It was the second of two nuclear weapons to be used in warfare to date (the other being "Little Boy"), and its detonation caused the third man-made nuclear explosion. The name also refers more generically to the early nuclear weapon designs of U.S. weapons based on the "Fat Man" model. It was an implosion-type weapon with a plutonium core, similar to "The Gadget", the experimental device detonated less than a month earlier on July 16 at Alamogordo Air Field, New Mexico. "Fat Man" was possibly named after Winston Churchill, though Robert Serber said in his memoirs that as the "Fat Man" bomb was round and fat, he named it after Sydney Greenstreet's character of "Kasper Gutman" in The Maltese Falcon.
The original target for the bomb was the city of Kokura, but obscuring clouds necessitated changing course to the alternative target, Nagasaki. "Fat Man" was dropped from the Boeing B-29 bomber Bockscar, piloted by Major Charles Sweeney of the 393rd Bombardment Squadron, Heavy, and following a 43-second duration free fall, exploded at 11:02 AM (JST), at an altitude of about 1,650 feet (500 m), with a yield of about 21 kilotons of TNT or 88 terajoules. The Mitsubishi-Urakami Ordnance Works, the factory that manufactured the type 91 torpedoes released in the attack on Pearl Harbor, was destroyed in the blast. Because of poor visibility due to cloud cover, the bomb missed its intended detonation point by almost two miles, and damage was somewhat less extensive than that in Hiroshima.
An estimated 40,000 people were killed outright by the bombing at Nagasaki, and a further 25,000 were injured. Thousands more died later from related blast and burn injuries, and hundreds more from radiation illnesses from exposure to the bomb's initial radiation. The bombing raid on Nagasaki had the third highest fatality rate in World War II after the nuclear strike on Hiroshima and the March 9/10 1945 Operation Meetinghouse firebombing raid on Tokyo. For more infoamtion of the Fat Man please click here.