Nagasaki
On the day of the nuclear strike (August 9, 1945) the population in Nagasaki was estimated to be 263,000, which consisted of 240,000 Japanese residents, 10,000 Korean residents, 2,500 conscripted Korean workers, 9,000 Japanese soldiers, 600 conscripted Chinese workers, and 400 Allied POWs. That day, the Boeing B-29 Superfortress "Bockscar", commanded by Major Charles Sweeney, departed from Tinian's North Field just before dawn, this time carrying a plutonium bomb, code named "Fat Man". The primary target for the bomb was Kokura, with the secondary target being Nagasaki, if the primary target was too cloudy to make a visual sighting. When the plane reached Kokura at 9:44 a.m. (10:44 a.m. Tinian Time), the city was obscured by clouds and smoke, as the nearby city of Yawata had been firebombed on the previous day. Unable to make a bombing attack on visual due to the clouds and smoke and with limited fuel, the plane left the city at 10:30 a.m. for the secondary target. After 20 minutes, the plane arrived at 10:50 a.m. over Nagasaki, but the city was also concealed by clouds. Desperately short of fuel and after making a couple of bombing runs without obtaining any visual target, the crew was forced to use radar in order to drop the bomb. At the last minute, the opening of the clouds allowed them to make visual contact with a racetrack in Nagasaki, and they dropped the bomb on the city's Urakami Valley midway between the Mitsubishi Steel and Arms Works in the south, and the Mitsubishi-Urakami Ordnance Works in the north. 53 seconds after its release, the bomb exploded at 11:02 a.m. at an approximate altitude of 1,800 feet.
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.