How an American license transformed a British engine into a global powerhouse

Wars & Conflicts · Published 16 October 2026 Swipe more like this →

In short: In 1940, a $130,000,000 agreement between Rolls-Royce and Packard changed the course of aerial warfare. By manufacturing the Merlin engine under license in the United States, the Allies secured the high-altitude performance necessary to escort heavy bombers deep into enemy territory.

The Packard V-1650 Merlin was not a new invention, but a sophisticated American adaptation of the British Rolls-Royce Merlin. To meet the massive demand of World War II, the Packard Motor Car Company entered a licensing agreement in September 1940. While the British were establishing 'shadow factories' in cities like Glasgow and Manchester, the American production provided the necessary scale. The first Packard-built engine, the V-1650-1, successfully ran in August 1941.

Engineering refinements made the American version distinct. Early models featured modified crankshaft bearings, replacing a copper-lead alloy with a silver-lead combination and indium plating to improve load-carrying capabilities. Later, more advanced versions like the V-1650-3 utilized a two-stage supercharger. This mechanism used two separate impellers on a single shaft, driven at a gear ratio that could shift from 6.391:1 to 8.095:1 via a hydraulic gear change. This allowed the engine to maintain high power even as air density dropped at altitude.

The engine's performance was a feat of thermal management. Compressing air through two stages could raise temperatures as high as 205 °C (401 °F), risking engine detonation. To prevent this, engineers integrated an intercooler and used a pressurized 70% water and 30% ethylene glycol mixture to cool the intake. This technology enabled the engine to develop over 1,270 horsepower even above 30,000 feet. This reliability turned the North American P-51 Mustang into a legendary long-range escort, capable of protecting bombers on missions to Germany and Japan.

The legacy of the V-1650 extends far beyond the war. Many surplus engines were repurposed for air racing in prestigious events like the Cleveland and Thompson Trophies. Today, modified Merlins continue to push boundaries in unlimited class racing, with some engines reaching up to 3,800 horsepower using water-methanol injection.

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