The night the American B-29 warplanes came, Ryohei Nakane had been enriching uranium for Japan's "super bomb."
By the next morning -- April 13, 1945 -- all that remained of his samples and his laboratory at Riken Institute was charred, splintered wood and broken glass.
For nearly six decades, historians have been unable to solve one of the mysteries of Japan's World War II A-bomb project: How close were Japanese scientists to building the bomb before the U.S. air raid stopped them?
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