Thursday, August 05, 2010
At approximately 8:15 a.m. 6th of August, 1945, a USAAF B-29 bomber of the 393rd Bombardment Squadron, 509th Composite Group, victor number 82, having made a six hour flight from its base on the island of Tinian dropped a gun-type fission weapon containing 60 kilograms of uranium-235 from its bomb bay over the city of Hiroshima located in the deltas of the southwest of Honshu.
Due to crosswinds the bomb drifted past its aiming point by about 800 feet. At an altitude of 1900 feet, 43 seconds after being released from the aircraft bomb bay, a sub-critical hollow projectile weighing 39 kg, 7 inches long with a diameter of 6 1/4 inches made of stacked rings was fired by a cordite charge down a 1.8 meter barrel at 300 meters per second towards a 26 kg spike of uranium-235, also made of stacked up rings. The projectile became critical after travelling only 0.3 millimeters. As the projectile moved to envelop the spike super-criticality had already occurred. Once the projectile and the spike became a single assembly a fission reaction took place.
1.38 percent of the material fissioned making this one of the least efficient bombs ever made. In that instant, 30 percent of the population of Hiroshima (about 70/80000 people) were killed instantly while another 70,000 were injured. The blast radius was estimated at 1.6 km with 12 square km of the city destroyed. 90 percent of doctors and over 90 percent of nurses were either killed or injured in the blast. Hospitals, although still standing were destroyed through their interiors. Medical supplies were gone. Fire fighting was non-existent. It took over 30 hours to organize any kind of coordinated assistance and rescue.
Hiroshima had just become the first ever target in the first ever nuclear war.