On July 26, 1945 the United States issued an ultimatum to Japan. The ultimatum demanded unconditional surrender, or Japan would face complete destruction. While there was no mention of a new Super Weapon, the ultimatum was very strongly worded. The Japanese did not surrender, and on August 6, 1945 the crew of the Enola Gay dropped the atomic bomb on Hiroshima. The blast is pictured above. The picture was taken from the tail of the B-29 Superfortress that dropped the bomb.
The decision to drop the bomb is debated to this very day.