Klaus Fuchs (Emil Julius Klaus Fuchs, 1911-1988) was a German-born theoretical physicist who passed atomic bomb secrets to the Soviet Union. A Communist who fled Nazi Germany in 1933, he settled in Britain, became a British subject, and joined the British atomic program. He began supplying information to Soviet military intelligence in 1941 and later to the NKGB. As a member of the British mission to the Manhattan Project, at Los Alamos from 1944 to 1946, he passed detailed information on the plutonium implosion design through his courier Harry Gold.

After returning to Britain to head theoretical physics at the Harwell atomic research establishment, Fuchs was identified through decrypted Soviet cables (the Venona project). Questioned by MI5, he confessed in January 1950 and on March 1, 1950 was convicted at the Old Bailey and sentenced to 14 years, the maximum for passing secrets to an ally. His confession led the FBI to Gold and onward to David Greenglass and Julius and Ethel Rosenberg. Released in 1959, he moved to East Germany, where he worked as a nuclear scientist until his death.

Sources

• Close, Frank. Trinity: The Treachery and Pursuit of the Most Dangerous Spy in History. Allen Lane, 2019.
• Haynes, John Earl, and Harvey Klehr. Venona: Decoding Soviet Espionage in America. Yale University Press, 1999.
• Andrew, Christopher. Defend the Realm: The Authorized History of MI5. Alfred A. Knopf, 2009.

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