North American P-51 Mustang

The Mustang was born of a British emergency. In April 1940 the RAF’s purchasing commission, desperate for fighters, approached North American Aviation to build Curtiss P-40s under licence; “Dutch” Kindelberger’s company instead offered to design a wholly new and better aircraft around the same engine, and did so with astonishing speed. The prototype NA-73X was rolled out in just 117 days and first flew on 26 October 1940.

The result was aerodynamically superb: clean, fast, and fitted with an advanced laminar-flow wing — a new low-drag aerofoil developed with the NACA — together with a neatly designed belly radiator whose “Meredith effect” recovered cooling drag as a little thrust. But it had a fatal flaw. Its Allison V-1710, lacking a two-stage supercharger, gasped for breath above about 4,500 m, and the early Mustangs were relegated to low-level reconnaissance and ground attack with the RAF. The finest airframe of the war was, at first, fitted with the wrong engine.

The transformation came from Britain. In 1942 Rolls-Royce engineers, struck by the airframe’s quality, tried mating it to the two-stage supercharged Merlin 61 — the same engine that had revived the Spitfire — and the change was electrifying. At a stroke the Mustang gained the high-altitude performance it had always lacked, becoming faster above 7,000 m than almost anything in the sky while keeping the phenomenal fuel economy of its clean design.

Put into mass production in the United States with the Merlin built under licence by Packard as the V-1650, the aircraft became the P-51B and P-51C. The definitive P-51D added a cut-down rear fuselage and a frameless bubble canopy for all-round vision, plus a sixth .50-calibre gun. Above all it could carry an enormous fuel load — deep internal tankage plus two drop tanks — the single quality that would change the air war over Germany.

Around 15,000 Mustangs were built in all. The Allison-engined early P-51 and A-36 dive-bomber carried the design into action at low level in 1942–43; the Merlin-engined P-51B and C took it into the escort war in 1943; and the P-51D of 1944 became the definitive model and the classic Mustang silhouette.

The line ran on into the lightweight P-51H, one of the fastest piston fighters ever built, the camera-carrying F-6 reconnaissance versions, and the twin-fuselage P-82 Twin Mustang that carried the concept into the jet age. Few airframes ever proved so adaptable across so many roles.

By the autumn of 1943 the American daylight bombing campaign was in crisis. The self-defending formation of B-17 Flying Fortresses — the doctrine the Eighth Air Force had staked everything on — was being torn apart: on the second Schweinfurt raid of 14 October 1943, “Black Thursday,” 60 bombers were shot down out of 291, and deep raids beyond fighter cover were suspended. The bombers could not survive over Germany without escort, and no Allied fighter had the legs to take them there and back.

The Mustang was the answer, and it turned on a simple arithmetic of range. With two drop tanks a P-51D had a combat radius of around 1,500 km — Berlin and beyond — at a cruise the heavy bombers could live with, something neither the Spitfire nor the shorter-ranged P-47 could yet manage. For the first time the bombers could be shepherded all the way to the target and home again by a fighter that, once its tanks fell away, could out-fly the defenders waiting for them.

The Mustang did not merely protect the bombers; it destroyed the force sent up to stop them. In January 1944 General Jimmy Doolittle, taking over the Eighth Air Force, freed the escorts from rigid close formation with a new order: their job was to pursue and destroy the German fighters wherever they could be found, turning every raid into bait for a trap. The bomber stream became the anvil; the Mustangs, ranging ahead and above, became the hammer.

The results were decisive within months. In the “Big Week” battles of February 1944 and over Berlin in March, the Jagdwaffe was bled white — losing not just aircraft but irreplaceable experienced pilots faster than its schools could produce them. By the Normandy landings in June the Allies effectively owned the sky over Western Europe. Credited with nearly 5,000 air-to-air victories in the European theatre — more than any other American fighter — the Mustang had won the strategic air war’s central battle: air supremacy over Germany itself.

The Mustang’s war ran far beyond the skies of Germany. In Italy it equipped the Tuskegee Airmen of the 332nd Fighter Group — the “Red Tails,” the US Army’s first Black fighter pilots — who escorted the Fifteenth Air Force’s bombers over southern Europe and built a formidable reputation doing it. RAF squadrons flew Mustangs too, from armed reconnaissance to the hunt for V-1 flying bombs.

In the Pacific it flew some of the most punishing missions of the war. From Iwo Jima, taken at terrible cost in early 1945, P-51s escorted the B-29s to the Japanese home islands — seven- and eight-hour flights over open ocean with no room for error. And the Mustang outlived the war it was built for: it fought again over Korea in the ground-attack role and served in air forces around the world into the 1980s, a longevity few wartime designs could match.

The P-51 Mustang began as a rushed answer to a British requirement and ended the war as, by wide agreement, the finest all-round fighter of the conflict. Fast, elegant and astonishingly long-legged, it solved the single greatest problem of the strategic air war — how to protect the bombers over the heart of Germany — and in doing so helped break the back of the Luftwaffe.

It is remembered as the definitive American piston fighter, and the record supports the claim: an airframe and an engine designed in different countries, combined to produce the one quality — range — that resolved the central problem of the strategic air war. The Mustang flew on into the jet age, fought again over Korea in the ground-attack role, and served with foreign air forces into the 1980s.

• Paul A. Ludwig, P-51 Mustang: Development of the Long-Range Escort Fighter (Classic Publications, 2003).
• Roger A. Freeman, The Mighty Eighth (Cassell) — the standard history of the Eighth Air Force.
• Robert W. Gruenhagen, Mustang: The Story of the P-51 Fighter (Arco).
• Jerry Scutts, Mustang Aces of the Eighth Air Force (Osprey, Aircraft of the Aces).