Medusa was laid down as HDML 1387 at the yard of R A Newman and Sons in Poole, Dorset, on 27th July 1943, and launched on 20th October 1943. She was powered by two Gardner 8L3 diesel engines and was equipped with a Gardner 1L2 auxiliary. Her armament was a 2 pounder and a 20mm Oerlikon, with two twin Vickers 'K' machine guns, and six depth charges.
Under the command of Temporary sub-lieutenant Maurice Liddiard, RNVR, who commanded her throughout her war service, she was initially involved in convoy escort work in the Western Approaches. In the spring of 1944 she joined the 149th HDML Flotilla, was based at Portland, and took part in Exercise Fabius 1, which was a practice assault carried out by the Americans at Slapton Sands in Devon. Medusa took part in the 'D'-Day landings, arriving off Omaha Beach on the night before the invasion and remaining on station for 30 hours as the Navigational Leader for approach channel 4.
In October 1944, Medusa was transferred to the 185 Auxiliary Minesweeping Flotilla, based on the Medway.
Early in 1945, Medusa crossed to Ostend and from there took passage to IJmuiden where she accepted the surrender of the occupying German forces. From IJmuiden she navigated the North Sea Canal to Amsterdam, the first allied ship to do so.
Post war, Medusa was redesignated Fast Despatch Boat (FDB) 76 and was allocated to Cardiff University, and then Bristol, as a training vessel. In 1949 she was allocated to London Division RNVR and temporarily assumed the name HMS Thames. Whilst in London she was redesignated Seaward Defence Motor Launch (SDML) 3516. In 1953 she became an Hydrographic Survey Vessel with the pennant number A 323, and was finally named HMS Medusa in 1961.
In 1968, after 25 years' service, she was sold by the Admiralty in a condition they considered fit only for the breakers. She was purchased by a group from Weymouth and then, over a period of 18 years, was painstakingly restored to a seagoing condition once again, such that her life was extended to more than 60 years. The Medusa Trust was formed in 2002 to take ownership of the vessel, and raise funds for a major restoration programme. At the same time the Medusa Support Group was formed and now provides volunteers for maintenance, crew for the vessel when she goes to sea as well as guides to show visitors around the vessel in port.
Medusa is in the national historic fleet and is the first vessel to fly the fleet red ensign.
A booklet covering the design and construction of Medusa and her history is available from the Trust.