The North American Mustang was an aircraft type with two sides to its story. The widespread fame of Merlin-engined examples as high-altitude escort fighters has led to their Allison-engined predecessors being largely forgotten and often unjustly maligned. This viewpoint is completely wrong and ignores the facts behind the creation of the Mustang in the first place, when high-altitude heavy bomber escort work had not even been considered.
Despite Britain’s ongoing rearmament as war approached during 1939, the country was still short of many necessary components. RAF units were increasingly converting to the excellent Supermarine Spitfires and Hawker Hurricanes that would ultimately win the Battle of Britain in 1940. However, British requirements were many, and certainly more combat aircraft than were available from British factories were going to be needed then and in the following years.
With realistically nowhere else to turn, Britain looked to the neutral US as a potential source of additional military equipment. A new British buying organisation was formed in November 1939, and its members subsequently had a direct influence on the creation of the Mustang. This body was called the British Purchasing Commission (BPC; often incorrectly called the British Direct Purchasing Commission). Acquisitions subsequently comprised all manner of equipment for British service, not by any means confined to aircraft. At this time there was no ‘Lend-Lease’, so Britain paid for everything with hard currency. One of the aircraft designs that the BPC identified as a major warplane type for RAF operations was the Curtiss P-40 series, which was subsequently supplied in large numbers for British and Commonwealth service.
However, the P-40 was also a major production programme for the US Army Air Corps (USAAC) and the manufacturing facilities at the Curtiss plant were becoming stretched to full capacity.
The BPC contacted North American Aviation (NAA) of Inglewood, California, to licence-build P-40s for Britain. NAA was a comparatively new company, but its forward-looking management and designers were completely unimpressed with the idea of building someone else’s fighter. Instead, they proposed to the BPC that it would design and build its own, totally new warplane for British service.
In an unprecedented move, this offer was accepted and within a short time during early 1940, NAA’s designers had roughed out the basic layout of what became the Mustang. The most readily available engine to power the new design was the liquid-cooled Allison V-1710 V12, which was also the powerplant of the P-40. At that time there was no deal in place for the Rolls-Royce Merlin engine to be made in the US until much later in the war.
The inline V-1710 promised good medium- and low-level performance, which was ideal for the RAF at the time, with the Allison-powered P-40 series also acknowledged to perform best at those altitudes.
Rapid manufacture
The first example of NAA’s new design was ready for flight testing in a very short time. Known to the company as the NA-73, the prototype NA-73X received the US civil registration NX19998. The new airframe was company funded by NAA and, as such, had no military serial number assigned. It first flew at Mines Field (now Los Angeles International Airport) on October 26, 1940. At the controls was Vance Breese, a highly accomplished freelance test pilot.
It was clear straight away that the NA-73X was a superb performer: fast, manoeuvrable and with few obvious vices. The British authorities were well pleased with their new ‘pony’. Indeed, in May 1940, Britain had already signed up for 320 examples off the drawing board. Therefore the type was one of the few British warplanes that was not created to meet a formal official specification.
North American P-51A Mustang
Specifications
Powerplant 1 × Allison V-1710-81 liquid-cooled V12 inline engine, 1,200hp (895kW) for take-off
Crew 1
Length 32ft 2 7/8in (9.83m)
Wingspan 37ft (11.3m)
Empty weight 6,850lb (3,107kg)
Maximum take-off weight 10,600lb (4,808kg)
Performance
Maximum speed 390mph (628km/h) at 12,000ft (3,658m)
Range c.1,250 miles (2,012km) with 75 US gal external tanks
Service ceiling 31,000 ft
Armament 4 × .50in M2 Browning machine guns (two in each wing); one pylon beneath each wing for external fuel tank or a bomb of up to 500lb (227kg)
To begin with, NAA considered several potential names for the new aircraft, including the ‘Apache’. However, the British authorities succeeded in the adoption of the name Mustang, as confirmed by correspondence between NAA and the BPC in December 1940, copies of which are now held by the National Archives in Kew, London.
New arrivals
The first production series of RAF Mustangs was the Mk.I (NA-73), the initial example of which was given the British military serial number AG345. This version was armed with two synchronised .50 cal machine guns in the lower forward fuselage, one on each side, and three machine guns in each wing, one of .50 cal and the other two of either .30in or .303in. Power was provided by the Allison V-1710-39 of 1,150hp (as also used in the NA-73X as the V-1710-F3R). The original order for 320 Mk.I airframes was followed by 300 similar Mustang Mk.Is (NA-83).
By the time these aircraft started to arrive by sea at British ports during 1941, the Battle of Britain had been won and the RAF’s greatest need was for aircraft that were able to take the fight to the enemy on the Continent. To that end, the Mustang Mk.I became an important low-level attack aircraft. Adding to its growing importance, the type was configured to be a recce platform with an oblique F.24 camera mounted in the port fuselage, just behind the pilot.
However, a potentially more deadly Mustang was the next mark for the RAF: the Mustang Mk.Ia, armed with two 20mm cannon in each wing (NA- 91) and also powered by the Allison V-1710-39. The first example was FD418.
Different payments
The original 620 Mustang Mk.Is had been bought by Britain using hard currency. However, in March 1941, US President Franklin D Roosevelt successfully instituted the so-called Lend-Lease arrangements and, thereafter, all Mustangs for Britain were supplied differently. In effect, they were ordered by the US authorities and their procurement agencies as if they were for US military service, but were bought for and then allotted to Britain. The first Mustangs supplied under the Lend-Lease programme were the cannon armed Mk.Ia airframes.
The Japanese attack on Pearl Harbor in December 1941 brought the US into the war. Like Britain before it, the US found itself in dire need of many more warplanes. Eventually, 55 of the 150 Mustang Mk.Ia batch intended for the UK were requisitioned for US employment, plus two others retained by NAA.
The final Mustang version for the RAF was the Mk.II (NA-99). This was equipped with the more powerful Allison V-1710- 81 engine and was armed with two .50 cal machine guns in each wing. The first example was FR890, and 50 were procured, supplied to make up for the repossessed Mk.Ia airframes. Significantly, they were fitted with underwing pylons (one beneath each wing), which could carry a bomb of up to 500lb or external fuel tanks.
Useful employment
Allison-engined Mustangs served with RAF frontline squadrons from 1942 until the end of the war in Europe. Their considerable endurance, even without external underwing fuel tanks, allowed them to range freely over occupied France and the Low Countries, in the role that became their own: air-to-ground and recce, known as Tac/R.
The RAF organisation initially charged with these tactical operations was Army Co-operation Command. Created in December 1940, the squadrons of this body were equipped with Westland Lysanders and Curtiss Tomahawks. The Mustang represented a massive leap forward in both performance and firepower, as well as enhanced survivability for its pilots, compared to these two earlier types.
The first unit to become operational on the Mustang Mk.I was 26 Squadron at RAF Gatwick and a detachment at RAF Weston Zoyland in Somerset. It received its first Mustangs in the opening weeks of 1942, followed by several further units, including 241, 2, 16, 268, 613 and 400 Squadrons. The last of these was the first of three Royal Canadian Air Force (RCAF) units that eventually flew the early Allison-engined Mustangs, being joined later by 414 and 430 Squadrons.
The initial operational sorties over France were flown by 26 Squadron during May 1942, including participating in the ill-fated Dieppe landings (Operation Jubilee) in August 1942. During the combat on August 19, Fg Off Hollis Hills, an American volunteer with the RCAF’s 414 Squadron, claimed an Fw 190 in the vicinity of Dieppe to mark the very first enemy aircraft shot down by a Mustang.
A major change in the RAF’s organisation of tactical operations took place during 1943. Army Co-operation Command was replaced by the 2nd Tactical Air Force (2nd TAF or 2 TAF), and the Allison Mustang was one of the principal warplanes in this new command until the advent during 1944 of sufficient numbers of Hawker Typhoons, and later Tempests, for air-toground operations.
North American’s production manufacturing of Allisonengined Mustangs ceased during 1943, as a result of which the RAF’s fleet of these machines began to run down from late 1943 and during 1944. Nevertheless, RAF Allison Mustangs continued to perform in the Tac/R role and eventually some 21 squadrons flew the type. This included significant operations before, during and after D-Day in June 1944, when around 100 Allison Mustangs were still on strength. There were also overseas operations, with the type additionally being active in the Mediterranean theatre.
Allison Mustangs of several units were deployed during the infamous German strikes against Allied airfields on the Continent on January 1, 1945 (Operation Bodenplatte). A pilot of 268 Squadron claimed a twin-engined Junkers Ju 88 (possibly a Ju 188) which crashed near Utrecht. This is generally believed to be among the last, if not the very last, of the recorded air-to-air kills by an Allison-engined Mustang in World War Two.
Journey east
On May 8, 1945, when the war ended in Europe, two units (26 and 268 Squadrons) were still operating Allison Mustangs – a testament to the type’s longevity in RAF service.
Possibly ten Mustang Mk.I airframes were supplied from British stocks and sent to the Soviet Union. These were flown by Soviet test pilots, but it has never been confirmed if they were ever evaluated in actual combat.
It will be noted that the USAAC and its successor the US Army Air Force (USAAF) at first showed no official interest in the Mustang, explaining why the type only entered US service many months after the Allison Mustang made its debut with the RAF.
Nevertheless, as a part of the agreement for the Mustang to be made available for export, under an existing ‘release for foreign sale’ arrangement, two examples from the first production batch for Britain were officially procured for US testing at Wright Field in Ohio. They were designated XP-51, but were not the prototypes of the whole Mustang line, just evaluation aircraft from existing production.
These two XP-51 airframes were assigned the official US military serial numbers 41-038 and -039 (sometimes simply written as 41-38 and 41-39). Because they were actually production Mustang Mk.Is, they had the same armament and engine type as the Mk.I.
The first, 41-038, made its maiden flight on May 20, 1941, with Robert Chilton at the controls. It had been delivered to Wright Field during August that year. However, it was not until after the devastating attack on Pearl Harbor that the suddenly pressing need for large quantities of modern combat aircraft forced the USAAF to look far more seriously at the Mustang.
To begin with, part of the British order for the Mk.Ia was requisitioned, these aircraft becoming simply P-51 airframes without a prefix letter. At least some were prepared for combat as fast, low-level recce and light ground-attack aircraft.
The cameras fitted were US K-24 units, similar to the F.24 cameras installed in the RAF’s equivalent Mustangs. They were re-designated F-6A (‘F’ standing for ‘photographic’ in US military parlance).
Dive-bomber
Although the P-51/F-6A had been adopted by the USAAF very much as a requisitioned type from a foreign procurement, the USAAF eventually ordered its own Mustangs in 1942, but it was not as a fighter that the type was initially bought by the US military. In a bizarre twist, the first US purchase of the Mustang for the USAAF was as a dive-bomber. Reconfigured with retractable lattice-type air brakes above and below its wings, along with a pylon beneath each wing capable of carrying a 500lb bomb, the new type was designated A-36A. Armament comprised two .50 cal machine guns in each wing and a synchronised .50 cal gun in the lower forward fuselage on each side.
In recent years it has become fashionable to refer to this version as the ‘Apache’, but that was never its official name. In the field, air and groundcrews came to call the type ‘Invader’ (not to be confused with the twin-engined Douglas A-26 Invader) or they just simply used the generic name Mustang for the dive-bomber. In total, 500 A-36A (NA-97) airframes were ordered. They were built as A-36A-1-NA. The first of these was 42-83663, with the initial airframe flying on September 21, 1942, with Robert Chilton at the controls.
Dogfighting version
One further Mustang version was built specifically for the USAAF. This was the P-51A (NA- 99), which was the first true Mustang fighter for the service. It was the US equivalent of the Mustang Mk.II, and was therefore similar in armament and powerplant to its British counterpart. Procured in three batches, P-51A-1-NA, A-5-NA and A-10-NA, the total contracted was 310 airframes (although, as stated earlier, 50 of these were supplied to the RAF as Mustang Mk.II0) and the first example was 43-6003 – all of them were built by NAA at Inglewood, as indeed was every Allisonengined Mustang.
Some 35 P-51A airframes were configured for recce missions and were redesignated F-6B (and not F-6A as is sometimes claimed).
Recce action
The first Allison-engined Mustangs to fly operationally with the USAAF were the small number of P-51/F-6A recce airframes. Assigned to the 154th Observation Squadron of the 68th Observation Group in Tunisia, an F-6A made the first-ever combat sortie by a USAAF Mustang on April 9, 1943. This was some eleven months after the RAF had first used its Mustangs in combat.
Recce P-51/F-6As operated in the Mediterranean theatre until they were withdrawn during the summer of 1944. However, in northwest Europe, the F-6B played an important role in USAAF recce operations. They were operated by the 107th Tactical Reconnaissance Squadron (TRS) of the 67th Tactical Reconnaissance Group, US Ninth Army Air Force, based at RAF Middle Wallop, Hampshire. This unit was fully involved in the recce effort centred on the anticipated D-Day landings; following which it was moved to France and the Advanced Landing Ground A.4 Deux Jumeaux in late June 1944.
Bombing operations
Initial major A-36A operations were flown by the 27th Bomb Group (Light) on June 6, 1943, against Axis forces on the heavily defended Italian island of Pantelleria, some 43 miles east of the North African coast. The A-36A subsequently flew many combat missions in the Mediterranean theatre, the 27th being re-designated as a Fighter-Bomber Group (FBG) and later joined by the 86th FBG there. The 111th TRS also had several A-36As on strength, in addition to its P-51/F-6A airframes. The A-36A, like all Allison-engined Mustangs, could look after itself in aerial combat, with several USAAF pilots scoring comparatively well on the type. The 27th FBG achieved at least 45 confirmed aerial victories, with Lt Michael T Russo being unique in achieving ace status on the A-36A.
In the China-Burma-India (CBI) theatre, the 311th FBG also flew the A-36A, in comparatively small numbers. Several were loaned to the RAF in the Mediterranean.
Fighter progress
The first USAAF unit to take the P-51A into action was the 311th FBG (later 311th Fighter Group) in the CBI, operating over Burma and sometimes using Kurmitola as its forward base. The unit’s initial major operation with Mustangs was on November 25, 1943, when the group’s A-36As and P-51As were involved in attacks that challenged Japanese aerial power in central Burma. However, its aircraft were used increasingly against the Japanese as fighters, with the group’s Mustangs escorting the USAAF’s B-25 Mitchell medium bombers.
Several of its pilots became aces while flying the P-51A. The acknowledged highest-scorer on the type was Capt James England, with eight confirmed ‘kills’ over Japanese aircraft.
In China, the 23rd Fighter Group operated P-51As against the Japanese. One further unit flew the Allison-engined Mustang in the CBI, this being the 1st Air Commando Group, specifically on fighter and airto-ground operations against the Japanese in Burma.
