The demi-cannon was a medium sized cannon, similar to but slightly larger than a culverin and smaller than a regular 42lb (19kg) cannon developed in the early 17th century. A full cannon fired a 42-pound shot but these were discontinued in the 18th century as they were seen as too unwieldy . The lower tier of 17th Century English warships were usually equipped with demi-cannons. Ships featuring demi-cannons included HMS Sovereign of the Seas, HMS Resolution and HMS James, which fought in the Anglo-Dutch naval wars.

The barrels of demi-cannon were typically 11ft (3.4m) long, had a calibre of 6 inches (15.4cm) and could weigh up to 5600lb (2540kg). It required 18lb (8kg) of black powder to fire a 32lb (14.5kg) round shot. The demi-cannon had an effective range of 1600ft (490m).
These 32-pounders were used during the 18th century on first-rate three-decker ships of the line which carried up to 100 guns. Though powerful, the naval demi-cannons were inaccurate except at close range so opposing warships would try to get as close as possible before firing their broadside in order to cause as much damage as possible; sometimes a single broadside was enough to cripple the enemy vessel.