The first atomic bombs were used in August of 1945. President Truman authorized their use to force Japan's surrender during World War II. The Manhattan Project developed two types of nuclear bombs, although history of the atomic bomb precedes 1945.

German scientists almost developed the first nuclear weapon, but the United States achieved it first. The scientists that created the weapons used in World War II worked from an extensive foundation of knowledge acquired throughout the long history leading to the atomic bomb.


1. Einstein's Letter

On October 11, 1939, President Franklin Delano Roosevelt sat down with an adviser to discuss a letter written by Albert Einstein. The letter informed President Roosevelt that recent developments in uranium chain reactions meant the Germans had figured out how to split uranium atoms. This put the Germans very close to the first atomic bomb. Roosevelt was hesitant at first, but he soon saw the wisdom of Einstein's words.

atomic bomb einstein letter Hulton Archive/Getty Images


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