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 sixth-rate ship (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.

Sea officers often referred to the post ships as frigates though technically the Admiralty scrupulously never described them as such.

The vessels were frigate-built, with traditional quarterdecks and forecastles (the defining characteristic of post ships, distinguishing them from 20-gun ship-sloops), but, unlike true frigates, they lacked an orlop platform amidships.

In peacetime the Royal Navy frequently used them as substitutes for frigates, especially in distant foreign stations.

The United States Navy termed ships of this type "third-class frigates."