The Ordnance QF Hotchkiss 6 pounder gun were introduced to defend against watercraft capable of independent operation underwater usually referred to as "boats" rather than what?
QF 6-pounder Hotchkiss The Ordnance QF Hotchkiss 6 pounder gun Mk I and Mk II or QF 6 pounder 8 cwt were a family of long-lived light 57 mm naval guns introduced in 1885 to defend against new, small and fast vessels such as torpedo boats and later submarines. There were many variants produced, often under license which ranged in length from 40 to 58 calibers, but 40 caliber was the most common version.
Post ship Post ship was a designation used in the Royal Navy during the second half of the 18th century and the Napoleonic Wars to describe a ship of the sixth rate (see rating system of the Royal Navy) that was smaller than a frigate (in practice, carrying fewer than 28 guns), but by virtue of being a rated ship (with at least 20 guns), had to have as its captain a post captain rather than a lieutenant or commander. Thus ships with 20 to 26 guns were post ships, though this situation changed after 1817.