There was a total of more than 800 B-29 bomber in Tinian and Saipan. They can carry several tons of bombs on a flight of more than two thousand kilometers, bombing of Tokyo, Nagoya, Kobe, dozens of rounds down, the 65 cities have been the almost complete absence of buildings.
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BUT
However, the tragedy of Hiroshima did not make Japan agreed to accept the Potsdam ultimatum immediately, unconditional surrender. They tried to cover up the truth of Hiroshima, claiming that a meteorite fall in Hiroshima city. And that the U.S. has only one atomic bomb, also put their hopes in the Soviet Union to mediate.
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Finally...
In August 15, 1945, the emperor of Japan issued the surrender.
In September 2, 1945, in Tokyo Bay, "Missouri" on the deck of the battleship, the Japanese Foreign Minister Mamoru Shigemitsu and chief of staff Umezu Meijiro signed the surrender document. Signing time is four past nine. Then, the southwest Pacific theater commander Douglas Macarthur signature. USA, China, Britain and the Soviet Union and other countries at war with Japan accepted the Japanese surrender.