On February 2, 1950, Dr. Klaus E. J. Fuchs, Chief of the Theoretical Physics Division of the British Atomic Energy Research Establishment at Harwell, was arrested in London and charged with engaging in espionage for the Soviet Union. A German-born naturalized British citizen, Fuchs was one of about 20 British scientists who came to the United States in December 1943 to contribute to the development of the atomic bomb. From December 1944 to June 1946 Fuchs worked at Los Alamos Laboratories where he was intimately involved in the development of the atomic bomb and may have had access to information relevant to hydrogen bomb development. In 1946 he returned to England to participate in the British atomic energy program. In November 1947 he once more visited the United States, representing the United Kingdom in a tripartite atomic energy information declassification conference in Washington. He visited certain atomic energy installations during his stay in the United States.
On February 10, 1950, Dr. Fuchs admitted in a signed statement that he had transmitted atomic energy information to the Soviet Union during and after the Second World War because he had been devoted to Communism. On March 1 Fuchs pleaded guilty and received the maximum 14 years’ sentence under the British Official Secrets Act.