Noun
swivel gun (plural swivel guns)
A small cannon attached to a swivel or pivot. It was usually located on a ship's rail so it could have a large range of fire, and could fire anything ranging from small round balls of lead to cannon balls.
The shipyard bubble now blocks pistol bullets, swivel gun shells, and cannon shells. Source: Internet
The sloop’s captain, Jonathan Barnett, ordered the pirates to surrender, but Rackam began firing his swivel gun. Source: Internet