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Note: This is a sub-section of Rolls-Royce
The Peregrine was an 885 hp liquid-cooled V-12 aircraft engine designed in the early 1930s. It was essentially a "rationalized" version of their Rolls-Royce Kestrel, which had seen widespread use.
During the 1930s the use of superchargers to increase the effective displacement of an aircraft engine came into common use. Charging of some form was a requirement for high-altitude flight, and as the strength of the engines improved there no reason not to use it at all times. The introduction of such "ground level" supercharger to the Kestrel along with several design changes improved the power-to-weight ratio considerably, and it was generally felt that the resulting Peregrine would be the "standard" fighter engine for the upcoming war. Two Peregrines bolted together on a common crankshaft would produce the Rolls-Royce Vulture, a 1,700 hp X-24 which would be used for bombers.
As it turned out, aircraft designs rapidly increased in size and power requirements to the point where the Peregrine was simply too small to be useful. Rolls' internal project to "fill in the gap" between the Peregrine and Vulture resulted in the Rolls-Royce Merlin, which annihilated any demand for the smaller, less powerful Peregrine. The demand for the Merlin overshadowed development of the Peregrine and resources for it were cut back as attempts were made to quickly bring the Merlin into service.
In the end only two aircraft used the Peregrine, the Westland Whirlwind and the second prototype of the Gloster F9/37, both twin-engine designs – the prototype F9/37 had used radial Bristol Taurus. The Ministry requirement for the F9/37, a cannon-armed fighter (the Hurricane and Spitfire were armed with machine guns only at this point), was curtailed and there was no further progress with the design. The Whirlwind, despite having excellent low-altitude performance, proved uneconomical compared with single-engined fighters, and also suffered as a consequence of the Peregrine reliability problems. Low production rates of the Peregrine caused delays in delivery to squadron use.
While reliability problems were not uncommon for Rolls-Royce's new engine designs of the era, the company's testing department was told to spend all of their time on developing the more powerful Merlin to maturity. As a result of the Merlin's priority, the unreliable Peregrine was abandoned, its production ending in 1940. Other cannon-armed fighters were becoming available and the Whirlwind was tightly designed around the Peregrine so changing to a different engine was not a feasible option. Only 141 Whirlwinds and a corresponding number of Peregrines were built.
The engine was a 12-cylinder supercharged liquid-cooled Vee aircraft piston engine with a bore of 5 inches (127 mm) and a stroke of 5.5 inches (140 mm) giving a 21.2 litre capacity.