The Decision to Drop the Atomic Bomb

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. Debates about whether the bombs were necessary began even before they were dropped (Documents 23.5 and 23.6). 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 (Documents 23.7 and 23.9).

Many aspects of Truman’s decision continue to be questioned and debated, especially whether there were reasonable alternatives to dropping the two atomic bombs (Document 23.8). The following documents help explore these issues about America’s use of atomic weapons in World War II.