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J.R. Oppenheimer and General Groves

Trinity, July 16, 1945DAWN OF THE ATOMIC ERA

As the war entered its final phase, the Manhattan Project became an increasingly important and controversial element in American strategy.  Debate over how to use the bomb began in earnest in early summer of 1945.  The Trinity atomic test of July 16 (right) confirmed that the stakes for this decision were very high.  With a blast equivalent of approximately 21 kilotons of TNT, the test explosion was greater than had been predicted, and the dispersal of radioactive fallout following the test made safety something of a near thing.  News of the success at Trinity reached President Harry S. Truman at the Potsdam Conference.

Devastation at HiroshimaFollowing consultations with his advisers, Truman made the decision to use the bomb against Japan as soon as the first weapon was ready.  Little Boy, the untested uranium bomb, was dropped first at Hiroshima, Japan, on August 6, 1945, while the plutonium weapon, Fat Man, followed three days later at Nagasaki on August 9.  Use of the bomb helped bring an end to the war in the Pacific, with Japan surrendering on August 14. The most destructive war in human history was finally over.  The Manhattan Project had fulfilled its mission.

To learn more about any of these events associated with the dawn of the atomic era, choose a web page from the menu below.  To conclude your quick overview of the Manhattan Project, jump ahead to the description of its "Postscript, the Nuclear Age, 1945-present."

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Sources and notes for this page.

Portions of the text for this page were adapted from, and portions were taken directly from the Office of History and Heritage Resources, publications: F. G. Gosling, The Manhattan Project: Making the Atomic Bomb (DOE/MA-0001; Washington: History Division, Department of Energy, January 1999), 45, and Terrence R. Fehner and F. G. Gosling, Origins of the Nevada Test Site (DOE/MA-0518; Washington: History Division, Department of Energy, December 2000), 31-32.  "Atomic" and "nuclear" are basically synonymous; much as the term "pile" gradually gave way to "reactor," "atomic" was gradually replaced by "nuclear" during the later years of the Manhattan Project and afterwards.  Click here for more information about the photograph of the Trinity test.  The photograph of the lone soldier walking through an almost-completely leveled portion of Hiroshima is courtesy the Department of the Navy (via the National Archives).

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