I went with Truman to Potsdam, outside conquered Berlin, in late July 1945, to a conference of the Allies to discuss the shape of the postwar world. We had not yet dropped the atom bomb on Japan, but we were about to, as soon as the weather was favorable. Secretary of War Henry Stimson gave us a statement to be released to the press as soon as the bomb was dropped. We were sitting in our temporary Map Room in a villa in a Berlin suburb when the message [for the day of the eventual bombing] arrived. Truman signed it-but didn't want to be questioned by Stalin. He didn't want to be cross-examined about how the bomb worked or why we used it. We had given the Russians a hint. Truman had said we have a powerful new weapon, and Stalin simply said, "I hope you put it to good use." Truman came back and said he didn't think Stalin had any idea what he was talking about. We were very much concerned about secrecy. We hadn't worked out yet any sort of postwar plans with the control of atomic energy in any form. It was just premature to spread the word around. We had no thought of a cold war-yet. We didn't know then that Soviet spies had already stolen the secret of the bomb.