[chimera]

The gun-assembly 235U bomb was named “Little Boy”. The “Fat Man” was the plutonium weapon used at Nagasaki. Check out their form factors for the naming conventions. The Trinity test article was The Gadget, since it was not yet weaponized.

[RayChuang88]

If I remember correctly, the device tested at the Trinity site had the same fissile material shape as the Fat Man bomb, but they surrounded it with a lot of extra material and test sensors because nobody at Los Alamos knew if this device would actually work. But once the bomb was successfully tested on July 16, 1945, they could assemble Fat Man with assurances it would actually work.