North American P-51 Mustang

The North American Aviation P-51 Mustang was an American long-range, single-seat fighter and fighter-bomber used during World War II, the Korean War and other conflicts. The Mustang was conceived, designed and built by North American Aviation (NAA) in response to a specification issued directly to NAA by the British Purchasing Commission. The prototype NA-73X airframe was rolled out on 9 September 1940, 102 days after the contract was signed and, with an engine installed, first flew on 26 October.

The Mustang was originally designed to use the Allison V-1710 engine, which had limited high-altitude performance. It was first flown operationally by the Royal Air Force (RAF) as a tactical-reconnaissance aircraft and fighter-bomber (Mustang Mk I). The addition of the Rolls-Royce Merlin to the P-51B/C model transformed the Mustang's performance at altitudes above 15,000 ft, giving it a performance that matched or bettered the majority of the Luftwaffe's fighters at altitude. The definitive version, the P-51D, was powered by the Packard V-1650-7, a license-built version of the Rolls-Royce Merlin 60 series two-stage two-speed supercharged engine, and armed with six .50 caliber (12.7 mm) M2 Browning machine guns.

From late 1943, P-51Bs (supplemented by P-51Ds from mid-1944) were used by the USAAF's Eighth Air Force to escort bombers in raids over Germany, while the RAF's 2 TAF and the USAAF's Ninth Air Force used the Merlin-powered Mustangs as fighter-bombers, roles in which the Mustang helped ensure Allied air superiority in 1944. The P-51 was also in service with Allied air forces in the North African, Mediterranean and Italian theatres, and saw limited service against the Japanese in the Pacific War. During World War II, Mustang pilots claimed 4,950 enemy aircraft shot down.

At the start of the Korean War, the Mustang was the main fighter of the United Nations until jet fighters such as the F-86 took over this role; the Mustang then became a specialized fighter-bomber. Despite the advent of jet fighters, the Mustang remained in service with some air forces until the early 1980s. After World War II and the Korean War, many Mustangs were converted for civilian use, especially air racing, and increasingly, preserved and flown as historic warbird aircraft at airshows.

In April 1938, shortly after the German Anschluss of Austria, the British government established a purchasing commission in the United States, headed by Sir Henry Self. Self was given overall responsibility for Royal Air Force (RAF) production and research and development, and also served with Sir Wilfrid Freeman, the "Air Member for Development and Production". Self also sat on the British Air Council Sub-committee on Supply (or "Supply Committee") and one of his tasks was to organize the manufacturing and supply of American fighter aircraft for the RAF. At the time, the choice was very limited, as no U.S. aircraft then in production or flying met European standards, with only the Curtiss P-40 Tomahawk coming close. The Curtiss-Wright plant was running at capacity, so P-40s were in short supply.

North American Aviation (NAA) was already supplying its Harvard trainer to the RAF, but was otherwise underutilized. NAA President "Dutch" Kindelberger approached Self to sell a new medium bomber, the B-25 Mitchell. Instead, Self asked if NAA could manufacture the Tomahawk under license from Curtiss. Kindelberger said NAA could have a better aircraft with the same engine in the air sooner than establishing a production line for the P-40. The Commission stipulated armament of four .303 in (7.7 mm) machine guns, the Allison V-1710 liquid-cooled engine, a unit cost of no more than $40,000, and delivery of the first production aircraft by January 1941. In March 1940, 320 aircraft were ordered by Sir Wilfred Freeman who had become the executive head of Ministry of Aircraft Production (MAP), and the contract was promulgated on 24 April.

The NA-73X, which was designed by a team led by lead engineer Edgar Schmued, followed the best conventional practice of the era, but included several new features. One was a wing designed using laminar flow airfoils which were developed co-operatively by North American Aviation and the National Advisory Committee for Aeronautics (NACA). These airfoils generated very low drag at high speeds. During the development of the NA-73X, a wind tunnel test of two wings, one using NACA 5-digit airfoils and the other using the new NAA/NACA 45–100 airfoils, was performed in the University of Washington Kirsten Wind Tunnel. The results of this test showed the superiority of the wing designed with the NAA/NACA 45–100 airfoils. The other feature was a new radiator design that exploited the "Meredith Effect", in which heated air exited the radiator as a slight amount of jet thrust. Because NAA lacked a suitable wind tunnel to test this feature, it used the GALCIT 10 ft (3.0 m) wind tunnel at Caltech. This led to some controversy over whether the Mustang's cooling system aerodynamics were developed by NAA's engineer Edgar Schmued or by Curtiss, although NAA had purchased the complete set of P-40 and XP-46 wind tunnel data and flight test reports for US$56,000. The NA-73X was also one of the first aircraft to have a fuselage lofted mathematically using conic sections; this resulted in the aircraft's fuselage having smooth, low drag surfaces. To aid production, the airframe was divided into five main sections—forward, center, rear fuselage and two wing halves — all of which were fitted with wiring and piping before being joined. XP-51 41-039, one of two Mustang Is handed over to the USAAC for testing.

The prototype NA-73X was rolled out in September 1940 and first flew on 26 October 1940, respectively 102 and 149 days after the order had been placed, an uncommonly short gestation period. The prototype handled well and accommodated an impressive fuel load. The aircraft's two-section, semi-monocoque fuselage was constructed entirely of aluminum to save weight. It was armed with four .30 in (7.62 mm) M1919 Browning machine guns, two in the wings and two mounted under the engine and firing through the propeller arc using gun synchronizing gear.

While the United States Army Air Corps (USAAC) could block any sales it considered detrimental to the interests of the US, the NA-73 was considered to be a special case because it had been designed at the behest of the British. In September 1940 a further 300 NA-73s were ordered by MAP. To ensure uninterrupted delivery Colonel Oliver P. Echols arranged with the Anglo-French Purchasing Commission to deliver the aircraft, and NAA gave two examples (41-038 and 41-039) to the USAAC for evaluation.

Pre-war doctrine was based on the idea "the bomber will always get through". Despite RAF and Luftwaffe experience, the USAAC still believed in 1942 that tightly packed formations of bombers would have so much firepower that they could fend off fighters on their own. Fighter escort was low-priority, and when an escort fighter was planned in 1941, not considering what the nascent NA-73 design could be developed into – at a time when a heavy fighter with twin engines was considered to be most appropriate, like the Americans' own fast-flying P-38 Lightning for existing types in the USAAF inventory – it would be a heavily up-armed "gunship" conversion of a strategic bomber that would get a chance to prove itself in action. Additionally, a high-speed fighter with the range of a bomber was thought to be an engineering impossibility. Eighth Air Force operations 1942–1943

The 8th Air Force started operations from Britain in August 1942. At first, because of the limited scale of operations, there was no conclusive evidence American doctrine was failing. In the 26 operations flown to the end of 1942, the loss rate had been under 2%. This rate was better than the RAF's night efforts, and similar to the losses one would expect due to mechanical failure.

In January 1943, at the Casablanca Conference, the Allies formulated the Combined Bomber Offensive (CBO) plan for "round-the-clock" bombing – USAAF daytime operations complementing the RAF nighttime raids on industrial centers. In June 1943, the Combined Chiefs of Staff issued the Pointblank Directive to destroy the Luftwaffe's capacity before the planned invasion of Europe, putting the CBO into full implementation. Following this, the 8th Air Force's heavy bombers conducted a series of deep-penetration raids into Germany, beyond the range of escort fighters.

German daytime fighter efforts were, at that time, focused on the Eastern Front and several other distant locations. Initial efforts by the 8th met limited and unorganized resistance, but with every mission the Luftwaffe moved more aircraft to the west and quickly improved their battle direction. The Schweinfurt–Regensburg mission in August lost 60 B-17s of a force of 376, the 14 October attack lost 77 of a force of 291—26% of the attacking force. Losses were so severe that long-range missions were called off.

The outcome of these air battles were extensively studied by both forces. The Luftwaffe felt their primary problem was armament, as their fighters were designed for combat against other fighters and lacked a weapon suitable to quickly knocking down an aircraft as large as the B-17, preferably from beyond the effective range of the bomber formations' heavy defensive firepower, which in a typical USAAF combat box heavy bomber formation could easily number in the dozens to nearly a hundred Browning M2 machine guns. The Luftwaffe responded to this need by fostering the development of heavier, 30mm calibre autocannons like the MK 108, and other weapons, as well as moving twin-engine heavy fighters to the bomber destroyer role that could carry the 37mm and 50mm Bordkanone series of heavy-calibre, auto-loading guns, as well as the BR 21 heavy-calibre unguided rockets that entered service in the spring of 1943. With these changes, along with better command and control needed to direct the large number of aircraft, their forces developed for a return of combat in the spring.

For the US, the very concept of self-defending bombers was called into question. But instead of abandoning daylight raids and turning to night bombing, as the RAF suggested, they chose another path. The solution to defending against the fighters was to escort the bombers throughout their mission with fighters of their own. What was needed was the proper long-range escort fighter, a class that both the RAF and Luftwaffe had tried and failed to successfully fulfill.

The Lockheed P-38 Lightning had the range to escort the bombers, but was only available in small numbers in the European theater due to its Allison engines proving difficult to maintain. Furthermore it was also a very expensive aircraft to build and operate, and was insufficiently maneuverable to successfully take on the Luftwaffe fighters. Adolf Galland thought it "clearly inferior" to the Luftwaffe's own fighters. The Republic P-47 Thunderbolt was capable of meeting the Luftwaffe on more than even terms, but did not at the time have sufficient range. The Luftwaffe quickly identified its maximum range, and their fighters waited for the bombers just beyond the point where the Thunderbolts had to turn back. P-51 introduction

The P-51 Mustang was a solution to the clear need for an effective bomber escort. The Mustang was at least as simple as other aircraft of its era. It used a common, reliable engine and had internal space for a huge fuel load. With external fuel tanks, it could accompany the bombers all the way to Germany and back. Enough P-51s became available to the 8th and 9th Air Forces in the winter of 1943–44.

When the Pointblank offensive resumed in early 1944, matters had changed dramatically. The defence was initially layered, using the shorter range P-38s and P-47s to escort the bombers during the initial stages of the raid and then handing over to the P-51 when they turned for home. This provided continual coverage during the entire raid. The Mustang was so clearly superior to earlier US designs that the Eighth Air Force began to switch its fighter groups to the Mustang, first exchanging arriving P-47 groups for those of the 9th Air Force using P-51s, then gradually converting its Thunderbolt and Lightning groups. By the end of 1944, 14 of its 15 groups flew the Mustang.

The Luftwaffe's twin-engine heavy fighters brought up to deal with the bombers proved to be easy prey for the Mustangs and had to be quickly withdrawn from combat. The Focke-Wulf Fw 190A, already suffering from poor high-altitude performance, was no match for the Mustang at the B-17's altitude, and when laden with heavy bomber-hunting weapons as a replacement for the more vulnerable twin-engined Zerstörer heavy fighters, it suffered badly. The Messerschmitt Bf 109G was on a more even footing at high altitudes, but this lightweight platform was even more greatly affected by increases in armament. The Mustang's much lighter armament, tuned for anti-fighter combat, allowed them to hunt down both of these fighters with relative ease.

The Luftwaffe initially adapted to the U.S. fighters by modifying their tactics. Instead of approaching in small groups in ad-hoc formations, they instead formed up en masse in front of the bomber's line of approach, and then attacked by making a single pass through the formation. Flying in close formation with the bombers, the P-51s had little time to react before the attackers were already running out of range.

General James Doolittle told the fighters in early 1944 to stop flying in formation with the bombers and instead attack the Luftwaffe wherever it could be found. The Mustang groups were sent in well before the bombers in a "fighter sweep" as a form of air supremacy action, intercepting German fighters while they were forming up. As a result the Luftwaffe lost 17% of its fighter pilots in just over a week, and the Allies were able to establish air superiority. As Doolittle later noted, "Adolf Galland said that the day we took our fighters off the bombers and put them against the German fighters, that is, went from defensive to offensive, Germany lost the air war."

The Luftwaffe's answer was the Gefechtsverband (battle formation). It consisted of a Sturmgruppe of heavily armed and armored Fw 190As escorted by two Begleitgruppen of light fighters, often Bf 109Gs, whose task was to keep the Mustangs away from the Sturmböcke Fw 190As attacking the bombers. This scheme was excellent in theory but difficult to apply in practice as the large German formation took a long time to assemble and was difficult to maneuver. It was often intercepted by the escorting P-51s using the newer "fighter sweep" tactics out ahead of the heavy bomber formations, breaking up the Gefechtsverband formations before reaching the bombers; when the Sturmgruppe was able to work as intended, the effects were devastating. With their engines and cockpits heavily armored, the Fw 190As attacked from astern and gun camera films show that these attacks were often pressed to within 100 yds (90 m).

While not always able to avoid contact with the escorts, the threat of mass attacks and later the "company front" (eight abreast) assaults by armored Sturmgruppe Fw 190s brought an urgency to attacking the Luftwaffe wherever it could be found, either in the air or on the ground. Beginning in late February 1944, 8th Air Force fighter units began systematic strafing attacks on German airfields with increasing frequency and intensity throughout the spring with the objective of gaining air supremacy over the Normandy battlefield. In general these were conducted by units returning from escort missions but, beginning in March, many groups also were assigned airfield attacks instead of bomber support. The P-51, particularly with the advent of the K-14 Gyro gunsight and the development of "Clobber Colleges" for the training of fighter pilots in fall 1944, was a decisive element in Allied countermeasures against the Jagdverbände.

The numerical superiority of the USAAF fighters, superb flying characteristics of the P-51, and pilot proficiency helped cripple the Luftwaffe's fighter force. As a result the fighter threat to US, and later British, bombers was greatly diminished by July 1944. The RAF, long proponents of night bombing for protection, were able to re-open daylight bombing in 1944 as a result of the destruction of the Luftwaffe. Reichmarshal Hermann Göring, commander of the German Luftwaffe during the war, was quoted as saying, "When I saw Mustangs over Berlin, I knew the jig was up."

On 15 April 1944, VIII FC began Operation Jackpot, attacks on Luftwaffe fighter airfields. As the efficacy of these missions increased, the number of fighters at the German airbases fell to the point where they were no longer useful targets. On 21 May, targets were expanded to include railways, locomotives and rolling stock used by the Germans to transport materiel and troops, in missions dubbed "Chattanooga". The P-51 excelled at this mission, although losses were much higher on strafing missions than in air-to-air combat, partially because, like other fighters using liquid-cooled engines, the Mustang's coolant system could be punctured by small arms, unlike the air-cooled Double Wasp radials of its Republic P-47 stablemates based in England, regularly tasked with ground strafing missions.

Given the overwhelming Allied air superiority, the Luftwaffe put its effort into the development of aircraft of such high performance that they could operate with impunity. Foremost among these were the Messerschmitt Me 163 rocket interceptors and Messerschmitt Me 262 jet fighter. In action, the Me 163 proved to be more dangerous to the Luftwaffe than to the Allies and was never a serious threat. The Me 262 was a serious threat, but attacks on their airfields neutralized them. The jet engines of the Me 262s needed careful nursing by their pilots and these aircraft were particularly vulnerable during takeoff and landing. Lt. Chuck Yeager of the 357th Fighter Group was one of the first American pilots to shoot down an Me 262, which he caught during its landing approach. On 7 October 1944, Lt. Urban Drew of the 365th Fighter Group shot down two Me 262s that were taking off, while on the same day Lt. Col. Hubert Zemke, who had transferred to the Mustang equipped 479th Fighter Group, shot down what he thought was a Bf 109, only to have his gun camera film reveal that it may have been an Me 262.

The Mustang also proved useful against the V-1s launched toward London. P-51B/Cs using 150 octane fuel were fast enough to catch the V-1 and operated in concert with shorter-range aircraft like advanced marks of the Supermarine Spitfire and Hawker Tempest.

By 8 May 1945, the 8th, 9th and 15th Air Force's P-51 groups claimed some 4,950 aircraft shot down (about half of all USAAF claims in the European theater, the most claimed by any Allied fighter in air-to-air combat) and 4,131 destroyed on the ground. Losses were about 2,520 aircraft. The 8th Air Force's 4th Fighter Group was the top-scoring fighter group in Europe, with 1,016 enemy aircraft claimed destroyed. This included 550 claimed in aerial combat and 466 on the ground.

In air combat, the top-scoring P-51 units (both of which exclusively flew Mustangs) were the 357th Fighter Group of the 8th Air Force with 565 air-to-air combat victories and the Ninth Air Force's 354th Fighter Group with 664, which made it one of the top scoring fighter groups. Martin Bowman reports that in the European Theater of Operations, Mustangs flew 213,873 sorties and lost 2,520 aircraft to all causes. The top Mustang ace was the USAAF's George Preddy, whose final tally stood at 26 and a third, 23 of which were scored with the P-51, when he was shot down and killed by friendly fire on Christmas Day 1944 during the Battle of the Bulge.