Greenberg, Joel Alastair Denniston

Code-breaking From Room 40 to Berkeley Street and the Birth of GCHQ

Some of the people who contributed significantly to Bletchley Park's success in decrypting the secret messages of Britain's enemies during the Second World War have become well-known figures. However, the man who founded the organisation based there and led it from its inception in 1919 until 1942 has been surprisingly overlooked until now. In 1914, Alastair Denniston, who had previously taught French and German at Osborne Royal Navy College, was one of the first recruits to the Admiralty's newly formed code-breaking department, known as Room 40. There, a team of representatives from various professions successfully decrypted intercepted German messages during the First World War. After the armistice, Room 40 was merged with the corresponding department of the British Army MI.1 to form the Government Code and Cypher School (GC&CS). The GC&CS was initially based in London, but from August 1939 onwards, it was largely relocated to Bletchley Park, where Alastair Denniston served as director of operations. In 1942, Denniston was transferred from the military to the civilian intelligence service in Berkeley Street, London. Initially small, the decryption of diplomatic and commercial messages became increasingly important with the decline of Enigma traffic towards the end of the Second World War and became an important part of British signals intelligence. In June 1946, the GC&CS was renamed Government Communications Headquarters (GCHQ) and moved to the suburbs of Cheltenham. It remains the UK's signals intelligence organisation. With the support and assistance of the Denniston family and GCHQ, Joel Greenberg has written this story about Commander Alexander Alastair Guthrie Denniston, a man whose death in 1961 was ignored by the major newspapers and the British intelligence service that was his legacy.