P-51D Mustang

P-51D 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 in several other conflicts. During World War II Mustang pilots claimed 4,950 enemy aircraft shot down, second only to the Grumman F6F Hellcat.

It was conceived, designed and built by North American Aviation (NAA), under the direction of lead engineer Edgar Schmued, 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, albeit without an engine, 102 days after the contract was signed and it was first flown on 26 October. The Mustang was originally designed to use a low-altitude rated Allison V-1710 engine, and was first flown operationally by the Royal Air Force (RAF) as a tactical-reconnaissance aircraft and fighter bomber. The definitive version, the P-51D, was powered by the Packard V-1650-7, a licence-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.

At the start of Korean War the Mustang was the main fighter used by the United Nations. Jet fighters, including the F-86, took over this role, and the Mustang became a specialized ground attack 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.

Genesis

P-51 performing at a Virginia airshowIn 1939, shortly after World War II began, the British government established a purchasing commission in the United States, headed by Sir Henry Self. Along with Sir Wilfrid Freeman, who, as the “Air Member for Development and Production”, was given overall responsibility for RAF production and research and development in 1938. Self had sat on the (British) Air Council Sub-committee on Supply (or “Supply Committee”), and one of Self’s many tasks was to organize the manufacture of American fighter aircraft for the RAF. At the time the choice was very limited: none of the US aircraft already flying met European standards; only the Curtiss P-40 Tomahawk came close. The Curtiss plant was running at capacity, so even that aircraft was in short supply.

North American Aviation (NAA) was already supplying their Harvard trainer to the RAF, but were 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 licence from Curtiss.

Kindelberger replied that NAA could have a better aircraft with the same engine in the air in less time than it would take to set up a production line for the P-40. As executive head of the British Ministry of Aircraft Production (MAP), Freeman ordered 320 aircraft in March 1940. On 26 June 1940, MAP awarded a contract to Packard to build modified versions of the Rolls-Royce Merlin engines under licence;in September, MAP increased the first production order by 300.

Design and Development

The result of the MAP order was the NA-73X project (from March 1940). The design followed the best conventional practice of the era, but included two new features. One was a new NACA-designed laminar flow wing, which was associated with very low drag at high speeds. Another was the use of a new radiator design that used the heated air exiting the radiator as a form of jet thrust in what is referred to as the “Meredith Effect”. Because North American lacked a suitable wind tunnel, it was forced to use Curtiss’ facility. This led to some controversy over whether the Mustang’s aerodynamics were developed by North American’s engineer Edgar Schmued or by Curtiss, although historians and researchers dismiss the allegation of stolen technology; such claims are likely moot, in any event, as North American had purchased Curtiss’ complete set of P-40 and XP-46 wind tunnel data and flight test reports for $56,000.

The United States Army Air Corps could block any sales it considered interesting, and this appeared to be the case for the NA-73. An arrangement was eventually reached where the RAF would get its aircraft, in exchange for NA providing two examples cost-free to the USAAC.

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. 50 M2 Browning (12.7 mm) guns and two. 30 Browning (7.62 mm) guns. In comparison, the British Spitfire Vb carried two 20 mm cannon and four. 303 machine guns.

At the Casablanca Conference, the Allies formulated the Combined Bomber Offensive (CBO) plan for “round-the-clock” bombing by the RAF at night and the USAAF by day. American pre-war bombardment doctrine held that large formations of heavy bombers flying at high altitudes would be able to defend themselves against enemy interceptors with minimal fighter escort, so that precision daylight bombing using the Norden bombsight would be effective.

Both the RAF and Luftwaffe had attempted daylight bombing and discontinued it, believing advancements in single-engine fighters made multi-engined bombers too vulnerable, contrary to Douhet’s thesis. The RAF had worried about this in the mid-1930s and had decided to produce an all night-bomber force, but initially began bombing operations by day. The Germans used extensive daylight bombing during the Battle of Britain in preparation for a possible invasion. The Luftwaffe found daylight bombing raids sustained high casualties and soon switched to night bombing. Bomber Command followed suit in its subsequent raids over Germany.

Initial USAAF efforts were inconclusive because of the limited scale. In June 1943, the Combined Chiefs of Staff issued the Pointblank Directive to destroy the Luftwaffe before the invasion of Europe, putting the CBO into full implementation. The Eighth Air Force heavy bomber force conducted a series of deep penetration raids into Germany beyond the range of available escort fighters. German fighter reaction was fierce and bomber losses were severe — 20 percent in an October 14 attack on the German ball-bearing industry. This made it impossible to continue such long-range raids without adequate fighter escort.

The Lockheed P-38 Lightning had the range to escort the bombers, but was available in very limited numbers in the European theater due to its Allison engines proving difficult to maintain. With the extensive use of the P-38 in the Pacific Theater of Operations, where its twin engines were deemed vital to long-range “over-water” operations, nearly all European-based P-38 units converted to the P-51 in 1944. 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 Mustang changed all that. In general terms, the Mustang was at least as simple as other aircraft of its era. It used a single, well-understood, 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.

Ferry pilot Florene Watson, Women Airforce Service Pilots, warms up a P-51.Enough P-51s became available to the 8th and 9th Air Forces in the winter of 1943-44, and when the Pointblank offensive resumed in early 1944, matters changed dramatically. The P-51 proved perfect for the task of escorting bombers all the way to the deepest targets, thus complementing the more numerous P-47s until sufficient Mustangs became available. The Eighth Air Force immediately began to switch its fighter groups to the Mustang, first exchanging arriving P-47 groups for those of the Ninth Air Force using P-51s, then gradually converted its Thunderbolt and Lightning groups until by the end of the year 14 of its 15 groups flew the Mustang.

Luftwaffe pilots attempted to avoid US 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 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 April 15 VIII FC began Operation Jackpot, attacks on specific Luftwaffe fighter airfields, and on May 21 these attacks were expanded to include railways, locomotives, and rolling stock used by the Germans for movements of 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 due to the vulnerability of the Mustang’s cooling system to small arms hits. Like other fighters using liquid cooled engines, the Mustang’s coolant system could be punctured by a hit from a single bullet.

The numerical superiority of the USAAF fighters, superb flying characteristics of the P-51 and pilot proficiency crippled the Luftwaffe. As a result, the fighter threat to US, and later British bombers, was greatly diminished by summer 1944.P-51s also distinguished themselves against advanced enemy rockets and aircraft. A P-51B/C with high-octane fuel was fast enough to pursue the V-1s launched toward London. The Me 163 Komet rocket interceptors and Me 262 jet fighters were considerably faster than the P-51, but not invulnerable. Chuck Yeager, flying a P-51D, was one of the first American pilots to shoot down a Me 262 when he surprised it during its landing approach.

Chuck Yeager’s P-51D Glamorous Glennis III, is the aircraft in which the future test pilot achieved most of his 12.5 kills.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 840 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 destroyed, 550 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 ETO Mustangs flew 213,873 sorties and lost 2,520 aircraft to all causes.P-51s were deployed in the Far East later in 1944, operating in both close-support and escort missions.