Kurchatov’s memoranda confirm Fuchs’s importance as a spy. They also reveal that the Soviet Union had other sources of information in the Manhattan project. Anatolii Iatskov, who – under the name of Anatolii Iakovlev – was Harry Gold’s NKGB case officer in New York, has said that at most one half of his network of agents was uncovered by the FBI.84 It is clear, for example, that someone was passing on information about the work of Seaborg and Segrè at Berkeley. But the available evidence suggests that Fuchs was by far the most important informant in the Manhattan project.85
