The United States Merchant Marine is an organization composed of United States civilian mariners and U.S. civilian and federally owned merchant vessels. Both the civilian mariners and the merchant vessels are managed by a combination of the government and private sectors, and engage in commerce or transportation of goods and services in and out of the navigable waters of the United States. The Merchant Marine primarily transports domestic and international cargo and passengers during peacetime, and operate and maintain deep-sea merchant ships, tugboats, towboats, ferries, dredges, excursion vessels, charter boats and other waterborne craft on the oceans, the Great Lakes, rivers, canals, harbors, and other waterways. In times of war, the Merchant Marine can be an auxiliary to the United States Navy, and can be called upon to deliver military personnel and materiel for the military.

An able seaman (AB) is a seaman and member of the deck department of a merchant ship with more than two years' experience at sea and considered "well acquainted with his duty". An AB may work as a watchstander, a day worker, or a combination of these roles. Once a sufficient amount of sea time is acquired, then the AB can apply to take a series of courses/examinations to become certified as an officer.