North American P-51

North American P-51

By Joe Baugher


The fourth and tenth NA-73s were duly delivered to the Army in May 1941 for testing at Wright Field, designated XP-51 [41-038/039], initially unpainted except for national insignia and a black anti-glare panel ahead of the cockpit. The Army painted the serials 1038 and 1039 on the fin and on each side of the nose, together with the WRIGHT arrowhead logo on the rear fuselage. Much later, they were both painted overall olive drab.

    Testing of the two was rather slow at first, almost as if the Army didn't really want to bother with these airplanes and that they were some sort of nuisance. Some authors have suggested that there were dark and evil motives behind the Army's reluctance to test the ships; however, the slow pace can probably be blamed more on bureaucratic inertia than on anything all that sinister.

    At that time, Wright Field was overloaded with test programs, with the Lockheed's P-38 Lightning, Bell's P-39 Airacobra, and Republic's P-47 Thunderbolt being thought to meet all the Army's requirements for fighter aircraft. Nevertheless, once testing of the XP-51s did get under way, the Army's test pilots reported very favorably on their performances.

    Despite high scores in the tests, strangely no Army orders were forthcoming. Much later, a Senate Special Committee to Investigate the National Defense Program (the "Truman Committee") looked into the system under which military production contracts were awarded during wartime conditions. They sought specifically for the reason why the Army had sat on its hands for so long before ordering any examples of the P-51, an airplane with demonstrably superior performance.

    Some insiders claimed that NAA President "Dutch" Kindelberger had been asked to pay bribes in exchange for a production contract, and that he had refused all such demands in no uncertain terms. The primary cause of the Army's stall is likely somewhat less sinister. The Mustang could have been the victim of the "Not Invented Here" (NIH) syndrome, in which the Army looked askance at an upstart aircraft that had not been designed in response to any of its official requirements or specifications, and was therefore way down on their list of priorities.

A-36 Apache, Invader, Mustang

Only after Pearl Harbor did the Army finally agree to order the Mustang for its own use. General H H "Hap" Arnold, Chief of Staff of the USAAF, was instrumental in breaking up the bureaucratic log-jam and getting the Army to order the Mustang for its own use. On Apr 16, 1942 the Army finally ordered 500 NA-97s, a ground attack version designated A-36A (in the Attack rather than Fighter series) [42-83663/84162].

    The A-36 seems to have been known by several different names—it was initially called Apache, which was the AAC name initially assigned to the P-51, but there was an effort to change the name to Invader. However, the name Mustang was generally applied by most people to the A-36.

    The A-36A differed from previous Mustang versions in having a set of hydraulically-operated perforated door-type dive brakes mounted at approximately mid-chord on both the upper and lower wing surfaces outboard of the wing guns. The brakes were normally recessed into the wings, but were opened to 90&37; by a hydraulic jack to hold diving speeds down to 250 mph. A rack was fitted under each wing for a 500# bombs, a 75-gallon drop tank, or smoke-curtain equipment. It carried six .50 machine guns (two in lower fuselage nose, four in wings); however, the two nose guns were often omitted in service. Wing guns were closer to the main landing gear strut in order to minimize stress during taxi and take-off. Engine was the 1325hp Allison V-1710-87 (F21R). With the bombs, range and service ceiling were 550 miles and 25,100'.

The first A-36A flew on Sep 21, 1942 and deliveries were completed by the following March to the 27th and 86th Fighter Bomber Groups (FBG) based in Sicily and Italy. They initially were painted in olive-drab and light-gray finish with yellow wing bands and yellow circles around the national insignia. Both Groups arrived in North Africa in Apr 1943 just after the end of the Tunisian campaign. They saw their first action during aerial attacks on the island of Pantelleria, with the first sortie being flown on June 6, 1943. The A-36A was involved in the taking of Monte Cassino and participated in the sinking of the Italian liner Conte di Savoia. The only other A-36 user was the 311th FBG based in India and saw extensive use in the CBI theatre

    Several sources list the Invader as not being particularly effective during combat, but this is not entirely correct. Although losses during low-level attacks were rather high, the A-36 was actually a good dive-bomber and a stable and effective ground strafer. The engine was very quiet, so it was often possible for an A-36 to get on top of an enemy before they realized it. Dive-bombing was usually initiated from an altitude of 10,000-12,000', with speed held at around 300 by the dive brakes. Bombs were released at 3000', and pullout was at 1500 feet'.

    The Invader was fairly rugged and easy to maintain in the field. It could consistently fly at 20' of the deck and easily maneuver around trees and other obstacles while strafing, it was able to take a considerable amount of battle damage and still return to base. Still 177 A-36As were lost in action. One A-36A went to the RAF in March 1943 for unstated experimental purposes [EW998].

The A-36 did not see much air-to-air combat since it was optimized for low-altitude operations and lost its effectiveness above 10,000'. It was generally believed that an A-36 Invader was no match for a Messerschmitt Bf.109 at high altitudes, and that it was therefore best for A-36 pilots to avoid such encounters or, if combat was unavoidable, to force the battle down to altitudes below 8000', where advantage could be taken of the A-36A's excellent low-altitude performance. Although not a fighter, the Invader claimed 101 enemy aircraft destroyed in aerial combat. One pilot of the 27th FBG, Lt Michael Russo, became the only ace in the Allison-powered Mustang, although several other of his colleagues scored victories, as well.

    Folklore sprung up about the A-36A's dive brakes. For one, that the A-36A's brakes were next to useless and were deliberately wired shut at the manufacturers so that they could not be used—that story was pure fiction. On the contrary, they proved to be quite effective in combat, and the aircraft was so stable with them opened that dive-bombing was notably accurate throughout the Sicilian campaign and the Italian invasion.

F-6A (P-51) Mustang

The British did not get all of these NA-91s. Since RAF deliveries took place after Pearl Harbor, many were repossessed by the USAAC before they reached England, including RAF Mustang IAs [FD418/FD437, FD450/FD464, FD466/FD469, FD510/FD527]. Army P-51s were armed with four .50 machine guns rather than the 20mm cannon and were fitted with two K-24 cameras in the fuselage. Most retained their RAF camouflage and serial numbers, although some were indeed painted with their equivalent AAF s/ns. Those were designated as tactical reconnaissance aircraft and were designated F-6A, but that designation soon changed to P-51.

    The F-6As went to Peterson Field in Colorado where they were assigned to the newly-established aerial recon school. In Mar 1943 a batch of 25 F-6As were assigned to the 154th Observation Sqdn at Oujda in French Morocco as the first US Mustang unit. Their first mission there was a photo coverage of Kairouan airfield in Tunisia on Apr 10, 1943, which was also the first AAF Mustang mission of WW2. RAF 225 Sqdn frequently borrowed Mustangs from the 154th to augment its shorter-range Spitfires. The F-6A was quite successful in operation, but it did have one important defect—its shape was similar to that of the Bf.109. The 154th's first combat loss was from friendly in which Allied anti-aircraft teams failed to recognize the differences, with fatal results.

    Two F-6A/P-51 airframes were diverted to the XP-78 project, about which more will be said.

P-51A Mustang

The next Army contract for Mustangs consisted of an order on Aug 24, 1942 for 1,200 NA-99 versions as P-51A. The first P-51A flew on Feb 3, 1943 and first deliveries began the next month. Only 310 P-51As were actually built between March and May in 1943 before production was switched over to the Merlin-powered P-51B. When production of the Allisond Mustangs ended, 1,580 examples had been built.

    These aircraft had the same external stores capability as the A-36A Invader, but had no dive brakes or fuselage guns, armament being limited to four .50 machine guns in the wings. The inboard pair had 350 rpg and the outboard pair had 280 rpg. An underwing load consisted of two 250#, 325#, or 500# bombs. Maximum take-off weight rose to 10,600#, with maximum ferry range at 2350 miles. The P-51A had the 1200hp Allison V-1710-81 (F20R), with significantly better high-altitude performance than the V-1710-39, with a new supercharger that further enhanced low-altitude performance. In addition a larger-diameter propeller was fitted. Maximum airspeed rose to 409 mph at 11,000 feet, faster at medium altitudes than any other fighter then in service.

    Because of the thin wing cross-section, wing guns lay almost on their sides and ammo belt feeds had to be built with some rather sharp kinks in them in order to feed the bullets. This awkward arrangement resulted in many gun jams, particularly after high-G maneuvers.

Fifty P-51As went to the RAF late in 1942 as Mustang IIs (they replaced the NA-91s that had been diverted from Mustang IA orders for conversion as AAF F-6As) [FR890/FR939]. [FR901] was fitted with special deep-section fuel tanks beneath the wings for ultra-long-range flying.[FR893] was tested and demonstrated a best rate-of-climb of 3800 fpm with an altitude of 20,000' reached in 6.9 minutes and 34,000 feet in 24 minutes. Mustang I, IA, and II had impressively long service with the RAF, with the last front-line RAF Allison-powered ships being phased out in early 1945.

    The first P-51A group was the 54th, which remained in Florida for replacement training. Later, P-51As went to Asia with the 23rd, 311th, and 1st Air Commando Groups—most all P-51As served in the CBI theatre. On Nov 25, 1943 the 530th Sqdn of the 311th FBG flew the first of the Mustang's long-range escort missions, using drop tanks to escort B-24 Liberators in an attack on Rangoon, a round trip of nearly 900 miles. F-6Bs did serve in Europe, mainly with the 107th Tactical Recon Sqdn based in England. Of the 310 P-51As built, 35 had guns removed, were fitted with twin-K24 cameras, and were redesignated F-6B. One P-51A went to USN for evaluation [57987]

    POP: 100 P-51A-1-NA [43-6003/6102], 55 P-51A-5-NA [43-6103/6157] , 155 P-51A-10-NA[43-6158/6312].

Mustang X

On April 30, 1942 Ronald W Harker, a test pilot for Rolls-Royce, took a brief hop in a RAF Mustang and was highly impressed with it as faster than the Spitfire VB at similar power settings and with nearly twice the range. He reported the plane as a natural for the new Merlin 60 that Rolls-Royce was just beginning to produce for the Spitfire VIII.

    Management was intrigued by the idea and requested three Mustangs to test with Merlins. Various Merlins were studied, including the single-stage Mk XX and the two-stage Mk 61—the two-stage Merlin was the better choice because of its superior high-altitude performance. Its crankshaft was geared to two supercharger blowers stacked in series. Because of rapid compression, temperature of the air after it passed through both stages increased by 200° C. To lower this temperature and thus increase the air mass flow to the engine, an intercooler was added, requiring an extra radiator underneath the nose, in the same duct as the ram inlet for the updraft carburetor.

    Initially, three Mustang Is were allocated to the program on Aug 12, 1942 and two more later [AL963, AL975, AM121, AM203, AM208]. As Mustang X, no two were exactly alike, but all had small chin-type radiators under the engine and four-bladed props to absorb the extra power of a Merlin 65, which in comparison with the Merlin 66 had a lower full-throttle height but gave higher power at lower altitudes. Compared the Allison V-1710, it was 205hp more powerful at 20,000'and 490hp more powerful at 25,000'.

    The first Mustang X [AL975] took wing on Oct 12, 1942, piloted by Capt R T Shepherd, [AL963] followed on Nov 13, with [AM121] on Dec 13 going to Duxford for service evaluation. The remaining two were evaluated by the AAF in US markings. The Mustang Xs were busy the rest of the war testing various later marks of the Merlin engine.

The performance of those aircraft was excellent, with speeds of 433 mph at 22,000'; however, yaw stability was degraded by the increased side area of the nose. But success of the tests led Rolls-Royce to propose production of 500 Merlin 65s to bring most of the RAF's Mustang fleet up to Mark X standards, but there was no place where such conversions could be done and plans were dropped.

    A bizarre proposal by Rolls-Royce was a test installation of a 2400hp Griffon 63 in a Mustang mounted amidships, like P-39 Airacobra, driving a contrarotating prop via an extension shaft and a cockpit moved forward well ahead of the wing. It was anticipated that te modification would make possible speeds up to 500 mph. A mockup was prepared, but the concept was abandoned.

XP-51B, XP-78

Rolls-Royce had informed US military attache Maj Thomas Hitchcock in May 1942 of their plans to convert Mustangs to the Merlin engine. Coincidentally Hitchcock had been thinking of that idea, too, and he passed the word along to Wright Field and NAA. It so happened that at the time negotiations were taking place with the Packard Motor Car Co Michigan for license manufacture in the US of the new Merlin engine with the two-stage supercharger. On July 25 NAA was authorized to convert two Mustangs to Merlin 65s ifrom England. The aircraft were considered sufficiently different from the existing Mustang to warrant a new designation, XP-78.

    NAA selected two P-51s from the batch of RAF Mustang IAs repossessed by AAF [41-37350] and [41-37421] and gave the project company designation NA-101. That designation was changed to XP-51B while work progressed. Although the early work of Rolls-Royce of Mustangs and Merlins provided valuable insight to North American engineers, the British manufacturer did not directly participate in the project any further.

    Carburetor air intake was moved to below the nose in order to accommodate the Merlin's updraft induction system. The intercooler radiator was added to the radiator group already located inside the scoop under the rear fuselage, and the ventral radiator group was made noticeably deeper than before and had a sharp-angled inlet standing more than two inches away from the underside of the fuselage. Instead of the oil cooler being situated in the center of a circular coolant radiator, it was relocated to the front of the duct and provided with its own ventral exit door. Further downstream, in a greatly enlarged duct, was the huge rectangular coolant matrix with a much bigger exit door at the rear.

    Airframes were strengthened to make full use of the increased power available. New ailerons were fitted and the underwing racks were increased in capacity to take two 1000# bombs or their equivalent weight in drop tanks. A new four-blade Hamilton Standard hydromatic paddle-blade propeller was fitted. Fuselage-mounted guns were eliminated in favor of four 0.50s exclusively in the wings.

    The first XP-51B was flown by Bob Chilton on Nov 30, 1942, initially without armament. Performance improvement was nothing short of astounding—a level speed of 441 mph at 29,800' was more than 100 mph faster than the Allison P-51 at that altitude, and at all heights the rate of climb about doubled!

P-51B/C (F-6B/C) Mustang

Even before the first example had flown, 400 P-51Bs were ordered in Aug 1942 based on NAA's performance estimates. The USAAF finally had an aircraft which could compete on equal terms with the Fw.190 and later Bf.109, and a contract was issued for 2,200 P-51Bs with the Packard V-1650-3 that was based on the Merlin 68.

    In late 1942 a deal between Britain and the USA was made in which Spitfire VBs would be transferred to the 8th AF in England, mainly for use as fighter-trainers. This cleared the way for Lend-Lease supplies with the USAAF P-51B/C as Mustang III. The RAF ultimately received 274 P-51Bs and 626 P-51Cs, and 59 Mustang IIIs were diverted to the Royal Australian AF and other Allied air arms.

    As 1943 dawned, the Mustang program suddenly expanded. Massive production of Merlin engines was to take place at both Packard at Detroit and Continental at Muskegon IL. The huge Inglewood factory was expanded and dedicated solely to P-51 production, with the B-25 program transferred to Kansas City. Production of AT-6 trainers had earlier been transferred from Inglewood to a new plant built in great haste at Dallas TX. NAA even expand the Dallas plant further as a second source for Mustangs. Inglewood-built planes were designated P-51B, Dallas-built Mustangs were P-51C. The aircraft were almost identical and generally distinguished only by serial number.

    By the end of Jan 1943 production standard for the P-51B/C had been decided. To take full advantage of the additional power, the airframe was re-stressed in detail and the aircraft was made capable of operating at considerably greater weights than was previously possible. Wing racks were modified to carry bombs of 1000# each or a range of other stores, including drop tanks or triple rocket tubes.

    Engine installation was further refined with a rectangular filtered-air inlet added in each side of the carburetor duct, and the exhaust expelled through individual ejector stubs projecting through a slim fairing. Ailerons were modified aerodynamically and structurally, although the changes were visible externally only by the fact that the tabs were made of plastic. Armament was four .50 Browning MG53-2 guns in the wings, with 350 rounds for each inner gun and 280 rounds for each outer gun. Fuselage nose guns were deleted.

The first P-51B flew on May 5, 1943 and the first P-51C on Aug 5. Inglewood built 1,988 P-51Bs and Dallas built 1,750 P-51Cs. P-51Cs on the 1942-43 budgets were given the company designation NA-103—1,350 NA-103s were built. Texas-built aircraft in the 1944 budget were designated NA-111.

    Initially, the P-51B/C had the Packard V-1560-3 rated 1400hp for take-off and 1450hp at 19,800' and four machine guns with a total of 1260 rounds. 400 P-51B-1-NAs and 250 P-51C-1-NTs were produced.

    In the pursuit of still more range, a P-51B was experimentally fitted with an extra 85-gallon self-sealing fuel tank behind the pilot's seat, bringing the total fuel to 419 gallons, including 2 drop tanks. Although the Mustang already offered outstanding range performance, additional fuel made it even better. Extra range was being demanded by expanding operations in both the European and Pacific theatres.

    However, the extra fuel tank moved the center of gravity aft, which affected directional stability, and pilots had to concentrate on keeping planes pointed in the right direction until the tank was empty. The last 550 P-51B-5-NAs fitted with this extra tank became P-51B-7-NA, and P-51C-1-NTs became P-51C-3-NT. Some earlier P-51Bs and Cs were also modified in the field with that tank, but in service, because of the directional instability hazard for new or inexperienced pilots, the tank was restricted to 65 gallons. The extra tank still made a crucial difference in combat radius—Mustangs could escort bombers all the way to Berlin from British bases—and was standard equipment in all future production versions.

During P-51B/C production it was also decided to omit the olive drab camouflage and to deliver aircraft in their natural metal finish. The objective was not only to save extra cost, weight, and drag, but to try and coax the Luftwaffe into battle, not hide from it.

    With the introduction of the P-51C-5-NT onto the Dallas production line and the P-51B-15-NA in the Inglewood line, the Packard V-1560-7 became standard. It offered 1450hp for take-off and a war-emergency rating of 1695hp at 10,300'. Max speed at 20,000' was reduced from 440 to 435 mph, but increased from 430 to 439 mph at 25,000'. 398 P-51B-10-NAs, 390 P-51B-15-NAs, and 1,350 P-51C-10-NTs thus powered were built.

    A total of 91 aircraft from the Block-10 production lot (71 P-51B-10-NAs and 20 P-51C-10-NTs) were fitted with two oblique K24 cameras, or a K17 and a K22, to become F-6C-NA or -NT photo aircraft, but most kept their guns. In each case cameras were mounted immediately in front of the structural break ahead of the tailwheel, looking out the left side.

    One problem encountered with the P-51B/C was the poor view from the cockpit, particular towards the rear. The Malcolm hood fitted to the P-51B/C was an early attempt to correct that deficiency. Two P-51B-10-NAs [42-106539/106540] were completed on the production line as XP-51Ds to test its validity.

The first combat unit equipped with Merlin-powered Mustangs was the 354th Fighter Group (FG), which reached England in Oct 1943. The 354th consisted of the 353rd, 355th and 356th Fighter Sqdns and was part of the 9th AF, which had the responsibility of air-to-ground attacks in support of the upcoming invasion. However, they were instead ordered to support bomber operations of the 8th AF. The 354th flew their first cross-Channel sweep mission on Dec 1, 1943 and scored a first victory Dec 16 during a Bremen mission. However, inexperienced pilots and ground crews and numerous technical problems limited operations with the P-51B/C until about eight weeks into 1944, when from early spring of that year the Merlin Mustang became an important fighter in the ETO.

    The first P-51 ace was Maj James H Howard of the 354th who. on Jan 11, 1944, shot down five German fighters to become an "ace-in-a-day" and earned the Medal of Honor for his feat. The 357th also flew its first escort mission on Feb 11, 1944.

The 15th AF was formed in Nov 1943 with three P-38 groups based in the Mediterranean theatre to escort Allied bombers. During April 1944 Merlin Mustangs began replacing Spitfires of the 31st and 52nd FGs, which transferred from the 12th to the 15th AF. The 31st flew its first mission on Apr 21, 1944 when its Mustangs escorted B-24s in an attacking Romanian oil refineries at Ploesti.

    The third fighter unit to join the 15th AF was the 332nd FG, manned entirely by Negro airmen trained at Tuskegee, the Army being a segregated service in those days. They transitioned to the P-51C in June 1944 while based at Foggia, Italy. Top scorer was Lt Lea Archer with 5 air and 6 ground victories, although one aerial victory was later reallocated to another pilot to prevent him from becoming an ace. The proudest record of the 332nd was that it never lost a bomber in its charge.

    In Mar 1944, Mustangs accompanied B-17s and B-24s all the way on a 1,100-mile Berlin round-trip. The ability of escort fighters to accompany bomber formations to their targets and still effectively counter Luftwaffe fighters after jettisoning drop tanks caused the German defenses no end of problems and added considerable impetus to the American daylight bombing offensive.

    Most P-51B/Cs were assigned to the 8th and 9th Air Forces in England, and a lesser number with the 12th or 15th in Italy. The P-51B/C remained the prime variant in service from Dec 1943 until Mar 1944, when the bubble-topped P-51D began to arrive. Yet P-51B/C fighters were predominant until the mid-1944 and remained in combat until the end of the war in Europe. Even as late as the last month of the war, 1.000 out of the 2.500 Mustangs serving in the ETO were P-51B/Cs. Although the P-51D was better known, the P-51B/C was actually the aircraft that turned the tide of the bomber war over Germany.

Merlin-powered Mustangs also entered service in the CBI theatre in Sep 1943, assigned to the 23rd and 51st FGs of the 5th AF. Early in 1944 the 311th FG of the 10th AF saw action in Burma with its Mustangs supporting airborne troops attacking Japanese lines of communication. The top Mustang ace of the CBI theatre was Maj John C "Pappy" Herbst, with 18 victories. About 100 P-51B/Cs were also supplied to the Chinese AF in 1943-44.

    In June 1944 the 10th Tactical Recon Group picked up the 12th and 15th Recon Sqdns equipped with F-6B and F-6C photo aircraft. F-6s served with the 8th, 9th, 12th, and 15th AFs, and with the 5th AF in the Far East. They retained their four .50 guns, and had frequent encounters with Luftwaffe fighters. Capt Clyde East of the 15th FS was the war's top-scoring recon pilot with 15 aerial victories. During late 1944 French units acquired some F-6Cs for over Germany in Jan 1945 photo-mapping missions.

    P-51B/Cs not only flew combat with front-line units until the end of hostilities, but were converted as two-seat trainers or squadron hacks. The last P-51B, re-designated F-51B in 1948, passed out of service in 1949.

    POP: 400 P-51B-1-NA [43-12093/12492], 800 P-51B-5-NA [43-6313/7112], 400 P-51B-10-NA [42-106429/106540, 106541/106738, 43-7113/7202], 390 P-51B-15-NA [42-106739/106978, 43-24752/24901].
    POP: 350 P-51C-1-NT [42-102979/103328], 450 P-51C-5-NT [42-103329/103778], 824 P-51C-10-NT [42-103779/103978, 43-24902/25251, 44-10753/10782, 10818/10852, 10859/11036, 11123/11152], 128 P-51C-11-NT[44-10783/10817, 10853/10858, 11037/11122].

Continue to XP-51D, P-51D, P-51K, XP-51F, XP-51G, XP-51J, P-51H, P-51M