Manhattan Project: The War Enters Its Final Phase, 1945

THE WAR ENTERS ITS FINAL PHASE
(1945)
Events > Dawn of the Atomic Era, 1945

On April 12, 1945, only weeks before Germany's unconditional surrender on May 7, President Franklin Roosevelt died suddenly in Warm Springs, Georgia. Vice President Harry S. Truman, a veteran of the United States Senate, was now president. Truman had not been privy to many of Roosevelt's internal policy deliberations and had to be briefed extensively in his first weeks in office. One of these briefings, provided by Secretary of War Henry Stimson on April 25, concerned S-1 (the Manhattan Project). Stimson, with Leslie Groves present during part of the meeting, traced the history of the Manhattan Project, summarized its status, and detailed the timetable for testing and combat delivery. Truman asked numerous questions during the forty-five minute meeting and made it clear that he understood the relevance of the atomic bomb to upcoming diplomatic and military initiatives.

By the time Truman took office, Japan was near defeat. American aircraft, especially B-29s (right), were bombing Japanese cities at will. A single firebomb raid in March killed nearly 100,000 people and injured over a million in Tokyo. A second air attack on Tokyo in May killed 83,000. Meanwhile, the United States Navy had cut the islands' supply lines. But because of the generally accepted view that the Japanese would fight to the bitter end, a costly invasion of the home islands seemed likely, though some American policy makers held that successful combat delivery of one or more atomic bombs might convince the Japanese that further resistance was futile.

Strategies for forcing Japan's surrender assumed center stage. At the February 1945 Yalta Conference (left), the Soviet Union agreed to enter the war against Japan once Germany was defeated. The Allies had long called for the unconditional surrender of Germany and Japan, but Joseph C. Grew, the Acting Secretary of State, urged that it be made publicly clear that this did not mean Japan's total annihilation. Once demilitarized, Japan would be free to choose its political system and would be allowed to develop a vibrant economy. Grew hoped that a public statement to Japan would lead to surrender before a costly invasion would have to be launched. The Joint Chiefs of Staff remained doubtful that this was possible, however, and continued to advocate a ground invasion of Japan itself, a plan identified as Operation Olympic. Stimson hoped that an invasion could be avoided, either by redefining the surrender terms or by using the atomic bomb.

Preparations continued for the physical delivery of atomic bombs to their targets. In September 1944, at Wendover Field in western Utah, Colonel Paul Tibbets (right) had begun drilling the hand-picked bomber crews that comprised the 393rd Bombardment Squadron of the 509th Composite Wing, Army Air Force. Though the precise nature of their mission was kept secret from all but Tibbets, the pilots and crews knew something strange was afoot, as they repeatedly practiced dropping single, huge (5,500-pound) dummy bombs from their new B-29 long-range bombers. (They nicknamed these orange bombs "pumpkins.") After the surrender of Germany to the Allies in May, it was clear that the bomb would be used on the only remaining combatant: Japan. The following month, Tibbets moved his command to Tinian Island in the Marianas Islands of the western Pacific, where the Navy Seabees had built the world's largest airport to accommodate the large B-29s that were already bombing Japan's cities. Preparations for the use of the bomb were nearing completion, but the question of how to use it remained.

Sources and notes for this page.

The text for this page was adapted from, and portions were taken directly from the Office of History and Heritage Resources publication: F. G. Gosling, The Manhattan Project: Making the Atomic Bomb (DOE/MA-0001; Washington: History Division, Department of Energy, January 1999), 42, 45-46. The photographs of "D-Day," the B-29s, and the Yalta Conference are courtesy the National Archives. The photograph of Harry Truman taking the oath of office is courtesy the Truman Presidential Museum and Library. The photograph of Paul Tibbets with his ground crew in front of the Enola Gay is reproduced from Vincent C. Jones, Manhattan: The Army and the Atomic Bomb, United States Army in World War II (Washington: Center of Military History, United States Army, 1988), 535.

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