Alastair Denniston - World War I and Interbellum

World War I and Interbellum

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.

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 26 July 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.