80,000 people died instantly in Hiroshima, Japan, on August 6, 1945, when the first ever atomic bomb was used in war. The code name of the uranium-based bomb was Little Boy. On August 9, 1945, "an implosion-model plutonium bomb code-named Fat Man, was detonated over Nagasaki.
Hiroshima, a manufacturing center of some 350,000 people located about 500 miles from Tokyo, was selected as the first target. After arriving at the U.S. base on the Pacific island of Tinian, the more than 9,000-pound uranium-235 bomb was loaded aboard a modified B-29 bomber christened Enola G@y (after the mother of its pilot, Colonel Paul Tibbets).
The plane dropped the bomb–known as “Little Boy”–by parachute at 8:15 in the morning, and it exploded 2,000 feet above Hiroshima in a blast equal to 12-15,000 tons of TNT, destroying five square miles of the city.
Hiroshima’s devastation failed to elicit immediate Japanese surrender, however, and on August 9 Major Charles Sweeney flew another B-29 bomber, Bockscar, from Tinian. Thick clouds over the primary target, the city of Kokura, drove Sweeney to a secondary target, Nagasaki, where the plutonium bomb “Fat Man” was dropped at 11:02 that morning.
More powerful than the one used at Hiroshima, the bomb weighed nearly 10,000 pounds and was built to produce a 22-kiloton blast. The topography of Nagasaki, which was nestled in narrow valleys between mountains, reduced the bomb’s effect, limiting the destruction to 2.6 square miles.
The decision by the United States to use the atomic bomb against Japan in August 1945 is credited with ending World War II. Here is some background information about the history of the atomic bomb, by the numbers shared by CNN.