This is what Nagasaki looked like 70 years ago, before the bomb fell:
And this is what it looked like afterwards:
The images were printed in 1946 inside the U.S. government's "strategic bombing survey," an analysis of the epochal nuclear strikes on the second Japanese city. The full report, a dispassionate narration of the events, built in part through interviews with Japanese witnesses, is worth reading.
In particular, it includes the official report of the incident by the Nagasaki Prefecture. Here's a chilling excerpt:
Within a radius of 1 kilometer from ground zero, men and animals died almost instantaneously from the tremendous blast pressure and heat; houses and other structures were smashed, crushed and scattered; and fires broke out. The strong complex steel members of the structures of the Mitsubishi Steel Works were bent and twisted like jelly and the roofs of the reinforced concrete National Schools were crumpled and collapsed, indicating a force beyond imagination. Trees of all sizes lost their branches or were uprooted or broken off at the trunk.
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