Navy (although the French term also covered ships up to 24 guns, which were classed as post ships within the sixth rate of the British Navy). The name corvette was subsequently also applied to British vessels, but not until the 1830s. American usage, while similar to British terminology into the beginning of the 19th century, gradually diverged. By about 1825 the United States Navy used "sloop-of-war" to designate a flush-deck ship-rigged warship with all armament on the gun deck; these could be rated as high as 26 guns and thus overlapped "third-class frigates," the equivalent of British post-ships. The Americans also occasionally used the French term corvette. History In the Royal Navy, the sloop evolved into an unrated vessel with a single gun deck and three masts, two square rigged and the aft-most fore-and-aft rigged (corvettes had three masts, all of which were square-rigged). Steam sloops had a transverse division of their lateral coal bunkers in order that the lower division could be emptied first, to maintain a level of protection afforded by the coal in the upper bunker division along the waterline. During the War of 1812 sloops of war in the service of the United States Navy performed well against their Royal Navy equivalents. The American ships had the advantage of being ship-rigged rather than brig-rigged, a distinction that increased their manoeuvrability. They were also larger and better armed. Cruizer-class brig-sloops in particular were vulnerable in one-on-one engagements with American sloops-of-war. Decline In the second half of the 19th century, successive generations of naval guns became larger and with the advent of steam-powered sloops, both paddle and screw, by the 1880s even the most powerful warships had fewer than a dozen large calibre guns, and were therefore technically sloops. Since the rating system was no longer a reliable indicator of a ship's combat power, it was abolished together and with it the classifications of sloops, corvettes and frigates. Instead a classification based on the intended role of the ship became common, such as cruiser and battleship. Revival During the First World War, the sloop rating was revived by the British Royal Navy for small warships not intended for fleet deployments. Examples include the Flower classes of "convoy sloops", those designed for convoy escort, and the of "minesweeping sloops", those intended for minesweeping duty. The Royal Navy continued to build vessels rated as sloops during the interwar years. These