What did the World War 2 naval rank MOMM C2 mean?

In World War II, the naval rank "MOMM C2" stood for Machinist's Mate, First Class (MOMM), with "C2" indicating the specific classification or level of expertise within that rating. Machinist's Mates were responsible for operating and maintaining machinery, including engines and propulsion systems on ships. The "C2" designation typically denoted a level of proficiency or specialization within the Machinist's Mate rating.