This is a list of corvette and sloop classes of the Royal Navy. The original term for ships of fewer than 28 (carriage) guns, but at least 20 guns, was "post ship"; the term 'corvette' was not introduced into the Royal Navy until the 1830s (when the French term was copied), and at that time its use replaced both the larger sloops and also what had previously been categorised officially as 'post ships', i.e. ships of 20, 22 or 24 guns (vessels of 28 guns and above were classed as 'frigates' until 1817, thereafter ships of up to 32 guns were also counted as sixth rates) which were so-called because they were the lowest grade of warship which could be commanded by a 'post captain'; as such, they formed the lower portion of the sixth rate.