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The Manhattan Project -- Its Immediate Influences

by Mary Schorn on Mon, December 17, 2012

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The Manhattan Project -- Its Immediate Influences

With the Manhattan Project on the brink of success in spring 1945, the atomic bomb became an increasingly important element in American strategy to bring an end to World War II.

Because of the generally accepted view that the Japanese would fight to the bitter end, a costly invasion of the home islands seemed likely, even 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.  They contended that the bomb could possibly lead to Japanese surrender without an invasion and should be used as soon as possible, without warning.

Strategies for forcing Japanese capitulation occupied center stage in June 1945.  Wording of an early surrender offer received considerable attention, the sticking point being the term “unconditional.” It was clear that the Japanese would fight on rather than accept terms that would eliminate the Imperial House or demean the warrior tradition, but American policy makers feared that anything less than a more democratic political system and total demilitarization might lead to Japanese aggression in the future. The definition of unconditional surrender was clarified.  Japan need not fear total annihilation.  Once demilitarized, Japan would be free to choose its political system and would be allowed to develop a vibrant economy.  It was hoped that this public statement to Japan would lead to surrender before a costly invasion would have to be launched.  However, the Japanese continued to search for an alternative to unconditional surrender.

On July 26, 1945, a formal warning was given to Japan.  The message called for the Japanese to surrender unconditionally or face “prompt and utter destruction.”  The Potsdam Proclamation left the emperor’s status unclear by making no reference to the royal house in the section that promised the Japanese that they could design their new government as long as it was peaceful and more democratic.

Japanese wanted to surrender but felt they could not accept the terms offered in the Potsdam Proclamation. American policy makers, however, anxious to end the war without committing American servicemen to an invasion of the Japanese homeland, were not inclined to undertake revisions of the unconditional surrender formula and cause further delay.  A blockade of Japan combined with conventional bombing was rejected as too time-consuming and an invasion of the islands as too costly. And few believed that a demonstration of the atomic bomb would convince the Japanese to give up. Primarily upon these grounds, American policy makers concluded that the atomic bomb must be used.  Information that Hiroshima might be the only prime target city without American prisoners in the vicinity placed it first on the list.

In the end, in the early morning hours of August 6, 1945, the Enola Gay released the untested 9,700-pound uranium bomb, nicknamed Little Boy, above Hiroshima, an important military and communications center.  Little Boy detonated 1900 feet above the city and caused total devastation for five square miles.  Japan was then warned that if it still refused to surrender unconditionally as demanded by the Potsdam Proclamation of July 26, the United States would attack additional targets with equally devastating results.

In the absence of a surrender announcement, on August 9, a second atomic attack took place. The bomber, Bock's Car, approached Nagasaki, home to the Mitsubishi plant that had manufactured the torpedoes used at Pearl Harbor, and dropped her single payload, a plutonium bomb weighing 10,000 pounds and nicknamed Fat Man.  Three square miles of the city were destroyed.

Still the Japanese leadership struggled to come to a decision. Word finally reached Washington early on August 10 that the Japanese, in accordance with the emperor’s wishes, would accept the surrender terms, provided the emperor retain his position. A third atomic attack was held up while the United States considered a response, finally taking a middle course and acknowledging the emperor by stating that his authority after the surrender would be exercised under the authority of the Supreme Commander of the Allied Powers.

Japan surrendered on August 14, 1945 and the Instrument of Surrender was signed on September 2, 1945.  This ended the war that began for the United States with the surprise attack at Pearl Harbor on December 7, 1941.

- Edited excerpts from The Manhattan Project:  Making the Atomic Bomb

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