gyrene

Uncertain. First attested 1894 in a list of United States Naval Academy slang, where it remained in use at least until 1925. Widely adopted during the Second World War. Often stated to be a blend of GI + marine, but early uses antedate both the widespread adoption of the term GI (c. 1910) and its use to denote individuals (c. late 1930s). Possibly related to Royal Navy slang gerine (“a marine”), though gyrene antedates it in print. gerine is sometimes given as a clipping of tangerine, in reference to the color of the tunics worn by the Royal Marine Light Infantry, but U.S. Marines' uniforms did not have such a color.

来源：wiktionary