Nine were eventually cancelled in 1955, including Dark Horseman which at the time was partially completed and on the stocks in the builders yard.

[4] With no previous experience of using diesel engines in vessels of this size, it was not fully understood how dirty they would get from the exhaust fumes.

Originally launched in the normal Royal Navy grey, they eventually had their hulls painted completely black to disguise the staining from exhaust emissions .

On 20 December 1960, the Admiralty stated that the Coastal Forces would not be completely abandoned in case it needed to be expanded in the future.

A similar hull design was used by Saunders-Roe in a prototype, R-103, which led to the development of the experimental hydrofoil, HMCS Bras d'Or, for the Royal Canadian Navy.