"Fat Man" is the code name for the atomic bomb that was detonated over Nagasaki, Japan, by the United States on August 9, 1945, at 11:02 a.m. (JSP). It was the second of the only two nuclear weapons to be used in warfare and was 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. [1]