The Soviet Union was not informed officially of the Manhattan Project until Stalin was briefed at the Potsdam Conference on July 24, 1945, by U.S. President Harry S. Truman, eight days after the first successful test of a nuclear weapon. Despite their wartime military alliance, the United States and Britain had not trusted the Soviets enough to keep knowledge of the Manhattan Project safe from German spies; there were also concerns that, as an ally, the Soviet Union would request and expect to receive technical details of the new weapon.