Hiroshima and Nagasaki: the Only Nuclear Attacks in History

On 6 and 9 August 1945 the United States dropped nuclear bombs on the Japanese cities of Hiroshima and Nagasaki — the only two times nuclear weapons have ever been used against people. Japan surrendered on 15 August, ending the Second World War.

Mushroom cloud over Nagasaki — The mushroom cloud over Nagasaki rose roughly 18 km into the sky on 9 August 1945.

Hiroshima, 6 August 1945

At 8:15 a.m. the B-29 Enola Gay released Little Boy, a gun-type uranium bomb of roughly 15 kilotons, which detonated about 580 metres above the city centre. The airburst height was chosen to maximise blast damage — exactly the trade-off you can explore with the airburst settings in the simulator. Within a radius of about two kilometres nearly every building was destroyed or burned; a firestorm followed. An estimated 70,000 people died immediately, and by the end of 1945 the toll had reached roughly 140,000 out of a population of about 350,000.

Nagasaki, 9 August 1945

Three days later Fat Man, an implosion plutonium bomb of about 21 kilotons — the same design proven at Trinity — was dropped on Nagasaki, a secondary target chosen when clouds obscured Kokura. Though the bomb was more powerful than Little Boy, the hilly terrain confined the destruction to the Urakami valley: roughly 40,000 people died at once and about 70,000 by the end of the year. The contrast between the two cities remains the clearest historical lesson in how terrain changes nuclear effects — something no idealised model fully captures.

Hiroshima in ruins after the bombing — The centre of Hiroshima reduced to rubble, 1945.

What killed people

Studies of the survivors show the deaths came from the combination of effects described on our effects page: the thermal flash caused fatal burns out to about 3.5 km, the blast collapsed buildings and drove debris, fires merged into firestorms, and the prompt radiation delivered lethal doses within roughly 1.3 km. Tens of thousands who survived the day died in the following weeks from burns and radiation sickness — a pattern of delayed death that shocked even the bombs' creators. The roughly 94,000 registered survivors (hibakusha) studied over their lifetimes showed measurably elevated cancer rates, and their data underpin radiation safety standards worldwide to this day.

Blast radius comparison diagram — Blast radius grows with the cube root of yield: an 800 kt warhead reaches far beyond the 15 kt Hiroshima bomb.

The bombs in today's terms

By modern standards Little Boy was small. A single warhead on today's ballistic missiles typically yields 300–800 kilotons — twenty to fifty Hiroshimas. Load the Hiroshima preset over your own city in the simulator, then replace it with a modern 800-kt warhead, and the difference needs no commentary. More context: how nuclear weapons work and the world's arsenals today.