Hermes-class post ship
The "Hermes" class were a series of four 20-gun ships, launched between 1811 and 1816. Two pairs of ships were produced, to slightly different designs – the first two had 20 guns and were unrated flush-decked ship-sloops, whilst the latter two were converted to 26-gun sixth-rates. The design was based on the ex-French 20-gun corvette , which the British had captured in 1796. The first pair was built at Milford Dockyard on the north side of Milford Haven. was launched in 1811 and in 1813. Milford Dockyard was closed following their  construction, and the second pair were built at the new Pater (later Pembroke Dock) Dockyard on the south side of Milford Haven. The second pair – and – were launched on the same date in 1816. They were modified at Plymouth Dockyard in 1820 and 1821 respectively, before their first commission, by the addition of quarterdecks and forecastle to what had originally been flush-deck vessels, and they were at that time re-classed as 26-gun sixth rate post ships. The "Cyrus" class was based on the design of the "Myrmidon" of the "Hermes" class.