The Order is Given

When the Japanese military ignored the Potsdam Declaration's threat of "prompt and utter destruction," Groves drafted the orders to use the bomb and sent them to General Carl Spaatz, commander of air forces in the Pacific. Upon approval by Army Chief of Staff George C. Marshall, Secretary of War Stimson and President Truman, the order to drop Little Boy on Hiroshima had officially been given.

General Handy's Bombing Order
General Handy's Bombing Order