Fuchs was a German-born theoretical physicist who worked in Los Alamos on the atom bomb project. He was responsible for many significant theoretical calculations relating to the first fission weapons and early models of the hydrogen bomb.
Whilst attending university in Germany, Fuchs became involved with the Communist Party of Germany.
After a run-in with the newly installed Nazi government, he fled to England where he earned his PhD in physics. For a short time he worked on the British atomic bomb project.
It was while he was working for the British that he began to give information to the Soviets. He reasoned that they had the right to know what the British and the Americans were developing.
In 1943 he was transferred to the United States to assist on the Manhattan project. From 1944 he worked in New Mexico at Los Alamos.
For two years he gave his KGB contacts theoretical plans for building a hydrogen bomb. He also provided key data on the production of uranium 235, allowing the Soviets to determine the number of bombs possessed by the United States.
On his return to the United Kingdom in 1946, he was interrogated as a result of the cracking of some Soviet ciphers. He was tried and sentenced to fourteen years in prison, the maximum term under British law for passing military secrets to a friendly nation.
He was released after nine years and immediately moved to Germany where he lived out the remainder of his life.
