 Hans Bethe once said that Klaus Fuchs was the only physicist he knew who truly changed history. Because the head of the Soviet project, Lavrenti 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's fission information had a substantial effect. 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.
