Learn about the first atomic explosion in history as well as some of the circumstances that led to the decision to use the bomb in this clip from The Bomb. Vice-President Harry Truman was never told about the secret bomb project. When President Roosevelt died suddenly in April 1945, Truman found himself responsible for the bomb. By July 1945, the first bomb was ready to test, but the scientists had no idea if it would work or what would happen if it did. People who were there that night were awed and amazed by its power. Few realized at that moment how profoundly the bomb would change the world.