Bombing of Hiroshima
Hiroshima was the primary target of the first nuclear bombing mission on August 6, with Kokura and Nagasaki as alternative targets. The 393d Bombardment Squadron B-29 Enola Gay, named after Tibbets' mother and piloted by Tibbets, took off from North Field, Tinian, about six hours' flight time from Japan. Enola Gay was accompanied by two other B-29s. The Great Artiste, commanded by Major Charles Sweeney, which carried instrumentation, and a then-nameless aircraft later called Necessary Evil, commanded by Captain George Marquardt, which served as the photography aircraft.
After leaving Tinian the aircraft made their way separately to Iwo Jima to rendezvous with Sweeney and Marquardt at 05:55 at 9,200 feet (2,800 m), and set course for Japan. The aircraft arrived over the target in clear visibility at 31,060 feet (9,470 m) Parsons, who was in command of the mission, armed the bomb in flight to minimize the risks during takeoff. He had witnessed four B-29s crash and burn at takeoff, and feared that a nuclear explosion would occur if a B-29 crashed with an armed Little Boy on board. His assistant, Second Lieutenant Morris R. Jeppson, removed the safety devices 30 minutes before reaching the target area.
During the night of August 5–6, Japanese early warning radar detected the approach of numerous American aircraft headed for the southern part of Japan. Radar detected 65 bombers headed for Saga, 102 bound for Maebashi, 261 en route to Nishinomiya, 111 headed for Ube and 66 bound for Imabari. An alert was given and radio broadcasting stopped in many cities, among them Hiroshima. The all-clear was sounded in Hiroshima at 00:05. About an hour before the bombing, the air raid alert was sounded again, as Straight Flush flew over the city. It broadcast a short message which was picked up by Enola Gay. It read: "Cloud cover less than 3/10th at all altitudes. Advice: bomb primary." The all-clear was sounded over Hiroshima again at 07:09.
At 08:09, Tibbets started his bomb run and handed control over to his bombardier, Major Thomas Ferebee. The release at 08:15 (Hiroshima time) went as planned, and the Little Boy containing about 64 kg (141 lb) of uranium-235 took 44.4 seconds to fall from the aircraft flying at about 31,000 feet (9,400 m) to a detonation height of about 1,900 feet (580 m) above the city.[ Enola Gay traveled 11.5 mi (18.5 km) before it felt the shock waves from the blast.
Due to crosswind, the bomb missed the aiming point, the Aioi Bridge, by approximately 800 ft (240 m) and detonated directly over Shima Surgical Clinic. It released the equivalent energy of 16 kilotons of TNT (67 TJ), ± 2 kt. The weapon was considered very inefficient, with only 1.7% of its material fissioning. The radius of total destruction was about 1 mile (1.6 km), with resulting fires across 4.4 square miles (11 km2).
Enola Gay stayed over the target area for two minutes and was ten miles away when the bomb detonated. Only Tibbets, Parsons, and Ferebee knew of the nature of the weapon; the others on the bomber were only told to expect a blinding flash and given black goggles. "It was hard to believe what we saw", Tibbets told reporters, while Parsons said "the whole thing was tremendous and awe-inspiring ... the men aboard with me gasped 'My God'". He and Tibbets compared the shockwave to "a close burst of ack-ack fire".