Alastair Denniston

Commander Alexander Guthrie Denniston (1 December 1881 – 1 January 1961) was a Scottish codebreaker, deputy head of the Government Code and Cypher School (GC&CS) and hockey player. Denniston was appointed operational head of GC&CS in 1919 and remained so until February 1942.

Early life Denniston was born in Greenock, Renfrewshire, the son of a medical practitioner. Room 40 was merged with its counterpart in the Army, MI1b in 1919, renamed the Government Code and Cypher School (GC&CS) in 1920 and transferred from the Navy to the Foreign Office. Denniston was chosen to run the new organisation.

With the rise of Hitler, Denniston began making preparations. Following the practice of his superiors at Room 40, he contacted scientists from Oxford and Cambridge (including Alan Turing and Gordon Welchman), asking if they would be willing to serve if war broke out. Bletchley Park was chosen by MI6 chief Admiral Hugh Sinclair as the location for the codebreaking effort because it was at a rail junction on the west coast main line north of London with good rail connections to Oxford and Cambridge. Sinclair acquired the Bletchley Park property, and Denniston was assigned to prepare the site and design the huts to be built on the grounds. The GC&CS moved to the new location in August 1939, just before the invasion of Poland and the start of the Second World War. Its name changed to Government Communications Headquarters (GCHQ).

Second World War Denniston remained in command until he was admitted to hospital in June 1940 for a bladder stone. Although ill, he flew to the United States in 1941 to make contact with American cryptographers including William Friedman. Denniston returned to Bletchley Park for a while but moved to London later in 1941 to work on diplomatic traffic. The advent of Banburismus shortly afterwards showed his pessimism to be misplaced.

In October 1941, the originator of the technique, Alan Turing, along with fellow senior cryptologists Gordon Welchman, Stuart Milner-Barry and Hugh Alexander wrote to Churchill, over the head of Denniston, to alert Churchill to the fact that a shortage of staff at Bletchley Park was preventing them from deciphering many messages. An addition of personnel, small by military standards, could make a big difference to the effectiveness of the fighting effort. The slow response to previous requests had convinced them that the strategic value of their work was not understood in the right quarters. In the letter, there was praise for the 'energy and foresight' of Commander Edward Travis.

Churchill reacted to the letter immediately, ordering "Action this day". Resources were transferred as fast as possible.

In February 1942, GC&CS was reorganised. Travis, Denniston's second in command and chief of the Naval section, succeeded Denniston at Bletchley Park, overseeing the work on military codes and ciphers. When Travis took over, he "presided over an administrative revolution which at last brought the management of Intelligence into line with its mode of production".

Denniston retired in 1945, and later taught French and Latin in Leatherhead. 2 January 1933 appointed a Commander of the Order of the British Empire (CBE) Commander Alexander Guthrie Denniston, O.B.E., R.N.V.R. Head of a Department, Foreign Office. 12 June 1941 appointed a Companion of the Order of St Michael and St George (CMG) Commander Alexander Guthrie Denniston, C.B.E., R.N.V.R. (Retd.), Head of a Department of the Foreign Office.

Appointed Officer 7 January 1918

Fictional depictions

In the 2014 film The Imitation Game, he is portrayed by Charles Dance.