portpiece

plural portpieces

1. a smaller cannon or gun mounted on the side of a ship. These were often used for close-range engagements or for firing at smaller targets.

   PORT-PIECE An ancient piece of ordnance used in our early fleets.

   1867, Admiral W. H. Smyth, The Sailor’s Word Book: An Alphabetical Digest of Nautcal Terms Including Some More Especially Military and Scientific but Useful to Seamen as Well as Archaisms of Early Voyagers Etc., page 539

   2 more examples

   They fired 3½ lbs of powder against 3¼ lbs of the portpiece, an iron shot of 2½ lbs or a stone of 2¼.

   1898, Julian S, Corbett, editor, The Spanish War 1585-1587 (Publications of the Navy Records Society), volume XI, Navy Records Society, page 332

   A portpiece was a gun witn an internal barrel diameter of 5½in, and a chamber of 3½in.

   1990, Peter Kirsch, The Galleon: The Great Ships of the Armada Era, Conway Maritime, page 54