Five ships of the Royal Navy have borne the name HMS Cynthia. A sixth was planned but never completed:
HMS Cynthia was an 18-gun sloop launched in 1796 and broken up in 1809.
HMS Cynthia was a 16-gun sloop listed between 1810 and 1815.
HMS Cynthia was a 6-gun packet brig purchased in 1826 and wrecked off Barbados on 6 June 1827.
HMS Cynthia was to have been a Rosario-class wooden screw sloop. She was laid down in 1861 but cancelled in 1863.
HMS Cynthia was a destroyer launched in 1898, classified as a D-class destroyer in 1913 and sold in 1920.
HMS Cynthia was a Catherine-class minesweeper launched in 1943 and transferred to the Royal Navy under lend-lease. She was returned to the US Navy in 1947.
