John Cairncross (1913-1995) was a Scottish civil servant who spied for the Soviet Union and is often called the “fifth man” of the Cambridge spy ring. Recruited in the 1930s, partly through Anthony Blunt’s talent spotting, he entered the Foreign Office in 1936. In 1940 he became private secretary to Lord Hankey, a cabinet minister with access to scientific and intelligence matters, and passed Soviet intelligence early material on the British atomic bomb project.

From 1942 to 1943 he worked at Bletchley Park, where he supplied the Soviets with decrypted German communications, including intelligence relevant to the July 1943 Battle of Kursk. He then served in MI6. Suspicion fell on him in 1951 after papers in his handwriting were found in Guy Burgess’s flat; he resigned from government service and moved abroad. He made an admission to MI5 in 1964 and was not prosecuted. Oleg Gordievsky’s information led to his public identification as the fifth man in 1990. Cairncross died in 1995; his memoir, The Enigma Spy, appeared in 1997.

Sources

• Cairncross, John. The Enigma Spy: An Insider’s Story. Century, 1997.
• Andrew, Christopher, and Oleg Gordievsky. KGB: The Inside Story of Its Foreign Operations from Lenin to Gorbachev. HarperCollins, 1990.
• Andrew, Christopher. Defend the Realm: The Authorized History of MI5. Alfred A. Knopf, 2009.

Summary entry. A fuller, document-based profile is in preparation.