The K-25 plant in Oak Ridge, Tennessee, was built to enrich uranium for the atomic bomb.

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Watch actual footage of the first atomic bomb being prepared by U.S. engineers in 1945.

Former banker and hydrogen bomb champion Lewis Strauss addresses the U.N. on nuclear energy. Strauss was appointed to the U.S. Atomic Energy Commission (AEC) in 1946 and served as its chairman from 1953 to 1958. In September 1956 U.N. delegates gathered to approve a new international atomic energy agency.

On July 3, 1987, 42 years after dropping the atomic bomb on Hiroshima, Enola Gay pilot Paul Tibbets recalls his mindset during the fateful mission on August 6, 1945.

In his radio address to the American people, on August 9, 1945, President Harry Truman speaks about the Hiroshima bombing, and reasserts his threat to use additional atomic bombs against Japan until it surrenders.

Shots of a test nuclear explosion in Hawaii. | Courtesy of the Department of Energy Nevada Operations Office