Gunner ' s mate The United States Navy 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 , when " striking " you do not need to be a seaman , but you do need to be one of the 3 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 ; Information Specialist third class ( IS3 ) cross rates to Gunner ' s Mate that sailor is now a Gunner ' s Mate third class ( GM3 ) . The Gunner ' s Mate " A " school is held at Naval Training Center Great Lakes , Illinois . While the school was originally very hands - on , it is now primarily conducted through self - study computer - based training ( CBT ) . The training focuses on the operation , maintenance , and troubleshooting of naval guns , missile launchers , and torpedoes as well as a strong emphasis on basic explosive s , guidance and tracking systems , small arms , Naval ammunition classification , and safety . Upon completion of this basic training , enlisted members often continue on to a specialized " C " school , where they learn a particular weapons system . A GM will specialize in weapons such as the M500 shotgun , M60 machine gun , M14 rifle , M2 Browning machine gun , M9 pistol , M11 pistol , M16 rifle , M240 machine gun , M203 grenade launcher , M79 grenade launcher , M1911 pistol , M1 Garand , Mk 19 grenade launcher , Mk 18 Mod 0 Carbine Rifle , 5 " / 54 caliber Mark 45 gun , M242 Bushmaster chain gun , Vertical launching system , Missiles , , pyrotechnics , hand grenade s , non - lethal weapons , force protection & anti - terrorism , as well as operating shooting range s , armories , and the storage and issue of ammunition . On February 26 , 2007 the Chief of Naval Operations approved the merger of the gunner ’ s mate ( GM ) and torpedoman ’ s mate ( TM ) ratings into the GM rating . The move was made to leverage the strengths , knowledge , skills and abilities found in the two ratings to meet mission needs now and in the future . “ The training Sailors receive after basic training for their ratings on an apprentice level has been the same for both gunner ' s and torpedoman ' s mates , ” said Senior Chief Torpedoman ' s Mate Sherry Secrease of the Navy Personnel Command . “ This makes the merger easier to accomplish . ” The Gunner ' s Mate rating is primarily surface warfare - based . Closely associated Naval occupational ratings are Fire Controlman ( FC ) , Aviation Ordnanceman ( AO ) , Weapons Technician ( WT ) , Missile Technician ( MT ) , Mineman ( MN ) , and Machinist ' s Mate ( Weapons ) ( MMW ) . The Gunner ' s Mate rating is one of the original ratings created as a result of the Naval Armament Act of 1797 . The others include Boatswain ' s Mate ( BM ) , Quartermasters ( QM ) and Master - at - Arms ( MA ) . The rating is also among the top five source ratings for enlisted Naval Special Warfare candidates .