Captain (Capt) is a senior officer rank of the Royal Navy. It ranks above Commander and below Commodore and has a NATO ranking code of OF-5. The rank is equivalent to a Colonel in the British Army and Royal Marines, and to a Group Captain in the Royal Air Force. There are similarly named equivalent ranks in the navies of many other countries.
In the Royal Navy, the officer in command of any warship of the rank of Commander and below is informally referred to as "the Captain" on board, even though holding a junior rank, but formally is titled "the Commanding Officer" (or CO). In former times Royal Navy officers who were Captains by rank and in command of a naval vessel were referred to as Post-Captains; this practice is now defunct.
Ashore, the rank of Captain is often verbally described as "Captain RN" to distinguish it from the more junior Army and Royal Marines rank, and in naval contexts, as a "Four Ring Captain" (referring to the uniform lace) to avoid confusion with the title of a seagoing Commanding Officer. In the Ministry of Defence, and in Joint Service establishments, a Captain may be referred to as a "DACOS" (standing for Deputy Assistant Chief of Staff) or an "AH" (Assistant Head), from the usual job title of OF5-ranked individuals who work with civil servants.
Insignia and uniform
The rank insignia features four rings of gold braid with a loop in the upper ring.
When in mess dress or mess undress, officers of the rank of Captain and above wear gold-laced trousers (the trousers are known as "tin trousers", and the gold lace stripes thereon are nicknamed "lightning conductors"), and may wear the undress tailcoat (without epaulettes).