 More specifically, ADs install, maintain, and service various aircraft engine types as well as various accessories, gear boxes, related fuel systems, and lubrication systems; determine reasons for engine degradation using various test equipment; perform propeller repairs; handle and service aircraft ashore or aboard ship; and can also serve as aircrewman in various types of aircraft.In the early stages of Naval Aviation, this occupation was performed by Machinist's Mates with an aviation specialty, but qualifying for the aviation specialty required meeting the standards for the general rating as well as those required for the aviation specialty.The Aviation Machinist's Mate rating was established on July 1, 1921, along with Aviation Metalsmith, Aviation Carpenter's Mate, and Aviation Rigger.