Quartermaster is one of two different military occupations.
In land armies, especially US units, a quartermaster is either an individual soldier or a unit who specializes in distributing supplies and provisions to troops. The senior unit, post or base supply officer is customarily referred to as "the quartermaster". Often the quartermaster serves as the S-4 in US Army, US Marine Corps units and NATO units.
In many navies, quartermaster is a non-commissioned officer (petty officer) rank for personnel responsible for their ship's navigation. In the US Navy, the quartermaster is responsible for the ship's navigation and maintenance of nautical charts and maps. Aboard merchant ships, quartermasters are usually the Able Seamen assigned to bridge watches. A naval quartermaster's main task is to steer the ship and apply the helm orders given by the Captain or watch officers.
Read more about Quartermaster: Land Armies, Pirate Quartermasters, Scouting