Only hours after Little Boy was dropped, President Truman released a public statement informing the world of the destruction of Hiroshima by the atomic bomb. Truman further pledged to continue bombing Japan with the new weapon if they did not surrender. The Japanese leaders at first thought Truman was only making threats. Because all communications with Hiroshima had been cut off, they had not yet received news of what had happened to the city. When they did learn of the utter destruction of Hiroshima, the Japanese leadership decided to continue fighting. On August 8, 1945, the Soviet Union declared war on Japan and began pushing the Japanese forces out of Manchuria.

Three days after Hiroshima, a B-29 bomber took off from Tinian. It was carrying the ten-thousand-pound Fat Man plutonium bomb that was identical to the one that had exploded in the Trinity Test. Captain...