What was the code name of the making of the atomic bomb Fat Man?

The code name for the development of the atomic bomb known as "Fat Man" was part of the Manhattan Project. Specifically, Fat Man was developed at the Los Alamos Laboratory under the direction of J. Robert Oppenheimer. The bomb used a plutonium core and was the second atomic bomb dropped on Japan, following "Little Boy," which was a uranium-based bomb. Fat Man was detonated over Nagasaki on August 9, 1945.