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Commander Alexander Guthrie (Alastair) Denniston CMG CBE RNVR (1 December 1881, Greenock – 1 January 1961, Milford on Sea) was a British codebreaker in Room 40 and first head of the Government Code and Cypher School (GC&CS) and field hockey player. Denniston was appointed operational head of GC&CS in 1919 and remained so until February 1942.[1]

Early lifeEdit

Denniston was born in Greenock, the son of a medical practitioner[1]. He studied at the University of Bonn and the University of Paris[1]. Denniston was a member of the Scottish Olympic Hockey team in 1908 and won a bronze medal.

World War I and interbellumEdit

In 1914 he helped form Room 40 in the Admiralty, an organisation responsible for intercepting and decrypting enemy messages. In 1917 he married a fellow Room 40 worker, Dorothy Mary Gilliat[1].

After World War I, Room 40 was merged with its counterpart in the Army, MI1b, to become the Government Code and Cypher School in 1919. Denniston was chosen to run the new organisation.

On July 26, 1939, just five weeks before the outbreak of World War II, Denniston was one of three Britons (along with Dilly Knox and Humphrey Sandwith) who participated in the trilateral Polish-French-British conference held in the Kabaty Woods south of Warsaw, at which the Polish Cipher Bureau initiated the French and British into the decryption of German military Enigma ciphers[2].

World War IIEdit

With the outbreak of World War II in 1939, GC&CS greatly expanded and relocated to Bletchley Park.

In February 1942, GC&CS was reorganised, and Denniston was placed in charge of a civil and diplomatic division in London, while Edward Travis succeeded him at Bletchley Park, overseeing the work on military codes and ciphers.

Post-war lifeEdit

Denniston retired in 1945, and later taught French and Latin in Leatherhead[1].

Honours and awardsEdit


  1. 1.0 1.1 1.2 1.3 1.4 1.5 F. H. Hinsley, revised by Ralph Erskine, "Denniston, Alexander Guthrie [Alastair] (1881-1961), cryptanalyst and intelligence officer", Oxford Dictionary of National Biography, 2004
  2. Ralph Erskine, "The Poles Reveal their Secrets: Alastair Denniston's Account of the July 1939 Meeting at Pyry", pp. 294-305, Cryptologia 30(4), 2006
  3. Template:LondonGazette
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  5. Template:LondonGazette

External linksEdit

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