Chanute Air Museum

In 1939, shortly after World War II began, the British government established a purchasing commission in the United States. At the time the choice was very limited: none of the U.S. aircraft already flying met European standards; only the Curtiss Tomahawk came close. The Curtiss plant was running at capacity, so even that aircraft was in short supply.

The North American Aviation P-51 Mustang was a long-range single-seat fighter aircraft that entered service with Allied air forces in the middle years of World War II.

The P-51 flew most of its wartime missions as a bomber escort in raids over Germany, helping ensure Allied air superiority from early 1944. It also saw limited service against the Japanese in the Pacific War. The Mustang began the Korean War as the United Nations' main fighter, but was relegated to a ground attack role when superseded by jet fighters early in the conflict. Nevertheless, it remained in service with some air forces until the early 1980s.

As well as being economical to produce, the Mustang was a fast, well-made, and highly durable aircraft. The definitive version, the P-51D, was powered by the Packard V-1650-7, a two-stage two-speed supercharged 12-cylinder Packard-built version of the legendary Rolls-Royce Merlin engine, and was armed with six .50 caliber (12.7 mm) Browning M2/AN machine guns, a version of the Browning adapted for use in combat aircraft.

While the United States Army Air Corps could block any sales it considered detrimental or not in the interest of the United States, the NA-73 represented a special case. In order to ensure deliveries were uninterrupted, an arrangement was eventually reached where the RAF would get its aircraft in exchange for NAA providing two free examples to the USAAC for evaluation.

The prototype NA-73X was rolled out just 117 days after the order was placed, and first flew on 26 October 1940, just 178 days after the order had been placed — an incredibly short gestation period. In general the prototype handled well and the internal arrangement allowed for an impressive fuel load. It was armed with four .30 caliber Browning (7.62 mm) and two .50 M2 Browning (12.7 mm) machine guns in the wings and two .50 M2s in the chin.

It was quickly evident that performance, although exceptional up to 15,000 feet (4,600 m), was markedly reduced at higher altitudes. This deficiency was due largely to the single speed, single stage supercharger of the Allison V-1710 engine, where power diminished rapidly above the critical altitude rating. Prior to the Mustang project, the USAAC had Allison concentrate primarily on turbo chargers in concert with General Electric; these proved to be exceptional in the P-38 Lightning and other high-altitude aircraft, in particular, the Air Corp's four-engine bombers. Most of the other uses for the Allison were for low-altitude designs, where a simpler supercharger would suffice. The turbo charger proved impractical in the Mustang, and it was forced to use the inadequate supercharger available. Still, the Mustang's advanced aerodynamics showed to advantage, as the Mustang I was about 30 mph (48 km/h) faster than contemporary Curtiss P-40 fighters, using the same power plant (the V-1710-39 producing 1,220 hp (910 kW) at 10,500 ft (3,200 m), driving a 10-foot-6-inch (3.2 m) diameter, three-blade Curtiss-Electric propeller). The Mustang I was 30 mph (48 km/h) faster than the Spitfire Mk VC at 5,000 ft (1,500 m) and 35 mph (56 km/h) faster at 15,000 ft (4,600 m), despite the British aircraft's more powerful engine.

The first production contract was awarded by the British for 320 NA-73 fighters, named Mustang I by the British (the name being selected by an anonymous member of the Purchasing Commission). Two aircraft of this lot delivered to the USAAC for evaluation were designated XP-51. About 20 Mustang Is were delivered to the RAF, making their combat debut on 10 May 1942. With their long range and excellent low-level performance, they were employed effectively for tactical reconnaissance and ground-attack duties over the English Channel, but were thought to be of limited value as fighters due to their poor performance above 15,000 ft.

A second British contract called for 300 more (NA-83) Mustang I fighters. In September 1940, 150 aircraft, designated NA-91 by North American, were ordered under the Lend/Lease program. These were designated by the USAAF as P-51 and initially named Apache, although this was soon dropped and the RAF name, Mustang, adopted instead. The British designated this model as Mustang IA. The Mustang Mk IA was identical to the Mustang Mk I except that the wing mounted machine guns were removed and replaced with four long-barreled 20 mm Hispano Mk II cannon.

A number of aircraft from this lot were fitted out by the USAAF as F-6A photo-reconnaissance aircraft. The British would fit a number of Mustang Is with similar equipment. Also, two aircraft of this lot were fitted with Packard-built Merlin engines. These were identified as the Model NA-101 by North American and XP-78 by the USAAF, later redesignated XP-51B.

In early 1942, the USAAF ordered 500 aircraft modified as dive bombers that were designated A-36A (NA-97). This model became the first USAAF Mustang to see combat. One aircraft was passed to the British who gave it the name Mustang I (Dive Bomber).

In April 1942, the RAF's Air Fighting Development Unit (AFDU) tested the Mustang and found its performance inadequate at higher altitudes. As such it was to be used to replace the Tomahawk in Army Cooperation Command squadrons. Rolls-Royce engineers rapidly realized that equipping the Mustang with a Merlin 61 engine with its two speed, two stage supercharger would substantially improve performance and started converting five aircraft as the Mustang X. Apart from the engine installation, which utilized custom built engine bearers designed by Rolls-Royce and a standard 10 ft 9 in diameter, four bladed Rotol propeller from a Spitfire Mk. IX the Mustang X was a straight-forward adaptation of the Mustang I airframe, keeping the same radiator duct design.

The high-altitude performance improvement was astonishing: the Mustang X (AM208) reached 433 mph at 22,000 ft and AL975 tested at an absolute ceiling of 40,600 ft.
It was decided that the armament of the new, P-51B (NA 102) would be the four .50 Cal Browning M2/AN machine guns (with 350 rpg for the inboard guns and 280 rpg for the outboard) of the P-51A and the bomb rack/external drop tank installation (adapted from the A-36) would also be used; the racks were rated to be able to carry up to 500 lb (230 kg) of ordnance and were also capable of carrying drop tanks. The weapons were aimed using an N-3B optical gunsight fitted with an A-1 head assembly which allowed it to be used as a gun or bomb sight through varying the angle of the reflector glass.

The first XP-51Bs started test flying in December 1942. After sustained lobbying at the highest level, American production was started in early 1943 with the B (NA-102) being manufactured at Inglewood, California, and the C (NA-103) at a new plant in Dallas, Texas, which was in operation by summer 1943. The RAF named these models Mustang III. In performance tests, the P-51B reached 441 mph (exactly two-thirds supersonic speed at altitude) at 25,000 f and the subsequent extended range made possible by the use of drop tanks enabled the Merlin-powered Mustang to be introduced as a bomber escort.

Despite these modifications the P-51 Bs and Cs and the newer Ds and Ks experienced low speed handling problems that could result in an involuntary "snap-roll" under certain conditions of air speed, angle of attack, gross weight and center of gravity. Several crash reports tell of P-51Bs and Cs crashing because horizontal stabilizers were torn off during maneuvering. As a result of these problems a modification kit consisting of a dorsal fin was manufactured.

These kits became available in August 1944 and were fitted to Bs and Cs and to Ds and Ks. Also incorporated was a change to the rudder trim tabs, which would help prevent the pilot over-controlling the aircraft and creating heavy loads on the tail unit.

P-51Bs and Cs started to arrive in England in August and October 1943. The P-51B/C versions were sent to 15 fighter groups that were part of the 8th and 9th Air Forces in England, and the 12th and 15th in Italy (the southern part of Italy was under Allied control by late 1943). Other deployments included the China Burma India Theater (CBI).

Allied strategists quickly exploited the long-range fighter as a bomber escort. It was largely due to the P-51 that daylight bombing raids deep into German territory became possible without prohibitive bomber losses in late 1943.

Luftwaffe pilots attempted to avoid U.S. fighters by massing in huge numbers well in front of the bombers, attacking in a single pass, then breaking off the attack, allowing escorting fighters little time to react. While not always successful in avoiding contact with the escort (as the tremendous loss of German pilots in the spring of 1944 indicates), 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. The P-51, particularly with the advent of the K-14 gunsight and the development of "Clobber Colleges" for the in-theater training of fighter pilots in fall 1944, was a decisive element in Allied countermeasures against the Jagdverbände.

Beginning in late February 1944, Eighth Air Force fighter units began systematic strafing attacks on German airfields that picked up in 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. On 15 April, VIII FC began Operation Jackpot, attacks on specific Luftwaffe fighter airfields, and on 21 May, these attacks 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 also 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 hits, even from a single bullet.

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 summer 1944.

Among other modifications, armament was increased with the addition of two M2 machine guns, bringing the total to six. The inner pair of machine guns had 400 rounds each, and the others had 270 rounds, for a total of 1,880. In previous P-51s, the M2s were mounted at an extreme side angle to allow access to the feed chutes from the ammunition trays. This angled mounting had caused problems of congestion and jamming of the ammunition and spent casings and links, leading to frequent complaints of jamming during combat maneuvers. The new arrangement allowed the M2s to be mounted upright, remedying most of the jamming problems. The .50 caliber Browning machine guns, although not firing an explosive projectile, had excellent ballistics and proved adequate against the Fw 190 and Bf 109 fighters that were the main USAAF opponents at the time. The wing racks fitted to the P-51D/K series were strengthened and were able to carry up to 1,000 lb of ordnance. Later models had under-wing rocket pylons added to carry up to ten rockets per plane.

The P-51D started arriving in Europe in mid-1944 and quickly became the primary USAAF fighter in the theater. It was produced in larger numbers than any other Mustang variant. Nevertheless, by the end of the war, roughly half of all operational Mustangs were still B or C models.

The P-51H was the final production Mustang, embodying the experience gained in the development of the XP-51F and XP-51G aircraft. This aircraft, with minor differences as the NA-129, came too late to participate in World War II, but it brought the development of the Mustang to a peak as one of the fastest production piston engine fighters to see service.

The P-51H used the new V-1650-9 engine, a version of the Merlin that included Simmons automatic supercharger boost control with water injection, allowing War Emergency Power as high as 2218 hp Differences between the P-51D included lengthening the fuselage and increasing the height of the tailfin, which greatly reduced the tendency to yaw. The canopy resembled the P-51D style, over a somewhat raised pilot's position. Service access to the guns and ammunition was also improved. With the new airframe several hundred pounds lighter, the extra power and a more streamlined radiator, the P-51H was among the fastest propeller fighters ever, able to reach 487 mph at 25,000 ft..

The P-51H was designed to complement the P-47N as the primary aircraft for the invasion of Japan with 2,000 ordered to be manufactured at Inglewood. Production was just ramping up with 555 delivered when the war ended. Additional orders, already on the books, were cancelled. With the cutback in production, the variants of the P-51H with different versions of the Merlin engine were produced in either limited numbers or terminated.

The Eighth, Ninth and Fifteenth Air Forces' P-51 groups, all but three of which flew another type before converting to the Mustang, claimed some 4,950 aircraft shot down (about half of all USAAF claims in the European theater) and 4,131 destroyed on the ground. Losses were about 2520 aircraft.

One of these groups, the Eighth Air Force's 4th Fighter Group, was the overall 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 aerial combat, the top-scoring P-51 units (both of which exclusively flew Mustangs) were the 357th Fighter Group of the Eighth Air Force with 595 air-to-air combat victories, and the Ninth Air Force's 354th Fighter Group with 701, which made it the top scoring outfit in aerial combat of all fighter groups of any type. Martin Bowman reports that in the European Theater of Operations, Mustangs flew 213,873 sorties and lost 2,520 aircraft to all causes.

In the aftermath of World War II, the USAAF consolidated much of its wartime combat force and selected the P-51 as a "standard" piston engine fighter while other types such as the P-38 and P-47 were withdrawn or given substantially reduced roles. However, as more advanced jet fighters (P-80 and P-84) were being introduced, the P-51 was relegated to secondary status.

In 1947, the newly-formed USAF Strategic Air Command employed Mustangs alongside F-6 Mustangs and F-82 Twin Mustangs, due to their range capabilities. In 1948, the designation P-51 (P for pursuit) was changed to F-51 (F for fighter) and the existing F designator for photographic reconnaissance aircraft was dropped because of a new designation scheme throughout the USAF.

At the start of the Korean War, the Mustang once again proved its usefulness. With the availability of F-51Ds in service and in storage, a substantial number were shipped via aircraft carriers to the combat zone for use initially by both the Republic of Korea Air Force (ROKAF) and USAF. Rather than employing them as interceptors or "pure" fighters, the F-51 was given the task of ground attack, fitted with rockets and bombs. After the initial invasion from North Korea, USAF units were forced to fly from bases in Japan, and F-51Ds could hit targets in Korea that short-ranged F-80 jet fighters could not. A major concern over the vulnerability of the cooling system was realized in heavy losses due to ground fire. Mustangs continued flying with USAF and Republic of Korea Air Force (ROKAF) fighter-bomber units on close support and interdiction missions in Korea until they were largely replaced by Republic F-84 and Grumman Panther jet fighter-bombers in 1953. No. 77 Squadron Royal Australian Air Force (RAAF) operated Australian-built Mustangs as part of British Commonwealth Forces Korea, replacing them with Gloster Meteor F8s in 1951. No. 2 Squadron South African Air Force (SAAF) operated US-built Mustangs as part of the US 18th Fighter Bomber Wing, suffering heavy losses by 1953, when it converted to the F-86 Sabre.