Captain ( naval ) Captain is the name most often given in English - speaking navies to the rank corresponding to command of the largest ships . The NATO rank code is OF - 5 , equivalent to an army full colonel . The equivalent rank in many navies is Ship - of - the - Line Captain . Other equivalent ranks in other navies notably include Captain of Sea and War or Captain at Sea . Role . The command of a ship is most often given to the naval rank equivalent to a commissioned officer between commander ( OF - 4 ) and commodore or rear admiral ( OF - 6 ) . The Polish Navy is , however , a notable exception " naval captain " in position of Lieutenant or Captain Lieutenant and OF - 5 rank being a " commander " ( " komandor " ) . The naval rank should not be confused with the army , air force or marine rank of captain , which has a NATO code of OF - 3 . Title . Any naval officer who commands a ship ( titled Commanding Officer , or CO ) is addressed as " captain " while aboard in command , by naval custom . 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 . On large ships ( e . g . , carriers ) , the XO ( Executive Officer ) may be a captain in rank , in which case it would be proper to address the XO by rank . Often the XO prefers to be called XO to avoid confusion with the CO ( Commanding Officer ) , who is also a captain in rank and the captain of the ship . In some navies , captains by rank are addressed as Commodore to avoid confusion with the ship ' s commander . Throughout the Middle Ages the navy was an " ad - hoc " group of ships contracted for the duration of a given conflict and disbanded thereafter . The ship ' s " master " , who would command the ship during peacetime , would also remain in control of all things nautical during wartime . The " captain " was merely the commander of the embarked infantry contingent upon the ship who , with the help of his " lieutenants " , would act as the agent of the king — and hence " de facto " commander — while the ship was contracted with the Navy . During Tudor times , the title of " captain " began to refer to the commander of a ship of the Royal Navy , once that organization became established and maintained a standing fleet . Commands . 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 a destroyer flotilla with the appointment ( not rank ) of Captain ( D ) ( or Captain ( Destroyers ) ) , while Naval Aviator and Naval Flight Officer Captains in the U . S . Navy command aircraft carrier s , large - deck amphibious assault ships , carrier air wings , maritime patrol air wings and functional and specialized air wings and air groups . The more senior the officer , the larger the ship , but ship commanders do not normally hold a higher rank than captain . Rear Admirals will normally embark on large capital ships such as aircraft carriers , which will function as the flagship for their strike group or battle group , but a captain will retain command of the actual ship . Even when a senior officer who is in the ship ' s captain ' s chain of command is present , all orders are given through the captain as a courtesy . Many captains hold shore commands and staff positions afloat and ashore . Captains in national navies . The following articles deal with the rank of captain as it is used in various navies .