Three ships of the Royal Navy have been named HMS Adamant:
- was a 50-gun fourth rate launched in 1780. She was reduced to harbour service in 1809 and was broken up in 1814.
- was a submarine depot ship launched in 1911, commissioned in 1912 and sold in 1932.
- was a submarine depot ship launched in 1940 and broken up in 1970.
See also
- The sloop was renamed HMS Adamant II in 1930, and was sold later that year.
- is a small submarine tender and personnel ferry in the Royal Maritime Auxiliary Service. She was launched in 1992 and is currently in service.