Rolls-Royce
Merlin Engine

Arguably one of the best engines ever to be widely produced during World War II, the Rolls-Royce Merlin engine was without a doubt one of the most successfully employed aircraft engines in history.  During World War II, the Merlin could be found on any number of different types of allied aircraft, from fighters to bombers, but it was when the engine was introduced to the P-51 Mustang that it changed the face of the war.

The Merlin is a 12 cylinder, 60º “V”, 27 liter, liquid cooled piston aircraft engine capable of mustering 1700 horsepower.  The first Merlin was built in 1936 by Rolls-Royce to fill the 700 and 1,500 hp gap in their aero engine line.  Originally designed as the 1,100 hp PV-12 (PV for Private Venture), the first Merlin only saw a production run of 172 before the adoption of the Merlin II.  The difference between the two was the angle of the inlet valves to the cylinders; the Merlin I had the valves at a 45º angle to the cylinder where as the Merlin II had a conventional flat head arrangement with the valves being parallel to the cylinder.  These early Merlin engines were considered to be relatively unreliable, but thanks in part to a quality control program developed by Rolls-Royce, the Merlin matured and was able to run at full power for eight hours at a time with no problems.

With the introduction of the Merlin in 1937, Rolls-Royce employed fewer than 7,000 people.  By the end of World War II, the company had more than 55,000 employees and produced more than 100,000 Merlin engines (an additional 60,000 Merlins were built under license by Packard in the United States).  19 different types of aircraft were outfitted with Merlin engines including the Spitfire, P-51, Mosquito, Lancaster, and the P-40L with power outputs ranging from 1,000 hp to over 2,000 hp in the Merlin 66.

In 1940 and agreement was reached between the Packard company in Detroit and Rolls-Royce that would allow Packard to produce Merlin engines.  These American built engines were produced by an assembly line, rather than the Europeans method of meticulously hand building each engine, but surprisingly enough were just as well made and actually improved the maintainability of the engine by allowing easier use of interchangeable parts (as opposed to custom finished ones).

Because of the Merlin’s dynamic two-speed, two-stage (in later models) engine driven supercharger, it was capable of delivering high power at altitudes in excess of 30,000 feet.  This made the engine the ideal choice for one of the newest American and British fighters, the P-51 Mustang.  The first of the Mustangs, the P-51A’s, were outfitted with Allison V-1710 engines.  These engines, due to GE’s inability to produce a sufficient quantity, lacked the General Electric turbochargers that would enable the P-51 to have suitable high altitude performance.  The P-51A was forced to stay relatively low because of this (below 20,000 feet) and was not able to fly escort for the allies’ high altitude bombers.  In 1943, the next model of the Mustang took to the skies with a Packard Merlin V-1560 and outperformed the P-51A in all aspects.  The rate of climb had been doubled at all altitudes, and the P-51B’s level flight speed at 29,800 feet was 441 mph, a full 100 mph faster than the P-51A at that altitude.

The Mustang went on to strike fear into the heart of the Axis powers with its newfound ability to fight just as well up high as it could down low.  According to the pilots who flew them, the new Merlin-powered Mustangs were some of the most honest and well-performing aircraft they had ever flown. These P-51s were also some of the only piston powered airplanes that would ever shoot down enemy jets.  When the Germans introduced the ME-262 jet fighter, it was the P-51 Mustang with a Merlin under the hood that kept the plane in the fight and led to more than several ME-262 (as well as other jets) losses to the P-51’s six .50 caliber machine guns.  The Mustang had become the United States’ premier air superiority fighter in the European Theater of Operation in the last few years of the war, and thusly securing the Allied victory over Germany.

After World War II, the Merlin found a niche in boat racing when the boat Slo-mo-shun V took first place at the Seattle Gold Cup Race in 1954.  Merlins continued to be used in boat racing all the way through the 1980s with great success.  The Merlin engine also saw installation on a very few amount of automobiles.  John Dodds, with assistance from Paul Jameson, fitted the engine and chassis to a Ford Capri body and called it “The Beast.”  At one point, “The Beast” was listed in the Guinness Book of World Records as the most powerful road car.  A small handful of other Merlin powered cars were developed, but no matter what other vehicles the Merlin was installed in, it was the Merlin-engined P-51 Mustang that made the engine one of the most well-known, beautifully engineered pieces of equipment ever designed by Rolls-Royce.