The U.S. Navy occupational rating of boatswain's mate is a designation given by the Bureau of Naval Personnel to enlisted members, who were rated or "striking" for the rating, as a deck seaman. The informal reference/address for a boatswain's mate is "Boats".
The "Boats" form the core of a Navy ship's manpower ... keeping the ship in shape from top to bottom ... performing many of the crucial tasks to put and keep a ship underway.
A Boatswain's mate advances in rate ... as he/she becomes more specialized.
U.S. Department of Defense video by U.S. Air Force Tech. Sgt. Jared Whitecar - July 2019