Truman disagreed with Churchill - one of their few differences. But his reason was the same. He wanted to wait until he knew that the bomb was about to be tested. He hoped that a successful test would add to his bargaining weight more than the departure of a few American units from Europe would take away.
The first successful bomb was tested at Alamogordo on July 16. Truman had his first meeting with Joseph Stalin at Potsdam on July 17. Truman had what he wanted - the knowledge that the bomb worked. His vigor and willingness to talk back to Stalin surprised and delighted Churchill, who had been concerned that Truman would be less willing to stand firm than Franklin Delano Roosevelt would have been.
A corollary to the above is that Truman and many of his advisers thought it would be desirable to have the atom bomb tested successfully before the Soviets entered the Pacific war. Stalin had promised Roosevelt at Yalta that they would do that. By the spring of 1945, with the Germans defeated and Japanese defeat clearly visible and inevitable, with or without Soviet help, Truman and his friends began to regret the price his predecessor had been willing to pay to get the Russians into the war.
Manchuria was only part of the traditionally Chinese territory that Stalin expected to get out of entering that war.
Nowhere else was the news of the dropping of the bomb greeted with more relief than among American infantrymen in the Pacific preparing to storm beaches of Japan. To them, it meant rescue from an ordeal that they would prefer to avoid. Many would not have survived.
But was the dropping of the bomb necessary to bring about a Japanese surrender before the invasion planned for Nov. 1?
The best authority on this subject has to be Truman's chief military adviser, Admiral Leahy. The admiral, who was also chairman of the US Joint Chiefs of Staff and the Combined US and British Chiefs of Staff, wrote in his book, ''I Was There'' (1950), the following:
''It is my opinion that the use of this barbarous weapon at Hiroshima and Nagasaki was of no material assistance in our war against Japan. The Japanese were already defeated and ready to surrender because of the effective sea blockade and the successful bombing with conventional weapons.''