John Cairncross

United Kingdom state institutions Marxism–Leninism 1913–1995 ○ Died of a stroke

The alleged fifth man of the Cambridge Five, who passed Bletchley Park decrypts of German traffic to the Soviets

Born in Lanarkshire, Scotland, he studied at Glasgow, the Sorbonne and Trinity College, Cambridge, and joined the Communist Party of Great Britain. Placed first in the Foreign Office examination of 1936, he worked in the Foreign Office, the Treasury and the Cabinet Office while passing information to Soviet intelligence. In 1942 and 1943, working in Hut 3 of the Government Code and Cypher School at Bletchley Park, he smuggled out Tunny decrypts due to be destroyed and handed them to his NKVD contact in London; the material may have influenced the Battle of Kursk. He confessed in secret to MI5 in 1964 but was never prosecuted, and his identity as the fifth man of the Cambridge Five was confirmed only in 1990.