The United States Navy and United States Coast Guard occupational rating of gunner's mate (GM) is a designation given by the Bureau of Naval Personnel (BUPERS) to enlisted sailors who either satisfactorily complete initial Gunner's Mate "A" school training, or who "strike" for the rating by showing competence in the field of ordnance.

The Gunner's Mate "A" school is held at Naval Training Center Great Lakes, Illinois and Yorktown, VA for the USCG.

In its early years, the school was very hands-on, but it is now primarily conducted through technical educational tools, such as self-study computer-based training (CBT).

The move was made to leverage the strengths, knowledge, skills and abilities found in the two ratings to meet existing and future strategic mission needs.

Closely associated Naval occupational ratings are Fire Controlman (FC), Aviation Ordnanceman (AO), Missile Technician (MT), Mineman (MN).