18 - pounder long gun The 18 - pounder long gun was an intermediary calibre piece of artillery mounted on warships of the Age of sail . They were used as main guns on the most typical frigates of the early 19th century , on the second deck of third - rate ships of the line , and even on the third deck of late first - rate ships of the line . Usage . As the 18 - pounder calibre was consistent with both the French and the British calibre systems , it was used in many European navies between the 17th and the 19th century . It was a heavy calibre for early ships of the line , arming , for instance , the main batteries of the " Couronne " in 1636 . From the late 18th Century , the French Navy used the 18 - pounder in three capacities : as the main gun on frigates , as the battery on the upper gundeck of two - deckers , and lastly on the top deck of three - deckers . French frigates began carrying the 18 - pounder under Louis XV , when the two " Pourvoyeuse " class frigates , originally designed to carry 24 - pounders , were equipped with it ; at the time , a typical frigate would carry 12 - pounders . Under Louis XVI , from 1779 , the 18 - pounder gradually became the standard calibre for frigates , starting with the " Hébé " Class . These frigates were build on standard patterns designed by Jacques - Noël Sané , carrying 26 , and later 28 main guns , complemented with smaller pieces on the forecastle . Around 130 of these frigates were built . At the end of the Empire , 24 - pounder frigates began supplanting the 18 - pounder frigates . Frigates built after the Bourbon restauration , used a different artillery system , one involving 30 - pounders . On two - deckers , the 18 - pounder was mounted on the upper deck as secondary artillery , to complement the 36 - pounder main artillery on the lower deck . A 74 - gun would carry thirty 18 - pounders ; this lighter secondary battery added firepower to the ship without raising the centre of gravity too much . In rough weather , vessels often could not use their main battery lest water enter through the gun - port s , and the secondary battery then became the vessel ' s main armament ; for example , the " Droits de l ' Homme " was effectively reduced to the firepower of a frigate when she fought the action of 13 January 1797 in stormy weather , leading to her destruction at the hand of two British frigates that would normally not have been a match for her ; in the opposite case , during the Glorious First of June , the " Vengeur du Peuple " used her main batteries but became unmanageable and sank after taking in water from her lower gun - ports whose covers had been ripped off in a collision with HMS " Brunswick " . Three - deckers used 36 - pounders on their lower decks and 24 - pounders on their second deck . Until 1803 , the third deck was equipped with 12 - pounder guns , as a heavier gun would have destabilised the ship ; after this date , however , Sané introduced design improvements that allowed installation of 18 - pounder on the third deck of " Impérial " ; later 120 - gun ships of the line used the same arrangement ; these ships carried thirty - four 18 - pounders . The Royal Navy used the 18 - pounder on frigates , which carried 28 guns . Fourth rate s ships carried 26 on their secondary batteries , and third rate s carried 28 . Unlike the French , the British used second rate s , of 90 to 98 guns ; the 90 - gun vessels carried thirty 18 - pounders on their middle deck , while the 98 - gun vessels carried a total of sixty 18 - pounders , distributed over both the second and the third deck . First rate s carried thirty - four 18 - pounders on their third deck and 24 - pounders on the middle deck .