Military members performing duty at sea are entitled to a special monthly pay, known as "Career Sea Pay."
Military Sea Pay hasn't changed in several years. It last changed for Navy and Marine Corps personnel in 2001, Army soldiers in 2002, and Air Force folks in 1988.
Sea duty, for the purpose of entitlement to career sea pay, is service performed by a member under orders issued by competent authority:
(1) While permanently assigned for duty to a ship, ship-based staff, or ship-based aviation unit and serving in a ship whose primary mission is accomplished underway. If the member is temporarily assigned to duties ashore, sea duty continues for the first 30 consecutive days from the beginning of the temporary duty. In other words, if a member is permanently assigned to a ship, but performs duty ashore for 60 days, the first 30 of those days would still count as sea duty, for the purposes of receiving sea duty pay.
(2) While temporarily assigned for duty to a vessel, ship-based staff, or ship-based aviation unit and serving on a ship whose primary mission is accomplished underway.
(3) While permanently or temporarily assigned for duty to a vessel or ship-based staff and serving on a ship with a primary mission accomplished in port, but only during that period while the ship is away from its home port. A ship is considered away from its home port whenever it is at sea, or in a port located more than 50 miles away from the home port.
(4) While serving as a member of the off crew of a two-crewed submarine.
Here are the Career Sea Pay rates for 2011: