The demi-cannon was a medium-sized cannon, similar to but slightly larger than a culverin and smaller than a regular 42 pounds (19 kg) cannon, developed in the early 17th century.^[2] 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 tiers of 18th century English warships were usually equipped with demi-cannons.

Ships featuring demi-cannons included HMS Sovereign of the Seas,^[1] HMS Resolution^[3] and HMS James, which fought in the Anglo-Dutch naval wars. Demi-cannons were also used on HMS Stirling Castle, the wreck of which was discovered in the Goodwin Sands. Several examples of this weapon were recovered from the site.^[4]

The barrels of demi-cannon were typically 11 feet (3.4 m) long, had a calibre of 6 inches (150 mm) and could weigh up to 5,600 pounds (2,500 kg). It required 18 pounds (8.2 kg) of black powder to fire a 32 pounds (15 kg) round shot. The demi-cannon had an effective range of 1,600 feet (490 m).^[2]

These 32-pounders were used during the 18th century on first-rate ships of the line which carried up to 100 guns. Though powerful, the naval demi-cannons were inaccurate, except at close range, which allowed warships to cause as much damage as possible. Sometimes a single broadside was enough to cripple the enemy vessel.^[5]