24 - pounder long gun The 24 - pounder long gun was a heavy calibre piece of artillery mounted on French warships of the Age of sail , second only to the 36 - pounder long gun . They were comparable to the Canon de 24 Gribeauval used by the Army as its largest piece of siege artillery . 24 - pounders were used as main guns on the heaviest frigates of the early 19th century and on fourth - rate ships of the line , on the second deck of first - rate ships of the line , and on the second deck of a few large third - rate s . Usage . As the 24 - pounder calibre was consistent with both the French and the British calibre systems , it was a widespread gun amongst nations between the 17th and the 19th century . From the late 19th Century , the French Navy used the 24 - pounder in two capacities : as main gun on frigates and 64 - guns , or as secondary artillery on three - deckers and even enlarged versions two - deckers . Under Louis XV , a typical heavy frigate would carry 12 - pounder long gun s until 1772 , when the two vessels of the " Pourvoyeuse " class were built to carry 24 - pounders ; these proved too heavy in practical use , however , and the vessels were reequiped with 18 - pounders , heralding the coming of the 18 - pounder frigate that would become the standard in many navies of the late 18th century . The experiment was tried again in 1785 with " Pomone " , a successful design that opened the way to a standardisation on the 24 - pounder figrate exemplified by the " Romaine " class . Overall , 14 of these heavy frigates were build between " Pomone " in 1785 , and " Poursuivante " in 1798 , each carrying between 24 and 30 24 - pounders . After the Bourbon restauration , frigates were built using a different artillery system , carrying 30 - pounders . Two - deckers used the 24 - pounder in two capacities : on the smallest two - deckers of 64 guns , the 24 - pounder constituted the main artillery , with 26 pieces . Typical 74 - gun vessels carried a 36 - pounder main battery and an 18 - pounder secondary battery , until the enlarged variant of the " Téméraire " class appeared in 1803 , comprising " Vétéran " and " Cassard " . More significantly , the 24 - pounder armed the secondary battery of all 80 - gun ships of the line from 1749 , when the " Soleil - Royal " introduced the practice , resulting in a two - decked with enough firepower to challenge a three - decker of the time . During the reign of Louis XIV , three - deckers were standardised on a 36 - pounder main artillery and an 18 - pounder secondary battery . From the mid - 18th century , under Louis XV , the secondary battery was strengthened to 24 - pounders , beginning with the " Sans - Pareil " design that yielded " Royal Louis " . The other capital ships of the era , " Ville de Paris " , flagship of François Joseph Paul de Grasse during the American War of Independence , and " Bretagne " , flagship at the Battle of Ushant , similarly carried 24 - pounders as secondary batteries . The practices was continued with the " Océan " class and the " Commerce de Paris " class . In the Royal Navy , the 24 - pounder was similarly used on some heavy frigates , which carried 26 guns . Fourth - rate ships carried 22 on their secondary batteries , and third - rate s carried 32 . First - rate s carried thirty - four 24 - pounders on their middle deck .