This bomb was dropped by a B-29 bomber called “Enola Gay”. The first atomic bomb was to be used as a weapon. "Little Boy", its code name, was dropped on the flat ground of Hiroshima. The bomb vaporized buildings and killed thousands of people. The bomb exploded 580 meters above central Hiroshima at 8:15 a.m. local time, with an estimated power of 15 kilotons. The height of the airburst was chosen to maximize the extent of the immediate effects and minimize residual radiation fallout. Individuals at ground zero received combined gamma and neutron doses of approximately 80,000 rad, which are used to measure radiation. Having been immediately fatal, the thermal flash caused fires that grew into a storm-like fire, razing much of the city. The flash, explosion and rapid radiation killed most people within 0.8 miles of the ground.