ALASTAIR DENNISTON: Code-breaking From Room 40

Much more than a biography of Alexander (Alastair) Guthrie Dennison (AGD) 1881-1961, wheelhorse of the British Signal Intelligence (SIGINT) and his effort at the start of Hitler's War, it is the story of SIGINT itself starting with the World War One story of Room 40 under 'Blinker' Hall, the Director of Naval Intelligence, with a fascinating focus on the Zimmerman Telegrams so as to bring America into the war. Dennison had been teaching French and German at Osborne Royal Naval College and was one of the first recruits into the Admiralty's fledgeling code breaking section with a team drawn from a wide range of professions who successfully decrypted intercepted German communications. After the Armistice, Room 40 was merged with the British Army's equivalent section - M11 (b) to form the Government Code and Cypher School (GC&CS). Initially based in London, from August 1939 GC&CS was largely located at Bletchley Park, with Alastair Denniston at its Head. He reported to Admiral 'Quex' Sinclair, Hall's successor at DNI. The focus was on diplomatic traffic. The Office co-located in London with Quex's other baby, the Secret Intelligence Service aka MI6. Denniston was removed from his post at the beginning of 1942 and given responsibility for civil codebreaking which became of increasing importance and a vital part of Britain's signals intelligence effort. GC&CS was renamed the Government Communications Headquarters GCHQ in June 1946 and moved to the outskirts of Cheltenham where it continues to be the UK's signals intelligence gathering organisation. Denniston and this operation continued to deliver applauded results which were reported as a model for similar US activity, but he was forced into retirement in December 1944 with no knighthood. This is a superb biography of the man who created and led the organisation from its inception in 1919 until 1942 who has been surprisingly overlooked until now. It also re-writes the bad reputation he was given in the film 'The Imitation Game'. Includes photographs from the family album, 308pp in large softback. For all interested in naval, military and air force SIGINT in the UK, particularly December 1940.