rating and the actual number of cannons any individual vessel might carry. One therefore needs to distinguish between the established armament of a vessel (which rarely altered) and the actual guns carried, which might happen quite frequently for a variety of reasons; guns might be lost overboard during a storm, or "burst" in service and thus useless, or jettisoned to speed the ship during a chase, or indeed removed down into the hold in order to use the ship (temporarily) as a troop transport, or for a small vessel, such as the schooner , to lower the centre of gravity and thus improve stability in bad weather. Also some of the guns were removed from a ship during peacetime service, to reduce the stress on the ship's structure, which is why there was actually a distinction between the wartime complement of guns (and men) and the lower peacetime complement—the figure normally quoted for any vessel is the highest (wartime) establishment. Royal Navy rating system in force during the Napoleonic Wars Notes The smaller fourth-rates, primarily the 50-gun ships, were, from 1756 on, no longer classified as ships of the line. Since not big enough to stand in the line of battle, were often called frigates, though not classed as frigates by the Royal Navy. They were generally classified, like all smaller warships used primarily in the role of escort and patrol, as "cruisers", a term that covered everything from the smaller two-deckers down to the small gun-brigs and cutters. The larger fifth-rates were generally two-decked ships of 40 or 44 guns, and thus not "frigates", although the 40-gun frigates built during the Napoleonic War also fell into this category. The smaller sixth-rates were often popularly called frigates, though not classed as "frigates" by the Admiralty officially. Only the larger sixth-rates (those mounting 28 carriage guns or more) were technically frigates. The ton in this instance is the burthen tonnage (bm). From c.1650 the burthen of a vessel was calculated using the formula , where was the length, in feet, from the stem to the sternpost, and the maximum breadth of the vessel. It was a rough measurement of cargo-carrying capacity by volume, not displacement. Therefore, one should not change a measurement in "tons burthen" into a displacement in "tons" or "tonnes". 1817 changes In February 1817 the rating system changed. The recommendation from the Board of Admiralty to the Prince