High Quality Content by WIKIPEDIA articles! "Fat Man" was 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 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 only 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.