The five-ton plutonium bomb plunged toward the city at 614 miles per hour. Forty-seven seconds later, a powerful implosion forced its plutonium core to compress from the size of a grapefruit to the size of a tennis ball, generating a nearly instantaneous chain reaction of nuclear fission. With colossal force and energy, the bomb detonated a third of a mile above the Urakami Valley and its thirty thousand residents and workers, a mile and a half north of the intended target. At 11:02 a.m., a superbrilliant flash lit up the sky—visible from as far away as Ōmura Naval Hospital more than ten miles
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