A naval Quartermaster is responsible for the watch-to-watch navigation of the ship, under the direction of the navigator. Maintenance, correction, and preparation of nautical charts and navigation publications, responsibility for navigational instruments and clocks, and training of ship's lookouts and helmsmen are among the Quartermaster's duties.

The Quartermaster rate (along with Gunner's Mate, Cook [Mess Management Specialist], and Boatswain's Mate) is one of the four "right-arm" rates: the oldest rates in the Navy. Quartermasters in the days of sail were responsible for monitoring the helmsman--not only were the wooden ships subject to wave action, but flaws in the wind could take the ship aback. They also assisted in various navigational duties (heaving the log, shooting azimuths, etc.). Their domain was the quarterdeck, where the ship's wheel was located, hence the name. The rate dates back beyond the American Navy to the English Navy. Other possibly confusing terms: the ship's Master was the warrant officer charged with the ship's navigation--the Navigator in modern terminology (and a commissioned officer). The Master's Mates were warrant officers somewhat on a par with senior midshipmen.

The primary watch a modern Quartermaster stands is Quartermaster of the Watch (QMOW): the watch-to-watch representative of the Navigator, and whose primary responsibility is safe navigation of the ship. He plots the ship's position on the chart, maintains a dead reckoning plot of the ship's projected position, obtains, or assists in obtaining fixes, by shooting the sun, moon, or star positions and elevation or by electronic or satellite navigational devices, plots fixes and advises the Officer off the Deck (OOD) on navigational status. He also maintains the ship's Deck Log, a chronological detailing of all pertinent events.

(The following is adapted from the Quartermaster 1 & C Rate Training Manual) The Quartermaster is a general rating. The duties of a Quartermaster deal with supervision of personnel, maintenance of all spaces assigned to the navigation department, standing watch as quartermaster of the watch (QMOW), keeping charts up-to-date, mastery of operational techniques of electronic aids to navigation, use of navigational instruments (such as the sextant, alidades, parallel rulers, and dividers), use of navigation tables, and security of classified material.

Quartermaster is one of the few ratings for which billets exist in virtually all types of Navy ships, from the largest to the smallest--both surface craft and submarines. The nature of the First Class or Chief Quartermaster's work depends mainly on the type of ship to which he is assigned. Aboard carriers, cruisers, and other deep draft ships, the Quartermaster force is likely to be quite large; the senior Quartermaster spends much of his time on administrative duties and supervision. Aboard meduim size ships, the senior Quartermaster frequently is the assistant to the navigator, and most of his time is taken up in actual navigational duties. Aboard very small ships, the senior Quartermaster usually is the navigator's assistant, and may have the additional responsibility of supervising the ship's signal force. At the first class and chief level, Quartermasters may also be assigned to sea duty as petty officer in charge of tugboats or other types of yard craft.