The Decision to Drop
the Atomic Bomb

U.S. officials became interested in nuclear weapons in the late 1930s when scientists fleeing Nazi Germany alerted President Roosevelt to German experiments in nuclear fission. The Manhattan Project—the code name given to the U.S. atomic program—was formally set up in 1942 under the direction of General Leslie Groves and physicist J. Robert Oppenheimer. The program was a massive undertaking, employing thousands of workers at sites in Chicago; Berkeley, California; Oak Ridge, Tennessee; Hanford, Washington; and, most famously, at the scientific laboratory in Los Alamos, New Mexico. It took $3 billion to create the atomic bombs. The project was so secretive that even Harry Truman didn’t learn of it until he became president following Roosevelt’s death.

The bombs that exploded over Hiroshima and Nagasaki in August 1945 revolutionized world history. They ended World War II, changed the nature of warfare, and altered the course of international relations. The bombs launched a nuclear arms race that continued throughout the Cold War and unleashed fears of global annihilation. The United States is the only country to use nuclear weapons against an enemy, and debates about whether the bombs were necessary began even before they were dropped. Scientists, officials in the Truman administration, military figures, and ordinary citizens all grappled with the meaning and consequences of this nuclear action. As a result of the bombing of Hiroshima and Nagasaki, more than 200,000 people, mostly civilians, were killed immediately, and even more were stricken with radiation poisoning, burns, and other injuries. More than 80 percent of the buildings in each city were flattened instantly, and permanent shadows were left on walls and pavement.

Many aspects of Truman’s decision continue to be questioned and debated. Were the bombs the only way to end the war with Japan? Should the alternatives of blockading or using conventional bombs have been tried? Should the United States have given Japan an explicit warning about the bomb or demonstrated its effectiveness on an uninhabited island? Did racist attitudes about the Japanese influence the decision? Was the motive revenge or saving American lives? The following documents help explore these and other questions about America’s use of atomic weapons in World War II.