During the 18th and 19th centuries, a sloop-of-war was a warship of the Royal Navy with a single gun deck that carried up to 18 guns. 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. In technical terms, even the more specialised bomb vessels and fire ships were classed by the Royal Navy as sloops-of-war, and in practice these were employed in the role of a sloop-of-war when not carrying out their specialised functions.