Until the nineteenth century Royal Navy officers who were captains by rank and in command of a naval vessel were referred to as post-captains.

Captain (D) or Captain Destroyers, afloat, was an operational appointment commanding a destroyer flotilla or squadron, and there was a corresponding administrative appointment ashore,[1] until at least a decade after the Second World War.

The title was probably used informally until the abolition of frigate and destroyer squadrons with the Fleet FIRST reorganisation circa 2001.

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.