Explore the top-secret American project to build the world's first atomic bomb.

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

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.

President Harry Truman orders the Enola Gay to drop the atom bomb on Hiroshima, Cy Young joined major league baseball, the first woman swims the English Channel, and Jamaican independence is declared in This Day in History video. The date is August 6th. The atom bomb was also dropped on Nagasaki which helped end World War II when Japan surrendered.

On October 12, 1949, two weeks after President Harry Truman announced that Russia had developed the atom bomb, Gen. Omar Bradley, chairman of the Joint Chiefs of Staff, delivers a speech about the impact of this discovery on American policy.

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

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.