The Navy Enlisted Classification (NEC) system supplements the rating designators for enlisted members of the United States Navy. A naval rating and NEC designator are similar to the Military Occupational Specialty (MOS) designators used in the U.S. Army and U.S. Marine Corps and the Air Force Specialty Code (AFSC) used in the U.S. Air Force. For example, a person holding the MM-3385 is a nuclear-trained machinist's mate for surface ships, and a person with an MM-3355 is a nuclear-trained machinist's mate for submarines.