While the Royal Navy abandoned the idea of large scale coastal forces in 1957, it maintained a small force of three boats, the Coastal Forces Trials and Special Service Squadron, to maintain proficiency in operations of fast patrol boats if the need arose in the future, and to act as targets for training the fleet in tactics against hostile fast patrol boats.

[1] Propulsion was by two Rolls-Royce Proteus gas turbine engines rated at a total of 8,500 shaft horsepower (6,300 kW) and two Foden diesel engines rated at 240 brake horsepower (180 kW) arranged in a combined diesel and gas (CODAG) arrangement and driving two propeller shafts.

[5] The ships were unarmed, but were designed so that a gun or missile armament could be fitted if needed, while a third Proteus could be added for improved speed.

[5] Once initial teething problems associated with the settings for the transom flap were resolved, the boats met performance requirements.

[1][6] The three boats were laid up ashore and put on the disposal list in 1981,[1][4] and were later sold to Greek buyers.