12 - pounder long gun The 12 - 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 18th century , on the second deck of fourth - rate ships of the line , and on the upper decks or castles of 80 - gun and 120 - gun ships of the line . Naval 12 - pounders were similar to 12 - pound Army guns in the Gribeauval system : the canon lourd de 12 Gribeauval , used as a siege weapon , and the canon de 12 Gribeauval , which was considered a heavy field artillery piece . Usage . As the 12 - 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 12 - pounder in three capacities : as main gun on early frigates under Louis XIV , on standard frigates under Louis XV and on light frigates under Louis XVI ; as secondary artillery on 64 - gun ships ; to arm the castles of 80 - gun ships of the line ; and to equip the third deck of early first - rate ships . Under Louis XIV , frigates were organised into " first - rank frigates " , which were small two - deckers comparable in role to the 60 - gun ships of the 19th century , and smaller " second - rank " frigates . The first - rank frigates carried the 12 - pounder as main artillery on their lower deck . Later , under Louis XV , the frigate took its modern shape with a single artillery deck complemented by smaller pieces on the castles ; new heavy frigates were developed to carry 26 12 - pounders , with " Hermione " as lead ship of the series . " Hermione " was captured by the British in 1757 and was swiftly imitated . Breakthrough towards fielding heavier guns were made in 1772 , when the two units of the " Pourvoyeuse " class were built , with 24 - pounders intended , but 18 - pounders used in practice , and the 12 - pounder remained the standard issue on most units . Under Louis XVI , the heavier 18 - pounder frigate became predominant , with over 130 units produced , but the French Navy still had around 70 lighter 12 - pounder frigates in commission . On 64 - gun two - deckers , the 12 - gun was used as secondary artillery , to supplement the 24 - pounder main batteries . 28 guns were carried on the top gun - deck . Larger units used the 12 - pounder to complement the firepower provided by their main and secondary artillery . On 80 - gun ships of the " Tonnant " class and " Bucentaure " class , they armed the forecastle and the poop deck . On capital ships , the 12 - pounder was used on the third deck from the reign of Louis XIV , with units like " Royal Louis " or " Soleil - Royal " as typical examples . While the secondary artillery of these 100 - gun ships evolved from 18 - pounders s to 24 - pounders s , the 12 - pounder remained the standard gun on the third deck until 1803 , when the " Océan " class ship " Impérial " became the first 120 - gun to carry 18 - pounders on her third battery . In the Royal Navy , the 12 - pounder was used in a similar capacity . The capture of " Hermione " in 1757 encouraged the British to imitate her design , yielding the " Southampton " class and " Richmond " class frigates . The 12 - pounder also equipped the castles on razeed ships , where 12 pieces were mounted , and the 22 - gun secondary battery of 50 - gun fourth - rate s . Finally , 30 were installed on the third deck of 90 - gun second - rate s .