The legendary engines that won World War II

Jay Leno has a truly historic engine that he wants to show you: A Merlin 1650-1 engine used in fighters like the P-51 Mustang and Lancaster Bombers used across Europe to drive Germany back toward Berlin.

The engine got its start before the war. It underwent initial testing in 1933 and first took to the skies in 1935. Early models generated about 800 horsepower but increasing requirements in the pre-war years caused Rolls Royce to keep redesigning it, giving it more power and reliability.

The De Havailland Mosquito was powered by two Merlin engines.

(Photo by Wallycacsabre, CC BY 2.0)

Aircraft manufacturers in England kept reaching for the Merlin for their new designs. In 1939, the first production Spitfire rolled off the line packing a Merlin Mk. II engine capable of 1,030 horsepower.

This engine would go on to be used in everything from the Lancaster bomber, which sported four of these beasts, to the De Havilland Mosquito and the P-51 Mustang.

The engine was constantly upgraded with new superchargers and designs, increasing horsepower to 1,150 then 1,480 then 1,515. More importantly, the engines got upgrades in reliability and airflow, helping pilots win fights in altitudes low and high.

The Lancaster bomber boasted four of the massive Merlin engines.

(Royal Air Force photo by Fleet Lt. Miller, IWM)

The low-altitude upgrades would prove essential during the Battle of Britain where English and German planes clashed in fights as low as 6,000 feet.

As it was, the Merlins suffered one big problem that came up during the Battle of Britain and other struggles: it used a carburetor while contemporary German engines were fuel-injected. This meant that the Merlin had a tendency to cut out during dives while the fighters they were opposing did not.

Still, the engine was a literal lifesaver for RAF pilots, and both the Brits and Americans wanted to buy more of them.

A P-51 flies over Virginia. The P-51 was first built with an Allison engine but quickly transitioned to the Merlin with great results.

(U.S. Air Force photo by Tech Sgt. Ben Bloker)

Britain inked a deal with Ford motor company to start mass producing the engine on the American side of the Atlantic, but Ford later backed out of the deal. The offer was made to Packard, then a luxury car brand in the U.S., who turned out their first Merlin engines in August 1941.

It's one of these early Packards that Leno is showing off in his garage. They were delivered across the Atlantic both in boxes and already installed in planes like the P-51.

The P-51 was originally ordered by the Royal Air Force in 1940 and sported an Allison engine that produced 1,200 hp, but proved unreliable above 15,000 feet. Since it was supposed to escort bombers, that was a huge issue. The switch to the Merlins greatly increased their power and altitude ceilings.

And, in a lucky coincidence, the Merlin changed the center of gravity of the plane, shifting it slightly back. The engineers added a fuel tank to the front to level it out, also increasing the plane's range.

World War II buffs love the engine for its effect on the war, but gearheads like Leno can find a lot to love in the engine's massive power output and throaty sound. As Leno points out in the video below, he actually bought two cars built around the Merlin engine — and both are massive hotrods.