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Atomic bombings of Hiroshima and Nagasaki
August 6 and 9, 1945· Event· Asia
Well documentedSolid records, physical evidence or scientific consensus.
The US atomic bombings of Hiroshima (August 6, 1945) and Nagasaki (August 9), the only nuclear weapons ever used in war.
See it on the History map →What happened
The bombs came from the Manhattan Project, a secret US-led effort with British and Canadian help. A B-29 named Enola Gay dropped a uranium bomb, 'Little Boy', on Hiroshima; a plutonium bomb, 'Fat Man', hit Nagasaki three days later. Each destroyed much of its city in seconds. By the end of 1945 about 140,000 had died in Hiroshima and about 74,000 in Nagasaki, many from burns and radiation; estimates vary. Thousands of Korean laborers were among the dead.
Why it matters
Japan surrendered within days, and the nuclear age began: an arms race, deterrence strategy, and a taboo on their use in war that has held ever since.
How we know
US military and scientific records, Japanese casualty surveys, the 1946 US Strategic Bombing Survey, photographs, and testimony from survivors, called hibakusha.
Still debated
Whether the bombs were needed to end the war without an invasion, or whether the Soviet entry mattered more, is one of history's most argued questions.
Connections (4)
▸Atomic bombings of Hiroshima and Nagasaki helped end World War IIDebated
The connection
Japan surrendered within days of the bombings, and Emperor Hirohito's August 15 broadcast cited a 'new and most cruel bomb'. But the Soviet Union also declared war on August 8 and invaded Manchuria, ending Japan's hope of Soviet mediation. Historians disagree on which shock mattered more, and whether surrender would have come without the bombs.
When and how
Tokyo's Supreme War Council, August 9–14, 1945; the emperor broke a deadlock in favor of surrender, despite an attempted coup by army officers.
How sure are we?
Japanese leaders' records and postwar interviews, US intercepts, and the emperor's broadcast support both the bombs and the Soviet entry as factors.
Debates and open questions
Tsuyoshi Hasegawa argues the Soviet entry was decisive; Richard Frank stresses the bombs. Whether an invasion would otherwise have been needed is unresolved.
▸Atomic bombings of Hiroshima and Nagasaki opened the nuclear age of the Cold WarWell documented
The connection
The bombs showed the world a weapon that could destroy a city in one blow. The Soviets, who had spies inside the Manhattan Project, raced to test their own bomb in 1949. An arms race followed, with hydrogen bombs and missiles, and deterrence through 'mutually assured destruction' is widely credited with keeping the superpowers from fighting directly.
When and how
The Soviet test came in Kazakhstan on August 29, 1949; the US tested a hydrogen bomb in 1952 and the USSR in 1953–55.
How we know
Declassified weapons programs, espionage cases such as Klaus Fuchs's, and arsenal data showing world stockpiles peaked at about 70,000 warheads in 1986.
Debates and open questions
Some historians argue the bombings were partly meant to intimidate the Soviets, a view called 'atomic diplomacy'; how much that motive mattered is debated.
▸Atomic bombings of Hiroshima and Nagasaki showed what was at stake in the Cuban Missile CrisisMostly agreed
The connection
Hiroshima and Nagasaki showed what a single bomb could do to a city. By 1962 both superpowers had hydrogen bombs tens to thousands of times more powerful. Leaders on both sides understood the stakes, and that knowledge pushed Kennedy and Khrushchev to look for a way out rather than escalate.
When and how
Japan, August 1945; then Washington and Moscow, October 1962, where Kennedy and Khrushchev exchanged letters about avoiding catastrophe.
How sure are we?
Khrushchev's letters to Kennedy and the White House tapes refer directly to nuclear devastation; the hotline and test-ban treaty followed.
Debates and open questions
Whether nuclear deterrence kept the peace in 1962, or the world was simply lucky, is still debated.
▸Attack on Pearl Harbor began the US–Japan war that ended after Atomic bombings of Hiroshima and NagasakiWell documented
The connection
Pearl Harbor began nearly four years of Pacific war: Midway in 1942, island-hopping campaigns, and firebombing of Japanese cities. Iwo Jima and Okinawa in 1945 were very costly, and planners feared huge losses invading Japan. President Truman approved using the new atomic bombs, aiming to force surrender without an invasion.
When and how
The Pacific, December 1941 to August 1945; Truman approved the bombings after the first atomic test in New Mexico on July 16, 1945.
How we know
Truman's August 6 statement linked them directly: 'The Japanese began the war from the air at Pearl Harbor. They have been repaid many fold.'
Debates and open questions
How large the projected invasion casualties really were, and whether postwar accounts inflated them to justify the bombings, is debated.