The 12-pounder long gun was an intermediary calibre piece of artillery mounted on warships of the Age of Sail.

From the late 18th 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.

The capture of Hermione in 1757 encouraged the British to imitate her design, yielding the Southampton 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-rates.

24 guns from the reigns of Queen Anne and King George I survive at Fort Prince of Wales in Hudson bay.

The mensuration of 1743 gives the weight of the 9 ft 12-pounder gun as 32 hundredweight 2 quarter 3 pounds, and the dimensions there are almost identical with those in Adye's notebook of 1766.

At the same time, the gun of 9 ft 34 3/4 hundredweight was recommended for sometimes replacing the 18-pounder in batteries where quick fire was required against storming parties or boat attacks.