Special Purpose Vessel (SSV) is a designation used by the Royal Navy for a diverse group of ships in service; a general term for ships that do not fit into more conventional categories.
The United States Navy List of 1906 listed 19 special purpose vessels, mostly floating craft assigned to shore establishments.
In World War I, this category included yachts (five, including three royal yachts), ferries (four), retired gunboats (nine), and three former Russian icebreakers. However, the largest group of special purpose vessels in World War I were civilian vessels pressed into service as submarine decoys; some 116 of the more than 200 decoy vessels in service were classified as SSVs to preserve secrecy about their function.
During the Second World War, the Royal Navy equipped nine submarine decoy ships, which were classified as SSVs; this category also included ships such as Golden Eagle, an anti-aircraft paddle steamer, and Glengyle, a fast supply vessel. Probably the most famous special purpose vessel of the Second World War was HMS Fidelity, home of the Independent Group of Fighting Frenchmen led by former French naval officer Jack Langlais. Fidelity carried out several covert missions under the auspices of the British Special Operations Executive before being fitted out as a depot ship for an amphibious raiding force of Marine Commandos. Fidelity was torpedoed and sunk while serving as part of Convoy ON 154, bound for the Far East.
