On August 6, 1945, the U.S. dropped an atomic bomb on Hiroshima, Japan. Since 1940, the United States had been working on an atomic weapon after learning that Nazi Germany was working on nuclear weapons. By the time the U.S. conducted its first successful test, Germany had been defeated. The war against Japan in the Pacific, however, continued. President Harry S. Truman ordered that the new weapon be used to bring the war to a speedy end.
