President Harry Truman endlessly debated the question with his advisors–should the United States use the bomb against Japan? The only other option, Groves argued, was to invade the country, a mission that threatened the loss of over one million men. While not everyone agreed that the losses would be this high, they did agree that even 35,000 losses (a more conservative estimate) were too many to risk.
A compromise was proposed: perhaps the United States could give Japanese leaders a demonstration of the bomb's power in an uninhabited area. Surely, these reluctant physicists and politicians argued, this would be enough to convince the Japanese that they should surrender. But Oppenheimer–as well as Groves and Truman–objected to this plan, afraid that the Japanese would refuse to back down, and the element of surprise would be lost.
Eventually Truman decided that the bomb would be used against Japan. In fact, historian Martin J. Sherwin has argued that the issue was never seriously in question and that it was always assumed that the atomic bomb would be used to end the war. Oppenheimer agreed, noting, "the decision was implied in the project."
On August 6, 1945, a B-29 bomber, the Enola Gay, dropped the Little Boy bomb on the city of Hiroshima, population 400,000. The city had been evacuated in anticipation of attack, leaving only 300,000 residents – the majority of whom were civilians. In a single instant, the bomb destroyed 70,000 buildings–over ninety percent of the city's structures. One hundred thousand people died instantly, or within a couple days of the explosion. At least 100,000 more died within five years. Three days later, on August 9, the United States dropped a second bomb, the Fat Man. This bomb was dropped on the Japanese city of Nagasaki, and it killed another 100,000 people.
Five days later, the Japanese Emperor Hirohito announced his surrender.
The majority of the country supported the dropping of the bomb on Japan, as did the majority of the scientists who worked on the project. Oppenheimer was initially thrilled to hear that the bombs had worked, and it was only later that he began to fear the consequences of a nuclear world.