The 24-pounder long gun was a heavy calibre piece of artillery mounted on warships of the Age of Sail.

24-pounders were in service in the navies of France, Spain, Great Britain, the Netherlands, Sweden, and the United States.

They were comparable to the Canon de 24 Gribeauval used by the French Army as its largest piece of siege artillery.

From the late 18th 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 guns 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 re-equipped 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 frigate exemplified by the Romaine class.

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,[2] resulting in a two-decker with enough firepower to challenge a three-decker of the time.

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.

It had a muzzle similar to a carronade, and the breeching ring was discarded in favor of a hole in the center of the neck of the cascabel.