Fat Man is the codename for the atomic bomb that was detonated over Nagasaki, Japan, by the United States on August 9, 1945. It was the second of the only 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. It was an implosion-type weapon with a plutonium core.
Fat Man was dropped from the B-29 bomber Bockscar, piloted by Major Charles Sweeney of the 393d Bombardment Squadron, Heavy, and exploded at 11:02 AM, at an altitude of about 1,650 feet, with a yield of about 21 kilotons of TNT or 88 terajoules. Because of poor visibility due to cloud cover, the bomb missed its intended detonation point, and damage was somewhat less extensive than that in Hiroshima. An estimated 39,000 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 fire bombing raid on Tokyo.
Ivy King was the largest pure fission nuclear bomb ever tested by the United States. The bomb was tested during the Truman administration as part of Operation Ivy. This series of tests involved the development of very powerful nuclear weapons in response to the nuclear weapons program of the Soviet Union.