What US president decided to drop the atomic bomb during World War 2?
the 33rd President of the United States, Harry S Truman from Missouri.
Franklin D. Roosevelt authorized the Manhattan Project, the massive undertaking by the US, Canada and Great Britain that created the first atomic "pile," the first sustained, controlled, man-made nuclear fission reaction, and the first atomic explosive device. Implicit in his authorization is his intent to use it against a foreign enemy. Roosevelt died just three months before the Trinity "shot," the first detonation of an atomic warhead in the New Mexico desert in July 1945.
Harry S. Truman, FDR's vice president, had been essentially kept in the dark with regard to the atomic bomb until Roosevelt's death. Once he became president in April 1945, however, he was quickly apprised of the status of the bomb project, and he insisted on daily reports about it. After the Trinity "shot," Truman took the decision to use the two remaining bombs against Japan.