Six ships of the Royal Navy have borne the name HMS Cossack, after the Cossack people of Eastern Europe, whilst another was begun but was cancelled while building:
HMS Cossack (1806) was a 22-gun sixth-ratepost-ship, begun under the name Pandour in 1805, but renamed before being launched in 1806. She was broken up in 1816.
HMS Cossack was to have been a steam gunvessel, laid down at Portsmouth Dockyard in 1846, but cancelled in May 1849.
HMS Cossack (1854) was ordered as the Russian ship Witjas, a wood screw corvette building on the Thames at Northfleet, but the British government seized her while she was under construction in 1854; she was sold in 1875.