A corvette (sometimes corvet) is a small, maneuverable, lightly armed warship, originally smaller than a frigate (2,000+ tons) and larger than a coastal patrol craft or fast attack craft (500 tons or less), although many recent designs are approaching the size of smaller frigates (3,000 tons). During the Age of Sail, corvettes were smaller than frigates and larger than sloops-of-war, usually with a single gun deck. Although almost all modern navies use ships smaller than frigates for coastal duty, not all of them use the term corvette (via Middle French, from a Dutch word corf, a type of boat) or equivalent. The rank "corvette captain", equivalent in many navies to "lieutenant commander", derives from the name of this type of ship.