Fifth - rate In Britain ' s Royal Navy during the classic age of fighting sail , a fifth rate was the penultimate class of warships in a hierarchal system of six " ratings " based on size and firepower . Rating . The rating system in the British ( originally English ) Royal Navy as originally devised had just four rates , but early in the reign of Charles I the original fourth rate ( derived from the " Small Ships " category under his father , James I ) was divided into new classifications of fourth , fifth , and sixth rates . While a fourth rate was defined as a ship of the line , fifth and the smaller sixth rates were never included among ships - of - the - line . Nevertheless , during the Anglo - Dutch Wars of the 17th century , fifth rates often found themselves involved among the battle fleet in major actions . Structurally , these were two - deckers with a complete battery on the lower deck , and fewer guns on the upper deck ( below the forecastle and quarter decks , usually with no guns in the waist on this deck ) . The fifth rates at the start of the 18th century were small two - decker s , generally either 40 - gun ships with a full battery on two decks , or " demi - batterie " ships , carrying a few heavy guns on their lower deck ( which often used the rest of the lower deck for row ports ) and a full battery of lesser guns on the upper deck . However , the latter were gradually phased out , as the low freeboard ( the height of the lower deck gunport sills above the waterline ) meant that it was often impossible to open the lower deck gunports in rough weather . The 40 - gun ( or later 44 - gun ) fifth rates continued to be built until the latter half of the 18th century ( a large group were built during the American War of Independence ) . From mid - century , a new fifth - rate type was introduced : the classic frigate , with no gun ports on the lower deck , and the main battery of from 26 to 30 guns disposed solely on the upper deck , although smaller guns were mounted on the quarterdeck and forecastle . Fifth - rate ships served as fast scouts or independent cruiser s and included a variety of gun arrangements . The fifth rates of the 1750s generally carried a main battery of twenty - six 12 - pounders on the upper deck , with six 6 - pounders on the quarterdeck and forecastle ( a few carried extra 6 - pounders on the quarterdeck ) to give a total rating of 32 - guns . Larger fifth rates introduced during the late 1770s carried a main battery of twenty - six or twenty - eight 18 - pounders , also with smaller guns ( 6 - pounders or 9 - pounders ) on the quarterdeck and forecastle . Tonnage ranged from 700 to 1450 tons , with crews of 215 to 294 men . To be posted aboard a fifth - rate ship was considered an attractive assignment . Fifth rates were often assigned to interdict enemy shipping , offering the prospect of prize money for the crew . Fifth - rate frigates were considered useful for their combination of maneuverability and firepower , which , in theory , would allow them to outmaneuver an enemy of greater force and run down one of lesser force . It was for this reason that frigates of this sort were commonly used in patrol and to disrupt enemy shipping lanes much as heavy cruisers would later in history .