Little Boy was the codename for the type of atomic bomb dropped on Hiroshima on August 6, 1945 by the Boeing B-29 Superfortress Enola Gay, piloted by Colonel Paul W. Tibbets, Jr., commander of the 509th Composite Group of the United States Army Air Forces. It was the first atomic bomb to be used as a weapon. The Hiroshima bombing was the second artificial nuclear explosion in history, after the Trinity test, and the first uranium-based detonation. Approximately 600 to 860 milligrams (9.3 to 13.3 grains) of matter in the bomb was converted into the energy of heat and radiation. It exploded with an energy of 16 kilotons of TNT (67 TJ).