Potsdam

News of the successful Alamogordo test reached Truman when he was at the Potsdam Conference in Germany with Britain’s Winston Churchill and the Soviet Union’s Joseph Stalin. Some of the Manhattan Project scientists suggested that the atomic bomb could end the war without an invasion of Japan. General Arnold did not think the new weapon was necessary if the blockade and incendiary bombing continued. As the AAF commander put it, “Atomic bomb or no atomic bomb, the Japanese were already on the verge of collapse.” Nonetheless, Truman came to believe that he had a choice between the invasion and use of the atomic bomb. 

Churchill contributed to this view. After learning of the successful American test, Churchill speculated that the new weapon, so different from any that had ever been developed, might give the Japanese a face-saving excuse to surrender. Thus, the British and the Americans might not need the promised Soviet entry into the war, which would expand Stalin’s influence in the Far East. President Truman informed the Soviet dictator about the new bomb without giving him any details. 

At the same time that Truman and Churchill were considering the implications of the new weapon, Stalin was preparing to declare war on Japan and invade Manchuria. The three leaders called on Japan to surrender unconditionally or face “utter devastation.” While still at Potsdam, Truman approved an order to the Joint Chiefs of Staff authorizing an atomic raid on a Japanese city sometime after August 3, 1945. By then Japan would have had time to respond to the Potsdam decisions. The Japanese government continued to resist unconditional surrender as a matter of honor. Perhaps fearing a military coup if he agreed to surrender, and hoping for a negotiated settlement, Premier Suzuki replied ambiguously to the Potsdam ultimatum. Truman interpreted Suzuki’s answer as a rejection.