America’s Misunderstood Mustang: The Allison-Powered Fighter That History Forgot

Two engines, two chapters—but only one has been remembered. The story of the Allison-powered Mustang reveals why overlooking the lesser-known version distorts our understanding of aviation’s most celebrated fighter.

The Shadow of Success

Walk into any aviation museum or open any history book dedicated to World War II fighters, and you’ll encounter the iconic image: a sleek P-51D Mustang, its nose painted in brilliant invasion stripes, powered by a liquid-cooled Rolls-Royce Merlin engine. That aircraft earned its legendary status through relentless high-altitude escort work that saved American bomber fleets from Luftwaffe fighters across European skies. But this singular narrative has cast a long shadow over an equally important—and fundamentally different—chapter of Mustang aviation history.

The Allison-engined Mustang, which preceded its celebrated Merlin-powered cousin by years and served with distinction throughout the war, has been largely forgotten. Where the Merlin Mustang became the stuff of warbird legend, the Allison version languished in historical obscurity, often dismissed as an inferior predecessor rather than recognized for what it truly was: a revolutionary low-level attack and reconnaissance aircraft that transformed tactical air operations in multiple theaters.

This oversight is not merely academic. It obscures the genuine origins of the Mustang and fundamentally misrepresents the aircraft’s design philosophy and intended purpose.

Birth of a Necessity

The Mustang’s creation sprang from British pragmatism, not American initiative. As 1939 turned to 1940 and Nazi Germany tightened its stranglehold on Europe, Britain faced an acute crisis. The Royal Air Force was converting rapidly to the excellent Supermarine Spitfire and Hawker Hurricane—aircraft that would prove their mettle in the coming Battle of Britain—but production simply couldn’t keep pace with losses. More fighters were needed, and they needed to come from somewhere outside the beleaguered British Isles.

That source was the neutral United States. In November 1939, Britain established the British Purchasing Commission (BPC), a buying organization tasked with acquiring American military equipment. The BPC identified one immediate target: the Curtiss P-40 series, a capable fighter then entering American service. But when representatives approached North American Aviation to license-build P-40s, they encountered something unexpected.

North American’s leadership, particularly its forward-thinking design team, rejected the proposition outright. License-building another company’s fighter held no appeal. Instead, they made a bold counterproposal: allow us to design and manufacture an entirely new fighter, purpose-built for RAF requirements. The BPC, recognizing opportunity when presented, accepted.

The decision proved momentous. Within weeks of that agreement in early 1940, North American’s designers had sketched the basic layout of what would become the Mustang. The engine selection reflected practical availability: the liquid-cooled Allison V-1710 V12, identical to the powerplant in the P-40. At that moment, no arrangement existed for American manufacture of the Rolls-Royce Merlin engine—that development lay years in the future.

The Allison promised solid performance at the altitudes the RAF desperately needed: medium and low level. The RAF’s operational doctrine, shaped by the Battle of Britain and its ongoing struggle for air superiority in limited engagements, emphasized tactical flexibility and the ability to project power across the Channel into occupied Europe. The Mustang was designed to excel in precisely that environment.

A Prototype Takes Flight

The company designation was NA-73. The prototype, NA-73X, carried civil registration NX19998—notable because it was company-funded and therefore carried no military serial number. On October 26, 1940, at Mines Field (now Los Angeles International Airport), test pilot Vance Breese advanced the throttles and the sleek fighter lifted into the California sky.

The results were immediately promising. The NA-73X demonstrated speed, maneuverability, and a notably clean flying character. More significantly, it showed few vices—a critical attribute for a fighter entering service with a foreign air force under wartime pressure.

The British were sufficiently impressed that they had already committed to the design, even before first flight. In May 1940, just months after the initial conversations between the BPC and North American, Britain signed up for 320 aircraft, purchasing them directly off the drawing board. This decision made the Mustang unique among British warplanes: it entered service without meeting any formal Air Ministry specification. It was commissioned on faith and technical promise alone.

The name itself carries a certain irony. North American’s designers considered several options, including “Apache.” But the British authorities intervened, insisting on “Mustang”—a name they believed better suited the spirited character of the new machine. Correspondence between North American and the BPC, now archived at the National Archives in Kew, London, confirms this exchange occurred in December 1940.

The Production Mark I

The first production variant, the Mustang Mk.I (NA-73), retained the Allison V-1710-39, rated at 1,150 horsepower—a modest figure compared to what would come later, but sufficient for the role envisioned. Initial armament comprised two synchronized .50-caliber machine guns in the lower fuselage and three additional machine guns in each wing: one .50-caliber paired with two weapons chambered in either .30 or .303 caliber.

The original order for 320 aircraft was followed by an additional 300 similar examples, all bearing the NA-83 designation. By 1941, these Mustangs began arriving at British ports aboard transatlantic convoys, their wooden crates navigating waters increasingly patrolled by German U-boats.

The timing of their arrival proved fortuitous in ways different from what Britain initially expected. The Battle of Britain was won by the time these fighters began entering RAF service. The Luftwaffe had abandoned its invasion ambitions, and the air war transformed into something far more attritional: cross-Channel operations, raids into occupied territory, and the relentless campaign to establish air superiority over continental Europe. The Mustang’s capabilities—its range, its agility, its speed at lower altitudes—made it ideally suited for this new operational environment.

The aircraft earned its reputation quickly. Fitted with an oblique F.24 camera mounted in the fuselage just aft of the cockpit, the Mustang Mk.I became an invaluable reconnaissance platform. But its greater significance lay in air-to-ground operations. Where earlier tactical aircraft like the Westland Lysander and Curtiss Tomahawk had served the Army Co-operation Command with limited speed and firepower, the Mustang represented a quantum leap in both performance and destructive capability. Pilots found it a capable fighter when circumstances demanded, yet efficient and long-ranged when employed on the ground-attack missions that increasingly defined tactical air warfare.

The Mustang Mk.Ia (NA-91) pushed the concept further. Armed with two 20-millimeter cannon in each wing, it offered substantially increased firepower for strafing and close-support operations. The first example, FD418, entered RAF service in 1941.

Lend-Lease and Requisition

In March 1941, President Franklin D. Roosevelt successfully maneuvered the Lend-Lease program through a reluctant Congress. This revolutionary arrangement transformed the relationship between America and its British ally. Rather than Britain paying precious hard currency for every weapon, American equipment would henceforth be manufactured at American expense and supplied to Allied powers through a complex system of loans and reciprocal arrangements.

The implications for the Mustang program were immediate. All subsequent aircraft ordered by Britain would flow through this new mechanism. More significantly, as the United States entered the war following Pearl Harbor, the calculus changed dramatically. Of the 150 cannon-armed Mk.Ia aircraft originally designated for the RAF, 55 were requisitioned for American service. The suddenly urgent need for modern combat aircraft overrode any previous agreements regarding foreign orders.

The final RAF variant was the Mk.II (NA-99), powered by the more robust Allison V-1710-81 engine and armed with two .50-caliber machine guns in each wing. These aircraft featured underwing pylons capable of carrying either 500-pound bombs or external fuel tanks—equipment that would prove essential for the long-range tactical operations that came to define Allison-engined Mustang operations in Europe.

An Unexpected Role: The Dive-Bomber

The U.S. Army Air Forces’ initial engagement with the Mustang took a peculiar turn. Rather than ordering the aircraft as a fighter, the USAAF’s first purchase came in an unexpected guise: a dive-bomber variant. This seemed illogical to many observers then and seems equally so in hindsight.

The aircraft received the designation A-36A (NA-97). The configuration included retractable lattice-type air brakes mounted above and below the wings, along with underwing pylons designed to carry 500-pound bombs. Armament consisted of two .50-caliber machine guns in each wing and synchronized .50-caliber weapons in the lower fuselage on each side.

The A-36A would later acquire the nickname “Apache” in some historical accounts, though this designation was never official. Ground and flight crews called it the “Invader”—a term that occasionally generates confusion with Douglas’s twin-engined A-26 Invader. More often, they simply referred to it as a Mustang. In total, 500 A-36A airframes were manufactured. The first flew on September 21, 1942, with test pilot Robert Chilton at the controls.

The A-36A’s operational debut came on June 6, 1943, when the 27th Bomb Group (Light) attacked Axis positions on the heavily defended Italian island of Pantelleria, located 43 miles east of the North African coast. This campaign marked the beginning of extensive Mediterranean operations that would continue throughout 1943 and into 1944. The 27th was subsequently redesignated the 27th Fighter-Bomber Group, joined later by the 86th Fighter-Bomber Group in the same theater.

Despite its dive-bomber designation, the A-36A proved remarkably effective as a fighter when aerial combat became necessary. The 27th Fighter-Bomber Group achieved at least 45 confirmed aerial victories while operating the aircraft. Lieutenant Michael T. Russo became the only pilot to achieve ace status—five or more confirmed kills—flying the A-36A variant, a distinction that underscores the aircraft’s fundamental soundness as a fighting machine.

The Fighter’s Entry

The P-51A (NA-99)—essentially the American equivalent of the British Mk.II—represented the first true fighter variant ordered specifically by the USAAF. Armed identically to the Mk.II with four .50-caliber machine guns and powered by the Allison V-1710-81, the P-51A combined the proven airframe with enhanced engine power. The USAAF procured 310 of these aircraft across three production batches, though 50 were diverted to the RAF as replacement aircraft for the requisitioned Mk.Ia machines.

Among these early American fighters were 35 P-51A airframes configured specifically for reconnaissance duties. Redesignated F-6B (an identification sometimes confused in historical references with the earlier F-6A designation), these aircraft carried the same K-24 cameras installed in their RAF counterparts, allowing them to conduct high-speed photographic reconnaissance missions across contested airspace.

The first operational sortie by a USAAF Allison-engined Mustang came on April 9, 1943—a reconnaissance mission by an F-6A of the 154th Observation Squadron in Tunisia, more than eleven months after RAF Mustangs had first engaged in combat. However, the first major combat operations involving USAAF Allison-engined Mustangs in the fighter-bomber role came later that spring, beginning with the A-36A’s Pantelleria campaign on June 6, 1943. These parallel operational tracks—reconnaissance variants and combat variants—would continue to define USAAF Allison-engined Mustang deployments throughout the remainder of the war.

In Northwest Europe, reconnaissance Mustangs of the 107th Tactical Reconnaissance Squadron (67th Tactical Reconnaissance Group, Ninth Army Air Force) played a critical role in the air-to-air reconnaissance effort that culminated in the D-Day landings of June 6, 1944. Operating from RAF Middle Wallop in Hampshire, these pilots penetrated enemy airspace at low level and high speed, bringing back photographic intelligence essential to Allied planning.

The tactical reconnaissance effort continued after the lodgment in Normandy. The 107th Tactical Reconnaissance Squadron relocated to Advanced Landing Ground A.4 Deux Jumeaux in late June 1944, from which it conducted ongoing reconnaissance operations in support of the breakout from the beachhead and the subsequent advance across France and Belgium.

The War in Multiple Theaters

Perhaps the most significant deployment of Allison-engined Mustangs occurred in the China-Burma-India theater. The 311th Fighter Group (which had previously operated as the 311th Fighter-Bomber Group) flew both A-36A dive-bombers and P-51A fighters against Japanese forces in Burma and China. The unit’s initial major operation with Mustangs came on November 25, 1943, when A-36As and P-51As were committed to attacks that directly challenged Japanese aerial supremacy in central Burma.

As operations progressed, the 311th Fighter Group increasingly employed its Mustangs in the fighter role, providing escort for USAAF B-25 Mitchell medium bombers and engaging Japanese fighters in air-to-air combat. Several of the group’s pilots achieved ace status on the P-51A, testament to the aircraft’s fundamental soundness as a fighting machine. Captain James England emerged as the highest-scoring American pilot on the Allison-engined variant, with eight confirmed victories against Japanese aircraft.

In China proper, the 23rd Fighter Group also operated P-51A Mustangs against Japanese forces. Additionally, the 1st Air Commando Group flew Allison-engined Mustangs on fighter and ground-attack missions throughout Burma, extending the type’s operational reach into the most challenging air campaign in the Far East.

The First Victory at Dieppe

The earliest recorded air-to-air victory involving a Mustang occurred during the ill-fated Dieppe landings of August 19, 1942. Flying Officer Hollis Hills, an American volunteer serving with the Royal Canadian Air Force’s 414 Squadron, claimed an Fw 190 in the vicinity of Dieppe, marking the very first enemy aircraft shot down by a Mustang in any air force. This distinction, though achieved at the cost of heavy casualties during the abortive raid, underscores the aircraft’s capabilities as a fighter despite its primary role as a low-level attack platform.

The Overlooked Legacy

The RAF eventually operated the Allison-engined Mustang with some 21 squadrons, a figure that speaks to its operational importance and the confidence British commanders placed in the type. The aircraft remained in frontline service until the end of the war in Europe, with two squadrons—26 Squadron and 268 Squadron—still operating them on May 8, 1945, when the war formally concluded.

On January 1, 1945, during Operation Bodenplatte, the German Luftwaffe’s massive strike against Allied airfields across occupied Europe, Allison-engined Mustangs of several RAF squadrons were engaged in defense. A 268 Squadron pilot claimed a Junkers Ju 88 (possibly a Ju 188) near Utrecht in what is generally considered among the last, if not the very last, recorded air-to-air victory by an Allison-engined Mustang during World War II.

Possibly ten Mustang Mk.I airframes were supplied from British stocks to the Soviet Union, where they were evaluated by Soviet test pilots. Whether they saw actual combat remains unconfirmed—documentation from the Eastern Front during that period is frustratingly incomplete.

The Allison-engined Mustang’s operational record across three theaters and two air forces over nearly four years of warfare speaks for itself. Yet in the popular imagination, the Mustang exists as a singular entity: the Merlin-engined high-altitude fighter. The earlier, quite different aircraft that established the groundwork for that legendary machine has faded into the background, relegated to a footnote in a story that should more properly be told as a two-chapter narrative.

Understanding the Distinction

The historical oversight is understandable but regrettable. The Merlin-engined P-51D and its variants became the stuff of legend because they performed a mission of overwhelming strategic importance: protecting American heavy bomber streams as they ranged deep into German territory. That role saved untold American lives and fundamentally altered the air war over Europe. The achievements of those pilots—men like Don Gentile, Robin Olds, and countless others—deservedly occupy a central place in aviation history.

But that significance should not obscure the legitimate accomplishments of the aircraft and pilots who came before. The Allison-engined Mustang was not a failed experiment awaiting redemption through engine swap and redesign. It was a purpose-built tactical aircraft that performed its assigned mission with skill, courage, and considerable effect. From the reconnaissance photographs that guided bombing campaigns to the dive-bombing attacks on enemy installations to the low-level strafing runs that supported ground operations, Allison-engined Mustangs contributed substantially to Allied victory.

The aircraft’s range—remarkable for a single-engine fighter of the era—allowed it to project power across hundreds of miles of contested airspace. Its speed at medium and low altitudes surpassed nearly every contemporaneous fighter it encountered. Its reliability and maintainability, even under the austere conditions of forward airfields, earned the respect of ground crews and pilots alike.

The Allison-engined Mustang represented a specific response to a specific set of operational requirements. It succeeded not because it was a fighter that someone thought should also do reconnaissance and ground attack work, but because those requirements shaped its design from inception. When the Merlin engine became available and American strategic doctrine shifted toward deep-penetration bomber escort, a different aircraft became necessary. That the P-51D Mustang excelled at high-altitude fighter work does not diminish the achievements of the aircraft that preceded it.

Understanding this distinction is essential to properly comprehending the Mustang’s genuine place in aviation history. It is not merely the lesser version of a legendary aircraft. Rather, it is a different aircraft, optimized for a different role, that executed that role with distinction and contributed meaningfully to Allied victory across three theaters of war. The shadow cast by the Merlin-engined variant has been long enough. The Allison-engined Mustang deserves to be recognized not as a footnote to aviation history, but as a chapter in its own right.