During the conference, Truman told Stalin somewhat vaguely that America had a “powerful new weapon,” and Stalin stated that America should feel free to use it.2 What Truman did not know at the time was that the Soviet Union had a robust spy operation running in the United States, including spies within the Manhattan Project. One of the Manhattan Project physicists, Dr. Karl Fuchs, was sending bomb development data to the Soviets. Ironically, Stalin knew about the atomic bomb long before Truman did.
