The Manhattan Project: Making the Atomic Bomb

With the Manhattan Project on the brink of success in spring 1945, the atomic bomb became an increasingly important element in American strategy. A long hoped-for weapon now seemed within reach at a time when hard decisions were being made, not only on ending the war in the Pacific, but also on the shape of the postwar international order.

From Roosevelt to Truman

On April 12, only weeks before Germany's unconditional surrender on May 7, President Roosevelt died suddenly in Warm Springs, Georgia, bringing Vice President Harry S. Truman, a veteran of the United States Senate, to the presidency. Truman was not privy to many of the secret war efforts Roosevelt had undertaken and had to be briefed extensively in his first weeks in office. One of these briefings, provided by Secretary of War Stimson on April 25, concerned S-1 (the Manhattan Project). Stimson, with 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 were attacking Japanese cities at will. A single fire bomb 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.

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