On August 6th, 1945 a weapon unlike any other before was unleashed on the Japanese city of Hiroshima. Four days later, the Japanese surrendered having been subjected to horrors and devastation previously unknown and unimaginable. But beyond the horror and human toll, real scientific questions remained unanswered. In 1945, a team of scientists and experts from the Manhattan Project was ordered by President Truman to investigate the facts of what really happened when the atomic bomb exploded over Hiroshima. National Geographic reveals the incredible science behind what happened moment by moment in the .