A Boatswains Mate (BM) is a rating in the United States Navy and Coast Guard). They are responsible for a wide range of duties related to navigation and seamanship, and are considered the heart of every ship. The rating of Boatswains Mate dates back to the American Revolutionary War and is one of the oldest U.S. Navy ratings in continuous existence).

The duties of a Boatswains Mate can vary depending on the capacity and mission of the vessel or shore installation to which they are assigned). They can act as landing signalmen enlisted (LSE), guiding helicopters to the designated flight deck of a ship, or as lookouts of Navy ships, searching the sea for enemy vessels and hazards to navigation). When operating a boat as coxswain, they are in charge of executing the mission and responsible for the safety of their crew members. They are also capable of performing almost any task in connection with deck maintenance, small boat operations, and more.

A boatswain, also known as a bosun, is the most senior rate of the deck department and is responsible for the components of a ships hull. The boatswain supervises the other members of the ships deck department and typically is not a watchstander, except on vessels with small crews.