Created by the Atomic Energy Act of 1946, the civilian Atomic Energy Commission (AEC) oversaw US nuclear policy. Although a civilian association, it operated via military-style security protocols. Beginning in 1947, Oppenheimer served on the AEC’s General Advisory Committee. In 1954, under the leadership of its chair, Lewis Strauss, the AEC voted to revoke Oppenheimer’s security clearance.

During the winter of 1942-43, Haakon Chevalier approached Oppenheimer on behalf of George Eltenton, a young British chemical engineer who wanted to pass atomic information to the Soviet consulate in San Francisco. By this time, Oppenheimer had accepted the directorship of the bomb program but had not yet relocated to Los Alamos. The conversation between the two men, which occurred in the kitchen of Oppenheimer’s Berkeley home, became known as the “Chevalier Affair.” Oppenheimer dismissed the request, and nothing came of it, but he waited six months before reporting it to Army counterintelligence. Even then, he was reluctant to name his friend Chevalier. Gen. Groves and others believed Oppenheimer’s account, but the Chevalier Affair became a note in the physicist’s security file and came back to haunt him at his 1954 hearing.