He had learned to cooperate for survival in the Soviet Union, where the NKVD—the KGB of its day—had knocked out all his teeth and kept him in solitary confinement for months. But in Germany as in the USSR he withheld as much information as he dared. His private endorsement of 94, to be transmuted by chain reaction from natural uranium, probably contributed to the neglect of isotope separation in Germany. After the summer of 1941 the German bomb program depended entirely on uranium and Vemork heavy water.
Fritz Houtermans
