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Atomic bombings of Hiroshima and Nagasaki
August 6 and 9, 1945· Event· Tools, energy & materials
Well documentedSolid records, physical evidence or scientific consensus.
In August 1945 the United States dropped atomic bombs on two Japanese cities, the only nuclear weapons ever used in war.
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On August 6 a uranium bomb ('Little Boy') destroyed central Hiroshima; on August 9 a plutonium bomb ('Fat Man') struck Nagasaki. Estimates vary, but roughly 150,000 to 246,000 people had died within months, most of them civilians, including many Korean laborers and residents. Many survivors, the hibakusha, later suffered radiation illness and higher cancer rates. The Soviet Union declared war on Japan on August 8, and Japan announced its surrender on August 15, which also ended its rule over Korea.
Why it mattered
The bombings came days before Japan's surrender and opened the nuclear age. No nuclear weapon has been used in war since, a restraint many link to their horror.
How we know
The US Strategic Bombing Survey (1946), long-term health studies of survivors by the Radiation Effects Research Foundation, city records, and testimony kept at both cities' peace museums.
Still unknown or debated
Whether the bombs were needed to end the war, and how much the Soviet declaration of war mattered, remains one of history's most debated questions.
Connections (2)
▸Manhattan Project built the bombs used in the Atomic bombings of Hiroshima and NagasakiWell documented
The connection
The project produced two bomb designs: a uranium 'gun' type that fired one piece of uranium-235 into another, and a plutonium implosion type, tested at Trinity in July 1945. With Germany already defeated in May, the bombs were used against Japan, one of each design in August 1945.
When and how
Built at Los Alamos, Oak Ridge and Hanford; B-29 bombers flew from Tinian in the Mariana Islands; President Truman approved their use.
How we know
Military orders, Target Committee minutes, flight records and the Smyth Report document the decision and the missions.
Debates and open questions
Some project scientists, in the June 1945 Franck Report, urged a demonstration instead of use on cities; whether such alternatives were realistic is still argued.
▸Atomic bombings of Hiroshima and Nagasaki opened the nuclear arms race behind the Space RaceMostly agreed
The connection
The bombings showed the world what nuclear weapons could do. After the Soviet Union tested its own bomb in 1949, both sides wanted missiles that could carry warheads across oceans. The Soviet R-7, the first intercontinental missile, launched Sputnik in 1957, and the missile contest became a space contest.
When and how
First Soviet bomb test, August 1949; Soviet R-7 missile, 1957; US Atlas and Titan missiles from 1959, both later used to launch astronauts.
How sure are we?
Rocket histories show early space launchers were adapted missiles, and officials on both sides tied space programs to missile strength and prestige.
Debates and open questions
Historians weigh how much the race was military rivalry versus prestige and propaganda; Kennedy himself said privately in 1962 that he was not that interested in space.