Less than two percent of the uranium reacts, and a city disappears
What happened
Facing a Japanese government that showed no sign of surrender despite Germany's defeat and an estimated 300,000 civilian deaths from conventional bombing and starvation, President Truman approved the use of the atomic bomb rather than risk an invasion projected to be costlier than Okinawa, where the United States had already lost more than 12,000 dead against a far smaller, more isolated island. On 6 August, the B-29 Enola Gay dropped the uranium bomb Little Boy over Hiroshima; it detonated with the force of over 15,000 tons of TNT, and although less than two percent of its uranium actually achieved fission, ground temperatures reached 7,000 degrees Fahrenheit in under a second, killing at least 80,000 people instantly. Reverend Kiyoshi Tanimoto, two miles from the blast, described a sheet of sun crossing the sky before the shockwave collapsed the house he was standing near. Three days later, the plutonium bomb Fat Man, redirected to Nagasaki after cloud cover obscured its intended target of Kokura, killed between 40,000 and 75,000 more.
Why it matters
These remain the only nuclear weapons ever used in war, and the vast destructive power packed into such a small fraction of actually-reacting material is exactly what made the weapon strategically decisive: a single bomb, dropped by a single aircraft, could now inflict the destruction that had previously required a fleet of hundreds.
How we know
US military timeline logs from the Enola Gay and Bockscar missions, combined with Japanese casualty surveys conducted in the bombings' aftermath and firsthand survivor accounts like Tanimoto's, corroborate both the bombs' immediate mechanics and their human toll.
Sources
- The National WWII Museum. The Most Fearsome Sight: The Atomic Bombing of Hiroshima · Reputable sourcenationalww2museum.org · The domain "nationalww2museum.org" is on our Reputable source registry. · Link is live and its text matches the event's key terms (Jul 2026)
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