Charles Sweeney
Poor bombing visibility and an increasingly critical fuel shortage eventually forced "Bockscar" to divert from Kokura and attack the secondary target, Nagasaki. As they approached Nagasaki, the heart of the city's downtown was covered by dense cloud, and Sweeney and the plane's weaponeer, Commander Ashworth, initially decided to bomb Nagasaki using radar. However, a small opening in the clouds allowed "Bockscar's" bombardier to verify the target as Nagasaki. As the crew had been ordered to drop the bomb visually if possible, Sweeney decided to proceed with a visual bomb run. "Bockscar" then dropped "Fat Man", with a blast yield equivalent to 21 kilotons of TNT. It exploded 43 seconds later at above the ground, at least northwest of the planned aim point. The failure to drop "Fat Man" at the precise bomb aim point caused the atomic blast to be confined to the Urakami Valley. As a consequence, a major portion of the city was protected by the intervening hills, and only 60% of Nagasaki was destroyed. The bombing also severed the Mitsubishi arms production extensively and killed an estimated 35,000-40,000 people outright, including 23,200-28,200 Japanese industrial workers, 2,000 Korean slave laborers, and 150 Japanese soldiers.
Hiroshima Peace Memorial
Earlier, on 25 July, General Carl Spaatz, commander of the United States Strategic Air Forces in the Pacific, received orders to deliver a "special bomb" attack on selected cities in Japan. The first target city chosen was Hiroshima, which had an important port on southern Honshu and was headquarters of the Japanese Second General Army with 40,000 military personnel in the city. The bomb was assembled in secret and loaded on the "Enola Gay". It consisted of a uranium isotope 235 core shielded by hundreds of kilograms of lead. The bomb, code named "Little Boy", possessed a force equivalent to 15,000 tons of TNT. The plane dropped Little Boy over the city at 8:15:17 a.m. local time on 6 August 1945. Within 43 seconds of being dropped, it detonated over the city, missing its target by . Intended for the Aioi Bridge, the bomb instead exploded directly over the Shima Hospital, which was very near to the Genbaku Dome. Because the explosion was almost directly overhead, the building was able to retain its shape. The building's vertical columns were able to resist the nearly vertical downward force of the blast, and parts of the concrete and brick outer walls remained intact. The center of the blast occurred horizontally and vertically from the Dome. Everyone inside the building was killed instantly.