The Rolls-Royce Merlin Aircraft Engine: P-51 Mustang Power Defeated the Luftwaffe

The North American P-51 Mustang was the best fighter airplane in World War II. It became available to the U.S. fighter command as a potent package in enough time to tilt the air war with Germany in the Allies’ favor. I wrote about the justly-famous P-51 in a previous post (July 6, 2016). That post can be found in my home page archives. In it, I referred to the Merlin V-12 power plant which, when finally coupled with the great airframe platform from California-based North American Aviation, turned a decent performer into an iconic fighting airplane.

While “Rolls-Royce” on this engine clearly denotes an English heritage, the same can, surprisingly, be said of the P-51 itself. Designed and built by North American Aviation in Los Angeles, California, the airplane’s genesis actually emanated from England. The P-51 began as a specification provided to North American by the British Purchasing Commission early in 1940. Incredibly, the first prototype appeared on September 9, 1940, a mere 102 days after the contract with North American was signed. The NA-73X airframe first flew on October 26, 1940.

Originally designed for the British Allison V-1710 engine, the Mustang prototypes demonstrated disappointing performance at altitudes above 15,000 feet. The B-17 and B-24 bombers of the Eighth U.S. Air Force typically cruised over 20,000 feet on their bombing missions into Germany from bases in England. During the Battle of Britain in mid-1940, the German Luftwaffe was already flying their front-line fighter, the Messerschmidt 109. The Me 109 and the Focke-Wulf 190 would both prove to be a significant threat to Allied bombers in the skies over Germany throughout the war. Despite Britain’s just-in-time introduction in 1940 of their own top-line fighter, the Supermarine Spitfire, the Me 109 still had advantages over it and the older Hawker Hurricane by way of its firepower and its fuel-injected engine. The Messerschmidt had, in addition to 50 caliber machine guns, a 20 mm cannon firing through the spinner of its propeller. That deadly weapon coupled with the much longer firing-burst capability of its guns gave the Me 109 a significant advantage. The Hurricane and the Spitfire had carbureted engines with a typical float-chamber in the fuel system which caused the airplanes to hesitate when abruptly put into an evasive dive maneuver. The fuel-injected 109s had no such problem and could easily overtake their prey on the way down.

The major problem faced by the U.S. Eighth Air Force bomber command by 1942 was the vulnerability of its B-17 and B-24 heavy bombers after leaving their bases in the English countryside and entering German air space. The B-17 “Flying Fortress” was aptly named given the eventual array of thirteen 50 caliber machine guns in eight strategic locations around the aircraft. Early in the war, it was believed that bomber formations of aircraft with that degree of armament would be quite capable of protecting themselves from German fighter interceptors who came up to meet them over German territory. That assumption quickly proved very erroneous as losses mounted.

The solution? Provide fighter escorts for the bombers. Prior to the introduction of the P-51 in late 1943, that assignment was handed to fighter wings typically flying the Republic Aviation P-47 Thunderbolt. The P-47 had two major problems. To begin with, the airplane had a short fuel-limited range which forced it to turn back and abandon its escort duties soon after entering German airspace. That, of course, was precisely when the bomber formations would most likely encounter German fighter resistance. Besides, the chunky P-47 suffered severe disadvantages in aerial combat with the more agile and faster Me 109 and Focke-Wulf 190 German fighters. Bomber losses were severe from the combination of aerial flak guns and German interceptors, culminating in the disastrous bombing raid on Regensburg, Germany, where sixty bombers were lost in one day – some 600 men.

Enter the P-51 Mustang in late 1943 whose horsepower, speed, agility, and high-altitude performance provided a palpable advantage over German counterparts thanks to its supercharged Merlin engine which had replaced the original Allison V17-10 powerplant. With the airplane’s inherently large fuel capacity and an added pair of drop-tanks beneath its wings, the P-51 could go all the way to the target and back with the “heavies.” The bomber crews fondly referred to the Mustang escorts as their “little friends.”

Most of the eventual Mustang production of some 15,000 planes was powered by the Rolls-Royce Merlin built under license by the Packard Motor Car company in Detroit. The Merlin engine was also widely used in other notable wartime aircraft including England’s top fighter, the Spitfire. Nothing in the air during the war could match the powerfully effective Merlin/Mustang combination, however.

I recently watched a wartime documentary on the momentous effort to design and ramp up production of the Merlin engine in England during the early phases of WW II. This was a huge wartime effort on the part of the English who faced the possible invasion of their country and the subjugation of Europe at the hand of Hitler’s Germany. The film was totally enlightening and engrossing – so many history and social lessons to be derived from the can-do spirit of the English.

My wife and I recently saw the movie, The Darkest Hour, which portrayed Winston Churchill’s lonely desperation in 1939/1940 as the destiny of England and, indeed, all of Europe became increasingly problematic. Fact is always stranger and more dramatic than fiction, and this fine movie drives home the point. So much hung in the balance, a balance which finally tilted favorably to the Allies on the knife-edge of numerous pivotal decisions and efforts. The Merlin engine and the P-51 Mustang airframe from North American Aviation were two of those very decisive factors which ultimately doomed Hitler – especially as combined together in the final P-51 designs. In 1945, many of Germany’s major cities had been reduced to rubble by Allied bombers based in England which, thanks to the Mustangs and their intrepid pilots, could now reach their targets.

I will close by calling upon a recollection from my earlier post on the iconic P-51 Mustang when the Collings Foundation brought their Wings of Freedom touring air show to nearby Moffett Field. My two young grandsons and I stood close by on the tarmac as their P-51, Betty Jane, prepared to fly.

Firing-Up the Big Merlin-Packard Engine of Betty Jane

As my grandsons and I stood outside the roped area, a mere 50 feet from Betty Jane, the pilot fired up the big Packard-built twelve-cylinder engine sporting a large, four-bladed propeller. The pilot yelled “clear” from the cockpit, the big prop started to turn, and the engine came to life after belching smoke and the usual series of backfires. The engine sounded a throaty roar as Betty Jane moved out toward the taxi-way. My grandsons held their ears…I did not and drank it all in. In my mind’s eye, I could imagine the emotions of a pilot on the flight line at Leiston, England, bringing that big engine to life en-route to yet another bomber escort mission over Germany in 1944/45. Despite the huge war effort and all the backing provided by the allies for combat flight operations, out there on the flight line, as the engine coughed, sputtered, roared to life, and the canopy closed, it was one man in one machine – very far from home. The pilot was about to face the uncertainties of weather, navigation, and his enemy counterparts who would be out there, somewhere, waiting for him and the opportunity to shoot him and his machine out of the sky.

For me, it is difficult to conjure up a more daring and exhilarating human experience than that encountered by those flyers in World War II. For them at the time, there surely seemed nothing “romantic” about the deadly task they faced – only a sense of high adventure and “what the hell, I hope I come back from this one!” I have read the late-life accounts of some who flew Mustangs against the German Luftwaffe and lived to tell about it. Despite some surely ugly recollections of killing and death which stubbornly remain, time dulls many of the sharp edges – as it always does – for these men. These flyers are revered by the public for their courage, daring, and skill during wartime, and that is appropriate. Despite old age and the challenges of settling down after flying, these warriors possess indelible and precious memories of that time in their young lives when they and their machines defied the great odds stacked against them. Those who flew the P-51 Mustang, to a man, relate their admiration of and gratitude to the airplane that saw them through.

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