The North American Aviation P-51 Mustang is 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 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, matching or bettering that of the Luftwaffe's fighters.[nb 1] The definitive version, the P-51D, was powered by the Packard V-1650-7, a license-builtversion 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 theaters, and saw limited service against the Japanese in the Pacific War. During World War II, Mustang pilots claimed 4,950 enemy aircraft shot down.[nb 2]
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.
Design and development
North American NA-73X; note the short carburetor air intake scoop and the frameless, rounded windscreen. On the production Mustang Mk Is the latter was replaced with a three-piece unit incorporating a bullet resistant windscreen
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 newmedium 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.[nb 3] 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 theUniversity of Washington Kirsten Wind Tunnel. The results of this test showed the superiority of the wing designed with the NAA/NACA 45–100 airfoils.[nb 4]
, one of two Mustang Mk Is handed over to the USAAC for testing
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.
The prototype NA-73X was rolled out in September 1940, just 102 days after the order had been placed; it first flew on 26 October 1940, 149 days into the contract, an uncommonly short gestation period even during the war. With test pilot Vance Breese at the controls) 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.[nb 5]
U.S. operational service
P-51D 374th Fighter Squadron. This is an early D-model, without the fin strake; 75 gallon (284-litre) drop tanks are on the wing racks.
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-flyingLockheed 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.
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 other paths; at first it was believed that the Boeing YB-40 would be able to escort the bomber formations, but, when the concept proved to be unsuccessful, thoughts then turned to the Lockheed P-38 Lightning. [nb 6] In early 1943 the USAAF also decided that theRepublic P-47 Thunderbolt and P-51B be considered for the role of a smaller escort fighter and, in July a report stated that the P-51B was "... the most promising plane ..." with an endurance of four hours 45 minutes with the standard internal fuel of 184 gallons plus 150 gallons carried externally. In August a P-51B was fitted with an extra internal 85 gallon tank and, although there were problems with longitudinal stability and some compromises in performance with the tank full, it was decided that because the fuel from the fuselage tank would be used during the initial stages of a mission, the fuel tank would be fitted in all Mustangs destined for VIII Fighter Command.