Sloop-of-war

The rating system of the Royal Navy covered all vessels with 20 or more guns; thus, the term encompassed all unrated warships, including gun-brigs and cutters.

A sloop-of-war was quite different from a civilian or mercantile sloop, which was a general term for a single-masted vessel rigged in a way that would today be called a gaff cutter (but usually without the square topsails then carried by cutter-rigged vessels), though some sloops of that type did serve in the 18th century British Royal Navy, particularly on the Great Lakes of North America.

The brig rig was economical of manpower – important given Britain's chronic shortfall in trained seamen relative to the demands of the wartime fleet.

The other limitation of brig sloops as opposed to post ships and frigates was their relatively restricted stowage for water and provisions, which made them less suitable for long-range cruising.

The Royal Navy also made extensive use of the Bermuda sloop, both as a cruiser against French privateers, slavers, and smugglers, and also as its standard advice vessels, carrying communications, vital persons and materials, and performing reconnaissance duties for the fleets.

The Royal Navy favoured multi-masted versions, as it was perennially short of sailors at the end of the 18th century, and its personnel received insufficient training (particularly in the Western Atlantic, priority being given to the continuing wars with France for control of Europe).

Since the rating system was no longer a reliable indicator of a ship's combat power, it was abolished altogether and with it the classifications of sloops, corvettes and frigates.

During the First World War, the sloop rating was revived by the British Royal Navy for small warships not intended for fleet deployments.

These sloops were small warships intended for colonial "gunboat diplomacy" deployments, surveying duties, and acting during wartime as convoy escorts.

During World War II, 37 ships of the Black Swan class were built for convoy escort duties.

Built to mercantile standards and with (initially) simple armaments, these vessels, notably the Flower and River classes, were produced in large numbers for the Battle of the Atlantic.