Atomic bombings of Hiroshima and Nagasaki

On 6 and 9 August 1945 the United States dropped atomic bombs on the Japanese cities of Hiroshima and Nagasaki, in the final weeks of World War II. The bombs killed an estimated 150,000 to 246,000 people by the end of 1945, most of them civilians, and destroyed much of both cities. Japan announced its surrender days later. They remain the only uses of nuclear weapons in war.

Fearing that Nazi Germany might build an atomic bomb, the United States, with British and Canadian participation, set up a secret programme, the Manhattan Project, in 1942. Directed by General Leslie Groves, with the physicist J. Robert Oppenheimer leading the weapons laboratory at Los Alamos in New Mexico, it employed well over 100,000 people at its peak. Two designs were developed: a gun-type bomb using uranium-235 and a more complex implosion bomb using plutonium. The plutonium design was tested in the New Mexico desert on 16 July 1945, the Trinity test.

By mid-1945 Germany had surrendered, but the war with Japan continued. American bombers had already burned large parts of Japanese cities with incendiary raids, and plans were being made to invade the home islands. President Harry Truman, who had taken office in April, approved the use of the bomb. A committee chose targets among cities not yet heavily bombed, and Secretary of War Henry Stimson had the historic city of Kyoto removed from the list. On 26 July the Allies issued the Potsdam Declaration, demanding Japan's unconditional surrender and warning of prompt and complete destruction; the Japanese government did not accept it.

Early on the morning of 6 August 1945, the B-29 bomber Enola Gay, flying from the island of Tinian, dropped the uranium bomb known as Little Boy on Hiroshima, a city with an army headquarters and a large garrison. It exploded above the city centre with a force equivalent to roughly 15,000 tonnes of TNT. The blast and firestorm destroyed most buildings within about two kilometres. Estimates of deaths by the end of 1945 range from about 90,000 to 166,000.

On 8 August the Soviet Union declared war on Japan, invading Manchuria the next day. On 9 August a second B-29, Bockscar, set out to bomb Kokura, but finding it obscured by haze and smoke it turned to its secondary target, Nagasaki. The plutonium bomb, Fat Man, was more powerful, but hills confined much of the damage to one valley. Between about 60,000 and 80,000 people died by the end of the year.

On 15 August Emperor Hirohito announced Japan's acceptance of the Allied terms in a radio broadcast, and the formal surrender was signed on 2 September 1945. Historians continue to debate the relative weight of the bombs and of the Soviet entry into the war in Japan's decision.

Many people died in the following months and years from burns, injuries and radiation sickness, and survivors, known in Japan as hibakusha, faced higher rates of cancer and long-term social discrimination. Many Koreans, a large number of them conscripted labourers, were among the victims, as were Allied prisoners of war. Whether the bombings were justified has been argued since 1945. Supporters say they ended the war quickly and saved the lives that an invasion would have cost; critics argue that Japan was close to surrender, that alternatives existed, and that deliberately targeting cities full of civilians was morally indefensible. Both cities were rebuilt, and Hiroshima's Peace Memorial Park and the ruined dome at its edge became symbols of the campaign against nuclear weapons.

Our 1938 map shows the Empire of Japan after its invasion of China, and our 1945 map shows Japan at the end of the war.