all enemy and neutral radio transmissions’. The job description was succinct, the task huge. The Y Service staff who intercepted and recorded the German and Japanese transmissions are unsung heroes of the attack on the enemy codes. Many of them were women. Their difficult and painstaking work was less glamorous than codebreaking, but without Y the Bletchley cryptanalysts would have had nothing to decrypt. Chapter 2 sketches the growth of the Y Service between the wars, including the establishment of the Royal Navy intercept site at Flowerdown, the Royal Air Force site at Cheadle, and the Army site at Chatham (see photograph 40). These and other military sites in the UK tended to focus on Morse transmissions. Curiously, the interception of the non-Morse transmissions associated with Fish fell at first to the London Police. Collaboration between the Foreign Office signals interception programme and Scotland Yard’s Metropolitan Police wireless service began in 1926 (‘wireless’ means ‘radio’). The Police wireless service, which started life in an attic at Scotland Yard, was originally set up to develop wireless for police vehicles; from 1926 the police operators had the additional brief of intercepting material of interest to the Foreign Office. In 1930 the Foreign Office started to finance the police Y section, which in turn became increasingly involved in the development of experimental equipment for Y work. Following successes against European traffic, the police operators received carte blanche to investigate ‘any curious type of transmission’. In the mid-1930s the section expanded and was relocated to buildings in the grounds of the Metropolitan Police Nursing Home at Denmark Hill in south London. Police operators first intercepted German non-Morse transmissions in 1932, on a link between Berlin and Moscow. These transmissions, which went on for ten months, were clearly experimental, and the police monitored them in conjunction with the Post Office’s Central Telegraph Office. It seems that the pre-war transmissions were unenciphered. Y’s first wartime encounter with non-Morse transmissions came in the latter half of 1940, when two stations broadcasting enciphered teleprinter code were intercepted.