The Soviet Union was not invited to share in the new weapons developed by the United States and the other Allies. During the war, information had been pouring in from a number of volunteer spies involved with the Manhattan Project (known in Soviet cables under the code-name of "Enormoz"), and the Soviet nuclear physicist Igor Kurchatov was carefully watching the Allied weapons development. It came as no surprise to Stalin when Truman had informed him at the Potsdam conference that he had a "powerful new weapon." Truman was shocked at Stalin's lack of interest. Stalin was nonetheless outraged by the situation, more by the Americans' guarded monopoly of the bomb than the weapon itself. Some historians share the assessment that Truman immediately authorized nuclear weapons as a "negotiating tool" in the early Cold War. In alarm at this monopoly, the Soviets urgently undertook their own atomic program.