HMS Myrmidon was a 20-gun Hermes-class sixth-rate post ship built for the Royal Navy during the 1810s.

Myrmidon was armed with eighteen 32-pounder carronades and a pair of 9-pounder cannon as chase guns.

[1] Myrmidon, the second ship of her name to serve in the Royal Navy,[2] was ordered on 2 August 1811, laid down in July 1812 in Milford Dockyard, Wales, and launched on 18 June 1813.

[1] The ship's first commission began in August 1813 under the command of Captain Valentine Gardner while she was still fitting out.

The ship was reclassified in February 1817 as a 20-gun sloop and was in the Mediterranean that year before paying off on 19 November 1818.