In three days, two bombs killed up to 246,000 people and ended a world war. The decision to drop them — and whether it was necessary — is still argued by historians today.
On August 6, 1945, a B-29 named Enola Gay dropped 'Little Boy' — a uranium bomb — on Hiroshima, Japan. The explosion instantly killed an estimated 80,000 people and destroyed 5 square miles of the city. Three days later, 'Fat Man,' a plutonium bomb, fell on Nagasaki, killing 40,000 immediately. By the end of 1945, total deaths from both cities combined reached between 150,000 and 246,000 — from the blasts, fires, and radiation.
The Manhattan Project that built these weapons had employed 130,000 people at its peak, cost $2 billion (roughly $30 billion today), and was kept secret from the American public, most of Congress, and even Vice President Harry Truman until FDR died and Truman became president. He learned of it 12 days after taking office. He had 16 days to decide whether to use it.
The strategic context was desperate by any measure. Japan had rejected surrender demands. Allied planners projected that an invasion of the Japanese home islands — Operation Downfall — would cost between 250,000 and 1 million American casualties and multiple times that number of Japanese. Conventional bombing had already destroyed 64 Japanese cities, killing hundreds of thousands. The atomic bomb was seen as a way to end the war without the invasion.
Hiroshima was chosen partly because it had been left relatively undamaged by conventional bombing, giving a clear measure of the weapon's effect. Nagasaki was actually a secondary target — the primary target, Kokura, was hidden under clouds that morning. The bombardier couldn't see the aiming point and turned for Nagasaki instead. Kokura survived by accident of weather.
Japan announced its surrender on August 15 — nine days after Hiroshima. Emperor Hirohito's radio address, the first time most Japanese had heard his voice, said Japan was surrendering because the enemy had 'begun to employ a new and most cruel bomb.' The formal surrender ceremony was held on September 2, 1945, on the deck of the USS Missouri in Tokyo Bay, ending World War II.
The debate over the bombings has never fully resolved. Proponents argue they ended the war quickly and saved millions of lives that an invasion would have cost. Critics point to the massive civilian death toll, question whether Japan was already near surrender, and argue the bombings were partly intended to intimidate the Soviet Union as the Cold War began. The Hiroshima and Nagasaki bombings remain the only use of nuclear weapons in warfare in history.