"Thin Man" was the code name for a proposed plutonium-fueled gun-type nuclear bomb that the United States partially developed during the Manhattan Project. Its development was abandoned in 1944 after
"Thin Man" plutonium gun test casings
Robert Serber claims that the original gun-type design, Thin Man, was named after the series of noir films based on the work of Dashiell Hammett that were popular in the 1930s and 1940s.
"Thin Man" plutonium gun test casings at Muroc Army Airfield, as part of Project Alberta in the Manhattan Project. "Fat Man" casings can be seen behind them.
A prototype of the "Thin Man" gun being tested at Anchor Ranch, at Los Alamos
Little Boy was a type of atomic bomb created by the Manhattan Project during World War II. The name is also often used to describe the specific bomb used in the bombing of the Japanese city of Hiroshi
Thin Man (nuclear bomb)
…and series of movies by the same name. The Fat Man would be round and fat and was named after Sydney Greenstreet's character in The Maltese Falcon. The Little Boy uranium gun-type design came later and was named only to contrast with the Thin Man. Los Alamos's Thin Man and Fat Man code names were adopted by the…
Little Boy target case (left) attached to a gun tube at Anchor Ranch, Los Alamos, used for testing purposes. Compare with a similar image of the Thin Man internal components.
As part of Project Alberta, Commander A. Francis Birch (left) assembles the combat unit (L-11) while physicist Norman Ramsey watches. This is one of the rare photos where the interior of the bomb can be seen, with the fuzing units and battery boxes visible, attached around the gun tube.