Of the four U.S. military service branches, the U.S. Navy has a rank structure that differs the most from the others. While an Army captain holds the paygrade of O-3, a Navy captain is a much more senior officer, at pay grade O-6. A Navy captain is also just one step below the four admiral flag officer ranks. Because they're senior officers and have so many responsibilities, Navy captains also earn pay that compensates them for the jobs they perform.

Line and Staff

Like its sister services, the Navy has both line and staff officers. Navy line officers are the people commanding ships, submarines, aircraft squadrons and many Navy shore installations. Navy staff corps officers include doctors and lawyers, and they may rise to command Navy installations pertinent to their specialties, such as Navy hospitals. Staff corps officers, though, can't command ships and other line units. Though actual Navy captains hold paygrade O-6, lower-ranking officers commanding their own units may also be called "captain" or "skipper."

Navy Captain Pay

As of 2013, a Navy captain in paygrade O-6 earns basic pay ranging from $6,605 to $10,737 monthly. Like all U. S. military officers, a Navy captain's pay is based on rank and years of service. A Navy captain of 18 years service earns $9,090 monthly while one with 22 years service earns $9,781. Within the Navy's line community, it can also take an average of 21 to 23 years for an officer to advance from Ensign O-1 to Captain O-6.

Navy Special Pay

Navy captains and below can earn special pay, either for the jobs they perform or for their positions as commanding officers. This includes flight pay, sea pay and hazardous-duty pay. Navy officers at paygrade O-6 and below also earn additional pay if they're assigned as commanding officers of designated units such as ships. A Navy captain O-6 commanding an aircraft carrier, for instance, would be entitled to what's called "command responsibility pay."

Captain Promotion Opportunity

The Navy's non-warrant-officer commissioned-officer ranks run from O-1 ensign to O-10 admiral. Additionally, promotion to higher Navy commissioned officer ranks becomes progressively more difficult as officers move up the ladder. By law, the number of Navy O-4 lieutenant commanders, O-5 commanders and O-6 captains is strictly controlled, meaning competition for promotion becomes extremely keen. Navy officers twice failing selection for promotion to the next higher paygrade, such as commanders "failing to select" to captain, are generally either discharged or retired from service.