Klaus Fuchs - Value of Fuchs' Data To The Soviet Project

Value of Fuchs' Data To The Soviet Project

Hans Bethe once said that Klaus Fuchs was the only physicist he knew who truly changed history. Because of the manner in which 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 (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). Some former Soviet scientists said they were actually hampered by Fuchs's data, because Beria insisted that their first bomb ("Joe 1") should resemble the American plutonium bomb ("Fat Man") as much as possible, even though the scientists had discovered a number of improvements and different designs for a more efficient weapon.

Whether the information Fuchs passed relating to the hydrogen bomb would have been useful is still somewhat in debate. Most scholars have agreed with the assessment made by Hans Bethe in 1952, which concluded that by the time Fuchs left the thermonuclear program—the summer of 1946—there was too little known about the mechanism of the hydrogen bomb for his information to be of any necessary use to the Soviet Union (the successful Teller-Ulam design was not discovered until 1951). Soviet physicists later noted that they could see as well as the Americans eventually did that the early designs by Fuchs and Edward Teller were useless. However, later archival work by the Soviet physicist German Goncharov has suggested that while Fuchs' early work (most of which is still classified in the United States, but copies of which were available to the Soviets) did not aid the Soviets in their effort towards the hydrogen bomb, it was actually far closer to the final correct solution than was recognized at the time, and indeed spurred Soviet research into useful problems which eventually resulted in the correct answer. Since most of Fuchs' work on the bomb, including a 1946 patent on a particular model for the weapon, are still classified in the United States, it has been difficult for scholars to fully assess these conclusions. In any case, it seems clear that Fuchs could not have just given the Soviets the "secret" to the hydrogen bomb, since he did not himself actually know it.