Dark-class patrol boat
The Dark class, or Admiralty "Type A", were a class of eighteen fast patrol boats that served with the United Kingdom's Royal Navy starting in 1954. All were named with a prefix of 'Dark'. The class could be fitted as either motor gun boats or motor torpedo boats, depending on the type of armament carried. They were the only diesel engined fast patrol boats in the Royal Navy. The class was fitted (along with the Nasty class) with the Napier Deltic two-stroke diesel engine. This was of unique layout, an opposed-piston engine with  a triangular layout of three banks, 18 cylinders in total. Construction. The boats were constructed with alloy framing and wooden decks and skin. The exception was "Dark Scout" which had all aluminium decks, skins and frames. Originally 27 units were ordered by the admiralty from seven builders. Nine were eventually cancelled in 1955, including "Dark Horseman" which at the time was partially completed and on the stocks in the builders yard. The all-aluminium version was exported to Burma (five units), Finland (two units), and Japan (one unit) by builders Saunders-Roe. Design. 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 . For a short while, a compromise half grey/half black combination was used. Fate. An Admiralty decision in 1957 took nearly all fast patrol boats out of commission, with nine of the new "Dark-class" to be laid up. 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 special boat squadron was nominated, but it did not include any of the "Dark-class". Several of the ships were sold to Wessex Power Units for sale onto the Italian Customs Service (8 hulls) in February 1966. Two were used for target practice, with "Dark Gladiator" sunk by HMS "Amazon" and HMS "Naiad" off Portland in December 1975. At least two, "Dark Clipper" and "Dark Fighter", managed to survive up to as recently as June 2001 when they were broken up in Malta. Legacy. The Dark class would be the final  commission of this quantity for patrol boats of this size and speed. The following classes had greatly reduced numbers with the numbering only two vessels and numbering only three. A similar hull design was used by Saunders-Roe in a prototype, "R-103", which led to the development of the experimental hydrofoil, , for the Royal Canadian Navy.