Klaus Fuchs was a German-born British physicist who passed United States atomic secrets to the Soviets during World War II and was convicted of espionage in 1950. Fuchs, a communist, was forced from his native Germany by the Nazis, ending up in Britain in 1933. There he earned doctorates in physics from Bristol and Edinburgh Universities as specialist in quantum mechanics. Fuchs was teaching at Edinburgh when World War II started, but because he was a German citizen he was detained by the British government and sent to an internment camp in Canada in 1940. After six months he was allowed back to the U.K., where he was invited to join their secret research in atomic weapons. A naturalized citizen of the U.K. by 1942, Fuchs was sent to the United States, where he worked in Los Alamos on the Manhattan Project, in a significant role in the development of the atomic bomb. He returned to England after the war and worked at Harwell as a theoretical physicist, but his name popped up in the secret intelligence files known as the Venona documents, files that tracked espionage efforts by the Soviet Union. Fuchs confessed in January of 1950 of passing classified documents to the Soviets, going back to 1941. A committed communist, he saw no reason why the Russians, allies with the United States and England during World War II, should be kept ignorant of advances in atomic weaponry. After a 90-minute trial in March, Fuchs was convicted of espionage and sentenced to 14 years in prison, the maximum penalty for passing secrets to a friendly nation. He spent 9 years in jail and returned to East Germany upon his release, where he had a long career as a nuclear scientist and member of the communist Central Committee. His confession helped lead British and American authorities to Julius and Ethel Rosenberg, who were executed in 1953 for being Soviet spies.
Klaus Fuchs’s Soviet code name was “REST.”