Aviation Machinist's Mates (abbreviated as AD) are United States Navy aircraft engine mechanics that inspect, adjust, test, repair, and overhaul aircraft engines and propellers.

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.

[2] [3] ADs may be assigned to sea or shore duty any place in the world, so their working environment varies considerably.

ADs must have good memories and the ability to do repetitive tasks, perform detailed work, and keep accurate records.

[1] Advanced technical and operational training is available in this U.S. Navy rating during later stages of an AD's career development.