Editing Rolls-Royce Merlin (section)

===Origin===
In the early 1930s, Rolls-Royce started planning its future aero-engine development programme and realised there was a need for an engine larger than their 21-litre (1,296&nbsp;cu in) [[Rolls-Royce Kestrel|Kestrel]], which was being used with great success in a number of 1930s aircraft.<ref>Rubbra 1990, p. 64.</ref> Consequently, work was started on a new {{convert|1100|hp|kW|abbr=on}}-class design known as the PV-12, with PV standing for ''Private Venture, 12-cylinder'', as the company received no government funding for work on the project. The PV-12 was first run on 15 October 1933 and first flew in a [[Hawker Hart]] biplane ([[United Kingdom military aircraft serials|serial number]] ''K3036'') on 21 February 1935.<ref name="Lumsden203">Lumsden 2003, p. 203.</ref> The engine was originally designed to use the [[Radiator (engine cooling)#Evaporative cooling|evaporative cooling]] system then in vogue. This proved unreliable and when [[ethylene glycol]] from the U.S. became available, the engine was adapted to use a conventional liquid-cooling system. The Hart, as a Merlin [[testbed]], completed over 100 hours of flying with the Merlin C and E engines.<ref>Mason 1991, p. 168.</ref>

In 1935, the [[Air Ministry]] issued a specification, [[List of Air Ministry specifications|F10/35]], for new [[fighter aircraft]] with a minimum airspeed of {{convert|310|mph|km/h|abbr=on|lk=on}}. Fortunately, two designs had been developed: the [[Supermarine Spitfire]] and the [[Hawker Hurricane]]; the latter designed in response to another specification, F36/34.<ref>McKinstry 2007, p. 53.</ref> Both were designed around the PV-12 instead of the Kestrel, and were the only contemporary British fighters to have been so developed. Production contracts for both aircraft were placed in 1936, and development of the PV-12 was given top priority as well as government funding. Following the company convention of naming its piston aero engines after birds of prey, Rolls-Royce named the engine the ''[[Merlin (bird)|Merlin]]'' after a small, Northern Hemisphere falcon (''Falco columbarius'').{{#tag:ref|The naming tradition was started by managing director, [[Claude Johnson]], in 1915 with the Eagle, Hawk and Falcon engines. There is no connection to King Arthur's [[Merlin (wizard)|legendary magician.]]|group=nb}}<ref name=Gunston137>Gunston 1989, p. 137.</ref>

Two more Rolls-Royce engines developed just prior to the war were added to the company's range. The {{convert|885|hp|kW|abbr=on}} [[Rolls-Royce Peregrine]] was an updated, [[supercharged]] development of their V-12 Kestrel design, while the {{convert|1700|hp|kW|abbr=on}} 42-litre (2,560 cu in) [[Rolls-Royce Vulture]] used four Kestrel-sized [[cylinder block]]s fitted to a single [[crankcase]] and driving a common crankshaft, forming an [[X24 engine|X-24]] layout.<ref>Rubbra 1990, p. 139.</ref> This was to be used in larger aircraft such as the [[Avro Manchester]].<ref name="Lumsden2003 p198, 200">Lumsden 2003, pp. 198–200.</ref>

Although the Peregrine appeared to be a satisfactory design, it was never allowed to mature since Rolls-Royce's priority was refining the Merlin. As a result, the Peregrine saw use in only two aircraft: the [[Westland Whirlwind (fixed wing)|Westland Whirlwind]] fighter and one of the [[Gloster F.9/37]] prototypes. The Vulture was fitted to the [[Avro Manchester]] bomber, but proved unreliable in service and the planned fighter using it – the [[Hawker Tornado]] – was cancelled as a result.<ref>Lumsden 2003, p. 200.</ref> With the Merlin itself soon pushing into the {{convert|1500|hp|kW|abbr=on}} range, the Peregrine and Vulture were both cancelled in 1943, and by mid-1943 the Merlin was supplemented in service by the larger [[Rolls-Royce Griffon|Griffon]].<ref>Rubbra 1990, p. 118.</ref> The Griffon incorporated several design improvements and ultimately superseded the Merlin.