The United States Navy occupational rating of gunner's mate (GM) was 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. When "striking" you do not need to be a seaman, but you do need to be one of the three undesignated rates; Fireman (FN), Seaman (SN), or Airman (AN). You can also "cross rate" to Gunner's Mate. "Cross rating" is where you cross from your current rating to another rating of your choice if your ASVAB scores are high enough and the Navy has any open slots for that rate; for example, Intelligence Specialist third class (IS3) can cross rate to a Gunner's Mate, then that sailor becomes a Gunne