Thin Man (nuclear bomb) and the name came from the Dashiell Hammett detective novel "The Thin Man" and series of movies by the same name. The "Fat Man" bomb would be round and fat and was named after Sydney Greenstreet's character in "The Maltese Falcon". "Little Boy" would come last and be named only to contrast to the "Thin Man" bomb. Oppenheimer assembled a team at the Los Alamos Laboratory to work on plutonium gun design that included senior engineer Edwin McMillan and senior physicists Charles Critchfield and Joseph Hirschfelder. Critchfield had been working with sabots, which Oppenheimer believed would be required by the
Thin Man (nuclear bomb) materials react more rapidly and therefore more completely. It was decided that the plutonium gun would receive the bulk of the research effort, since it was the project with the least amount of uncertainty involved. It was assumed that the uranium gun-type bomb could be more easily adapted from it. The gun-type and implosion-type designs were codenamed "Thin Man" and "Fat Man" projects respectively. These code names were created by Robert Serber, a former student of Oppenheimer's who worked on the Manhattan Project. He chose them based on their design shapes; the "Thin Man" would be a very long device,