Captain (Naval)

Common military ranks in English
Navies	Armies	Air forces
Commissioned and Non-commissioned officers
Admiral of the fleet	Marshal or Field marshal	Marshal of the air force
Admiral	General	Air chief marshal
Vice admiral	Lieutenant general	Air marshal
Rear admiral	Major general	Air vice-marshal
Commodore	Brigadier or Brigadier general	Air commodore
Captain	Colonel	Group captain
Commander	Lieutenant colonel	Wing commander
Lieutenant commander	Major or Commandant	Squadron leader
Lieutenant	Captain	Flight lieutenant
Sub-lieutenant	Lieutenant or First lieutenant	Flying officer
Ensign	Second lieutenant	Pilot officer
Midshipman	Officer cadet	Flight cadet
Enlisted grades
Warrant officer or Chief petty officer	Warrant officer or Sergeant major	Warrant officer
Petty officer	Sergeant	Sergeant
Leading seaman	Corporal	Corporal
Seaman	Private	Aircraftman

Captain is the name most often given in English-speaking navies to the rank corresponding to command of the largest ships. The rank is equal to the army rank of colonel.

Equivalent ranks worldwide include "ship-of-the-line captain" (e.g. France, Argentina, Spain), "captain of sea and war" (e.g. Portugal), "captain at sea" (e.g. Germany, Netherlands) and "captain of the first rank" (Russia).

The NATO rank code is OF-5, although the United States of America uses the code O-6 for the equivalent rank (as they do for all OF-5 ranks).

Any naval officer who commands a ship is addressed by naval custom as "captain" while aboard in command, regardless of his or her actual rank, even though technically an officer of below the rank of captain is more correctly titled the commanding officer, or C.O. Officers with the rank of captain travelling aboard a vessel they do not command should be addressed by their rank and name (e.g., "Captain Smith"), but they should not be referred to as "the captain" to avoid confusion with the vessel's captain. The naval rank should not be confused with the army, air force, or marine ranks of captain, which all have the NATO code of OF-2.

On large US ships (e.g., aircraft carriers), the executive officer (XO) may be a captain in rank, in which case it would be proper to address him by rank. Often the XO prefers to be called "XO" to avoid confusion with the CO, who is also a captain in rank and the captain of the ship. The same applies to aircraft carriers in the U.S. Navy, where the commander and deputy commander of the embarked carrier air wing are both captains in rank, but are addressed by the titles of "CAG" and "DCAG", respectively.

Captains with sea commands generally command ships of cruiser size or larger; the more senior the officer, the larger the ship, but ship commanders do not normally hold a higher rank than captain. In the Royal Navy, a captain might command an aircraft carrier, an amphibious assault ship, or the Ice Patrol Ship, while naval aviator and naval flight officer captains in the U.S. Navy command aircraft carriers, large-deck amphibious assault ships, carrier air wings, maritime patrol air wings, and functional and specialized air wings and air groups.

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Wikipedia