In need of fighter aircraft in 1940, Britain contacted North American Aviation about the possibility of producing Curtiss P-40 aircraft under license. Believing that they could create a better product, North American designed and built an entirely new fighter in less than four months. The result, the P-51 Mustang, became an icon of military aviation and one of the most successful fighter designs created.
By Seth Marshall
By the spring of 1940, it had become apparent to the British that the attrition rate of their fighter aircraft over the Western Front and other theaters was going to be higher than the British aircraft industry was able to cope with. Pre-war orders for foreign aircraft were not uncommon, and the practice only increased following the outbreak of the war. Having previously ordered large numbers of Curtiss P-40 Warhawks, then the most modern US fighter, the British Air Purchasing Commission was searching for other American aircraft companies that could produce the aircraft under license. In April 1940, the Commission contacted North American Aviation, a relatively new company in the American market. While the British were hoping to obtain more P-40s, the president of the company, James H. Kindelberger, said that his company could design a new aircraft built around the same engine powering the Warhawk, the Allison V-1710. The British eventually agreed to the proposal, and design work began immediately.
What would become the P-51 was initially referred to as the NA-73X. The chief designer of the new aircraft was Edgar Schmued, a German emigrate who had arrived in the US in 1930. Also on the design team was Edward Horkey, an aerodynamics specialist. The team came up with an airframe to fit around the Allison engine that differed greatly from the Warhawk. The design team strove to make the plane as aerodynamically clean as possible to increase speed. Additionally, in a break from conventional wing designs of the time, the NA-73X was given a laminar flow wing. In previous designs, the wing’s maximum thickness was achieved close to the leading edge of the wing. The laminar flow wing, by contrast, positioned the thickest section of the wing more towards the halfway point of the wing, reducing turbulent airflow across the wing. This had the combined effect of increasing speed and range. Additionally, the Mustang featured squared wingtips, which were found to have slightly less drag in wind tunnel testing than contemporary rounded wingtips. On September 9, 1940, 102 days after North American had signed its contract with the British, the NA-37X was rolled out of the factory- a remarkably short period of design and initial construction even in that period- minus its engine and armament. The engine arrived in October, and on the 26th of that month, the prototype made its first flight and achieved a speed of 382mph, 25mph faster than the P-40.
It was not until May 1, 1941 that the second aircraft, the first production model, was rolled out. By this time, the new fighter had acquired the name “Mustang” from the British. The third Mustang was shipped to Britain in the fall of 1941 and made its first flight on October 26th after being equipped with VHF radio, a gunsight, and other equipment. Testing continued to take place through late 1941 and early 1942 with the Air Fighting Development Unit located at RAF Duxford. During this time, RAF pilots found that while the Mustang was fast and highly maneuverable, its performance degraded at altitudes above 15,000 feet, due to the Allison engine not functioning as well at higher altitudes. While this made the Mustang Mark I (the British used Marks to differentiate models instead of letters, which was preferred by the USAAF) unsuitable for interception and escort missions, the RAF accepted the aircraft for use as a photo-reconnaissance plane and tactical fighter bomber. The first Mustang Is began arriving in RAF squadrons in early 1942, with the first missions taking place that spring. The first operational loss of a Mustang occurred over France in July 1942, and the fighter scored its first kill on August 19, 1942, when an American pilot flying for the Royal Canadian Air Force, Hollis H. Hillis, shot down a German fighter in support of the ill-fated Dieppe raid.
Not long after North American had signed its contract with the British to produce the Mustang, the United States Army Air Corps (known after mid-1941 as the United States Army Air Forces) agreed to let exports of the Mustang proceed on the condition that North American deliver two planes to the USAAC for evaluation. Subsequently, the ninth and tenth Mustangs built were given to the USAAC and redesignated as XP-51s. After a period of evaluation, the USAAF decided to order 310 P-51As and 300 A-36As, dive-bomber variants of the P-51A with dive-brakes and bomb racks beneath the wings, in 1942. Additionally, a number of Allison-engined Mustangs were converted to F-6As, the USAAF photo-reconnaissance version of the fighter. The went into action with the USAAF in March 1943, when three dozen F-6As with the 111th and 154th Observation Squadrons arrived in Tunisia to provide reconnaissance support during the closing stages of the North African campaign. Other P-51As would see combat elsewhere in the Mediterranean Theater as well as in the China-Burma-India Theater.
While the P-51A was a definite improvement over the P-40 Warhawk, it was felt that better performance could be gained through the substitution of a different powerplant. In 1942, four Mustangs were modified by the British to use the Rolls-Royce Merlin engine, the same engine that powered the Supermarine Spitfire of Battle of Britain fame, as well as the DeHavilland Mosquito and Avro Lancaster. American engineers performed similar tests with two Mustangs powered by Packard-built Merlin engines. In order to accommodate the power of the new engine, which boasted 1,695hp, the airframe was strengthened; the radiator, located on the belly of the aircraft, was deepened, and the carburetor was moved from on top of the nose to below it. The results revolutionized the Mustang’s performance. Speed was increased to 426mph at 24,000ft. Tests comparing the Mustang to the Spitfire demonstrated that the Mustang had far greater range and now had excellent high altitude performance. The newly-redesigned Mustang arrived at an apt time for the USAAF.
In 1942, the USAAF had begun its daylight bombing campaign against Germany. Convinced that daylight precision bombing was the proper way to wage aerial warfare against the Germans, the USAAF had begun sending its heavy bombers deep into Reich territory. However, earlier USAAF and RAF fighters, namely the P-47 Thunderbolt and Spitfire, lacked the range to escort the bombers all the way to their targets; upon reaching the German frontier, the friendly escorts were forced to turn back for their bases. It was after this point that Luftwaffe fighters attacked the bomber formations. During 1943, losses increased steadily, culminating in the second raid on the ball-bearing production facilities at Schweinfurt, Germany on October 14, 1943. Known thereafter as Black Thursday, out of the 350 heavy bombers sent to attack both Schweinfurt, 60 B-17s were shot down by fighter attacks over Europe, another five had crashed in England and 17 were written off on their return as too badly damaged to ever fly again. With a mission loss rate of 26%, the second Schweinfurt raid was the costliest raid the Eighth Air Force mounted- in return, the Luftwaffe had lost around 40 fighters to the guns of the bomber formation. With the losses on Black Thursday as well as preceding raids, the Eighth Air Force was forced to put its bomber offensive on hold until replacement aircraft could arrive and more adequate fighter protection be provided.
With the introduction of the Merilin-powered Mustang, the solution to the problem of fighter escort had arrived. Carrying two releasable drop-tanks full of fuel, Mustangs were capable of escorting the bombers all the way to their targets and back. Despite this, the first USAAF P-51Bs to arrive in England were assigned to the 354th Fighter Group with the Ninth Air Force in October 1943, which was slated to primarily function in the tactical role during upcoming operations. Eventually, it was decided that most of VIII Fighter Command’s squadrons would be equipped with the P-51- squadrons already equipped with the P-47 and P-38 would eventually transition to the new Mustang. The Ninth Air Force would ultimately be equipped primarily with P-47s, which were better suited to the ground-attack role, though it also retained two groups of P-51s.
By the spring of 1944, the definitive version of the Mustang, the P-51D, began to arrive in England. This new Mustang had a cut down rear fuselage and bubble-shaped canopy which greatly improved pilot visibility. Additionally, two .50 caliber machine guns were added, one in each wing, making a total of six machine guns. With a maximum speed of 437mph and range of 1650 miles with external tanks, the P-51D became the premier fighter of the Eighth Air Force. Combined factors of increasingly better pilot training in the USAAF, decreasing pilot training and effectiveness in the Luftwaffe, and excellent performance allowed Mustang pilots to claim 4,950 aircraft shot down during the war, more than any other Allied fighter. Dozens of Mustang pilots would become aces, a special status reserved for those who had shot down five or more enemy aircraft. Among the Mustang’s well-known pilots was then Captain Charles E. “Chuck” Yeager, who would go on the break the sound barrier in 1947- serving with the 357th Fighter Group, Yeager shot down 12.5 planes. Describing a typical mission, William Lyons later recalled a mission he flew on November 21, 1944 as a 20-year old 1LT with the 355th Fighter Group:
“We’re about 12 minutes from Misburg. The 357th’s Red flight is arrayed to the right of our bomber box, and my Yellow flight is to the right of Red, with the Blue and Green flights to the left a mile behind us. Someone calmly radios, “Bogeys at 10 o’clock” (bogeys are unidentified aircraft; bandits are enemy aircraft). Another calls, “Bogeys, 2 o’clock high.” I can see little black dots ahead, and then I hear, “Bandits, 12 o’clock!” followed by “Bandits at 3!”—Kelley’s voice. The dots rapidly enlarge and multiply across the horizon. They expand into 75 to 100 Me-109s, closing fast on the front of the bomber stream. I quickly switch to the rear internal tank, drop my two external tanks and flick on the gun switch. Fred jettisons his externals and pivots right, toward 1 and 2 o’clock, where the gaggle of Germans is densest. We head into them full throttle—our combined closure speed some 600-700 mph—and go right through them, both of us narrowly avoiding crashing into enemy fighters. Our guns are firing, though I see no hits. When Fred whips back, I’m glued to his tail, right behind and to one side. Now Fred’s firing at a 109 that’s in a diving turn under the bombers, following him down while hitting him. Trailing heavy smoke, that one’s done for. Out of the corner of my eye I see a bomber burst apart, and tiny forms falling out. No parachutes are opening. Fighters from both sides are swirling contrails all over the place. Then another bomber falls, with black smoke coming from the left-wing engines. Fred latches onto another 109, both of them diving and twisting down until the 109 loses half its right wing. That’s two for Fred. We’re down to 5,000 feet. My heart is pounding, and I’m drenched in perspiration. On the radio we hear urgent shouts and warnings, some sounding close, others way off. More enemy fighters are hitting the bombers, though I can’t see them. Just now the sky seems empty of planes except our Yellow flight and the bomber stream far above us. Suddenly Kelley yells, “Yellow 2, SIX!” I pull back sharply and left, then I hear Barney Barab slowly saying, “I…got…him.” Looking back, I glimpse Barab following down a smoking Me-109, with Kelley trailing them. Then it hits me: Yellow 3 and 4 just saved my life. As we climb back toward the bomber stream, a 109 dives straight down almost directly ahead of us. Fred does a split-S to follow him, and during our dive we spot three more 109s on the deck, heading east. Fred corkscrews toward the trailing plane, with me following, but his dive is too steep and he has to pull out early. His target whips to the left while the leading 109 below turns right and comes in behind Fred, shooting up at him 200 to 300 yards ahead of me at about 30 degrees. I fire, landing many strikes on the German. There’s smoke and the 109 goes out of control, crashing into the deck. The rest of the 109s then disappear, heading east. I follow Fred’s low, climbing circle, and we’re joined by Yellow 3 and 4. At 500 feet Fred turns due west: We’re heading home. Kelley is flying funny, though his speed seems OK. Engine oil blackens his fuselage, but we can’t tell whether there’s damage to his plane. Now he drifts off formation, shifting erratically. Something’s wrong. The three of us radio him, but there’s no answer. Barab goes in close to take a look. Suddenly Kelley swerves into him, and they both explode in a cloud of aluminum confetti! No possibility of survival. Horrible. Fred and I circle around the silvery shards slowly floating down, looking for any positive sign, but we see nothing hopeful. We head toward home in a grim mood. Our transit over Germany to the North Sea coast is uneventful, though there’s flak over the Frisians. Fred and I are first ones back. I tell my crew chief about Kelley and Barab so he’ll tell their crew chiefs not to expect them.”
Lyons would finish his tour on March 28, 1945 after completing 63 missions with two confirmed kills. The highest-scoring Mustang ace of the war was George Preddy. Previously a P-40 pilot in the Pacific, Preddy was reassigned to Europe following serious injuries resulting from a collision with another aircraft. Flying with the 352nd Fighter Group, Preddy would shoot down 25 German aircraft from late April 1944 to December 25, 1944. On one memorable occasion, August 6th, Preddy took off on a mission with a severe hangover from a party that had lasted until the early hours of the morning. Despite his condition, Preddy shot down six German planes that day. However, his luck ran out on December 25th, when he was shot down by a friendly anti-aircraft unit as he was pursuing a Luftwaffe fighter and died of his wounds. The most successful Mustang unit was the 4th Fighter Group, commanded by Colonel Donald Blakeslee; the first VIII Fighter Command Group to convert to the Mustang, the 4th shot down 583 planes in the air and destroyed 469 more on the ground.
Outside of Europe, the Mustang saw action in the Pacific. Reluctant to replace his P-38s with Mustangs, 5th Air Force commander Major General George Kenney refused to accept the new fighters. However, the range of the Mustangs ultimately allowed them to escort B-29s on raids against Japan late in the war. Following the captured of Iwo Jima, fighter groups were quickly established on the small island to provide escort for the big bombers. The first B-29 escort mission was carried out on April 29, 1945, when 108 P-51s escorting the Superfortresses to their target.
By the end of the war, the US had produced 15,386 P-51s of all types. Additionally, the Commonwealth Aircraft Corporation in Australia had produced another 200. In the post-war era, Mustangs served in numerous air forces all over the world. Despite the advent of the jet, the Mustang saw heavy use early in the Korean War as a fighter bomber- the P-51 was the only aircraft available in significant numbers that could be sent to the theater quickly, and it served as the USAF’s primary close air support weapon for much of the war. Later in the conflict, the reconstituted Republic of Korea Air Force was given many of the USAF’s Mustangs to fly for their own missions. The P-51 was phased completely out of US inventories when the last Mustangs left the Air Force Reserve and Air National Guard in 1957. Other countries continued to the use the Mustang for decades. Today, the Mustang is a popular sight at air shows. Over 100 P-51s remain airworthy, with many more on static display in museums.
The P-51 Mustang remains one of the most iconic aircraft made, and was one of the best fighter designs produced during World War II. It’s ability to escort heavy bombers all the way to their targets and then out-perform the Luftwaffe fighters which it encountered sealed the fate of the already troubled-Luftwaffe over Western and Central Europe. It’s unmatched record of nearly 5,000 kills cemented its place as the most-successful Allied fighter of the war.
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