Emil Julius Klaus Fuchs (b. December 29, 1911, Rüsselsheim, Germany – d. January 28, 1988, East Berlin, East Germany) was a German physicist who was convicted of surreptitiously supplying information on the British and American atomic bomb research to the USSR.

Fuchs joined the Communist Party of Germany, but fled to England following the rise of the Nazis in 1933. Gaining a doctorate in Physics from the University of Bristol in 1937, he was invited to study at Edinburgh University.

At the outbreak of war, German citizens were interned, Fuchs at a camp in Quebec, Canada. However Professor Max Born of Edinburgh University intervened on Fuchs' behalf. By early 1941, Fuchs had returned to Edinburgh where he was approached by Rudolf Peierls to work on the "Tube Alloys" program, the British atomic bomb research project. He became a British citizen in 1942.

In late 1943 Fuchs transferred to Columbia University, New York City to work on the Manhattan Project. From August 1944 Fuchs worked in the Theoretical Physics Division at Los Alamos, New Mexico under Hans Bethe. His chief area of expertise was the problem of imploding the fissionable core of the bomb. He was present at the Trinity test.

Fuchs passed detailed information on the project to the Russians through Harry Gold in 1945 and further information about the hydrogen bomb in 1947. But it was not until 1948 that it was discovered that the Manhattan Project security had been breached and not until 1949, when Fuchs had returned to England and the Harwell Atomic Energy Research Establishment, that he was confronted by intelligence officers as a result of the cracking of Soviet ciphers known as the VENONA project. Under interrogation by Jim Skardon, Fuchs was prosecuted by Sir Hartley Shawcross. Fuchs confessed in January 1950 and was convicted on March 1, 1950 and sentenced the next day to fourteen years in prison, the maximum possible for passing military secrets to a friendly nation. A week after the verdict, on March 7, the Soviet Union issued a terse statement denying that Fuchs served as a Soviet spy.

Fuchs' testimony to British and American intelligence agencies eventually led to the trials of David Greenglass and Julius and Ethel Rosenberg in the USA.

It is not known how much Fuchs aided either the Soviet atomic or hydrogen bomb projects directly, except perhaps of evidence of American interest in nuclear weapons. Because of the manner in which the head of the Soviet project, Lavrentii Beria, used foreign intelligence (as a third-party check, rather than giving it directly to the scientists, as he did not trust the information by default) it is unknown whether Fuchs' fission information had a substantial impact (and considering that the pace of the Soviet program was set primarily by the amount of uranium they could procure, it is hard for scholars to accurately judge how much "time" this saved the Soviets). The information Fuchs passed on the hydrogen bomb was too early to be of much material use: the key methods of making a hydrogen bomb work had not yet been discovered in the United States during the time Fuchs was working on the project.

On June 23, 1959 Fuchs was released and allowed to emigrate to Dresden, East Germany where he resumed a scientific career.

External link

• http://www.spartacus.schoolnet.co.uk/USAfuchs.htm
• Klaus Fuchs' 1950 confession
• PBS.org on Fuchs, with photo
• German Goncharov on: What the Soviets Learned From Klaus Fuchs
• Communist spy jailed for 14 years (BBC News)