The P-51 Mustang

The bombers' "Little Friend"

Today's article focuses on the P-51 Mustang, often nicknamed "Little Friend" for the invaluable service it provided escorting Allied heavy bombers over Europe. The P-51 was one of the best all-around fighters, and one of the most recognizable American warplanes of World War II. And yet, there might be things you didn’t know about it. Did you know, for example, that despite being a quintessentially American fighter, its very inception was thanks to the British war effort?  Read on for more about this truly outstanding icon of World War II aviation!

Britain suffered from a serious shortage of fighter craft at the beginning of World War II, which would become all the more acute with the fall of France, the Battle of Britain, and the specter of a German invasion. (Read our earlier article) The government was looking to buy a large number of American fighters to bolster the nation's defenses, but only one particular type was being considered: the Curtiss P-40 Warhawk, named "Tomahawk" in British service. The P-40 was not a great plane, but it was the only American fighter at the time that was considered good enough against first-rate enemies like the Luftwaffe.

The Curtiss-Wright Corporation's manufacturing plant, however, was already running at full capacity, so the British decided to try and get another corporation to produce the P-40 for them under license. As it happened, North American Aviation (NAA) just approached Sir Henry Self, the civil servant in charge of Royal Air Force (RAF) production and development, about selling the company's new medium bomber, the B-25 Mitchell (which became famous with the Doolittle Raid (Read our earlier article)), to Britain. The RAF was far more concerned with intercepting incoming German bombers than with launching its own bombing raids at the time, so Self demurred, but made a counterproposal: NAA should build the P-40 for Britain under license from Curtiss. The British Purchasing Commission was initially reluctant to take a gamble with a company that had no experience building fighters, but eventually acquiesced on the condition that NAA purchase the P-40 technical drawings and wind tunnel test data and study those before designing their own aircraft. They also insisted on the same Allison V-1710 engine that the P-40 used.

The P-51 was designed by German-Austrian engineer Edgar Schmued. It first flew 149 days after signing the contract, which was a remarkably quick development cycle even by World War II standards. It could carry a lot of fuel, it handles well, and it was armed with a pair .50 caliber Browning machine guns (Read our earlier article) in the nose and four .30 caliber ones (Read our earlier article), two in each wing. It did, however, also have a significant weakness. The Allison V-1710 engine had a single-supercharger, whose performance dropped off sharply above an altitude of 15,000 feet (4,600 m). This made early versions of the plane unusable as an interceptor or a bomber escort, since bombing raids over Europe regularly flew at higher altitudes than that.

Early production models intended for British use changed the armament. All Mustangs lost the two machine guns in the nose. Some had the four wing guns upgraded to .50 calibers, while others were armed with four 20 mm Hispano autocannons, a weapon well-liked by the RAF but only used by the United States Army Air Forces (USAAF) in a very limited scope. While these early versions were poor performers at high altitudes, they were excellent combat craft closer to the ground, even exceeding the Supermarine Spitfire Mk.V. (Read our earlier article) They performed admirably as low-level reconnaissance planes and as high-speed ground attack craft in raids over Europe as well as in Southeast Asia and North Africa, where warplane use revolved around providing close air support to ground forces. The European raids, codenamed Rhubarb raids, involved aircraft crossing the English Channel 50 ft (15 m) above sea level, zigzagging every 6 minutes over land to throw off German interception attempts, strafing or bombing locomotives, barges, aircraft on the ground and other such targets, then using their superior low-level speed to escape. Mustangs destroyed 200 locomotives, 200 canal barges and an unknown number of aircraft in the first 18 months of the Rhubarb raids, only losing 8 planes in the process. British and Canadian Mustangs also supported the disastrous Dieppe Raid in August 1942 (Read our earlier article), and early versions of the plane continued to attack V-1 launch sites (Read our earlier article) even into 1943-44. 

The Mustang's other big weakness beyond high-altitude performance was political. As pointed out by U.S. Army Air Corps Assistant Air Attaché Major Thomas Hitchcock, "Its development in this theatre has suffered for various reasons. Sired by the English out of an American mother, the Mustang has no parent in the Army Air Corps to appreciate and push its good points. It does not fully satisfy good people on both sides of the Atlantic who seem more interested in pointing with pride to the development of a 100% national product..."  Since the U.S. military played no role in the plane's inception, it took them a while to recognize the strengths of the design. It took a personal intervention by General Henry "Hap" Arnold, Chief of the Army Air Forces, for the USAAF to hold back several dozen planes from the British order for testing and use.

Production of the Mustang ran into financial difficulties when the Lend-Lease contract ran out of funds. The USAAF was already considering adopting the plane by this time, but had already used up its budget for fighter appropriations for the financial year of 1942. The USAAF still had money available for attack aircraft, so, not wanting to let the NAA manufacturing line and the experienced assembly crews go to waste, the Air Forces decided to request a dive bomber version of the plane. The result was the A-36, sometimes unofficially called the "Invader" (but not to be confused with the Douglas A-26 Invader), but most often simply referred to as "Mustang." It was essentially the same plane as the fighter, but up-gunned with six .50 caliber Browning M2-s instead of four, carrying two 500 lb (230 kg) bombs, and equipped with dive brakes on the wings. 500 of these planes were made, and they served well in the liberation of Sicily and mainland Italy, as well as in the China-Burma-India theater. An urban legend claims that the dive brakes were so dangerous they were wired shut to prevent pilots from opening them. As far as it can be determined, something like that might have happened in a training group, but not in combat units, which used the dive slats just fine.

Though early versions of the P-51 proved to be formidable warplanes at low altitudes, the lack of high-altitude performance was still a sore spot. The excellent British Rolls-Royce Merlin engine (which also powered the Spitfire), was a strong candidate to replace the Allison engine. Experiments with the Merlin 61 gave the plane an unexpected boost in performance: its top speed increased from 390 mph (630 km/h) at 15,000 ft to an intimidating 440 mph (710 km/h) at 28,100 ft, making it one of the fastest propeller-driven planes of the war.

After some experimentation, the P-51D became the definitive version of the plane. Besides the new engine, it also sported a new type of canopy. The old razorback design offered poor backward visibility, so it was changed to a “tear drop” (or “bubble”) canopy shape that gave the pilot almost 360° vision. The bomb racks and the six .50 caliber machine guns already implemented for the A-36 became the standard for this and later versions. The P-51D (and the P-51K, manufactured in another factory and identically except for a different, worse propeller) began to see service with the USAAF in Europe in mid-1944. The legendary fighter ace and test pilot Chuck Yeager was one of the many servicemen who flew the P-51D. On October 12, 1944, he shot down five German fighters with his plane Glamorous Glenn II in one sortie, becoming “ace in a day.”

With its long range, excellent high-altitude performance and an engine that was available in large numbers, the P-51D became the ideal escort for American bombing raids deep into German-occupied Europe. Unescorted bomber formations, in which bombers were supposed to cover each other with overlapping fields of fire, were suffering heavy losses from German flak fire from the ground and interceptors in the air.  One of the strategic goals of the Allies was to cripple the Luftwaffe: bomber formation heading for major German cities would force the Germans to send up their interceptors, which would then be destroyed by the escorts.

Major General James Doolittle, head of the 8th Air Force, had the fighter escorts fly far in advance of the bombers in “fighter sweeps,” destroying German aircraft before they could present a threat to the bomber formations. Being left alone was unpopular with the bomber crews, but the tactic achieved air supremacy by June 1944. Mustangs later returned to their earlier role of low-level ground attackers, despite their liquid-cooled engines being a weak spot: even small arms fire could damage a plane in a strafing or bombing run, and the loss of cooling liquid would cause the P-51 to crash before making it home – the Republic P-47 Thunderbolt did not have this weakness, thanks to its air-cooled engine.

The most bizarre version of the P-51 was born out of the conditions of the Pacific theater. Much of the American effort there was aimed at capturing islands from where the new B-29 Superfortress could reach and bomb the Japanese Home Islands. These bombers, however, needed escorts, and even the Mustang didn’t have the range – or the stamina. Even if he had enough range with the help of external fuel tanks, a single pilot locked in a small cockpit would suffer terribly during the long flight such missions would entail, and his combat performance would drop. The solution was the F-82 Twin Mustang, which was essentially two P-51 fuselages placed side by side and connected by a central wing. The prototypes had fully equipped cockpits in both fuselages: the man on the left was the pilot, and the man on the right the pilot-navigator, who could take over control of the plane so the pilot could rest. Several post-World War II versions of the F-82 had the cockpit removed from the right-hand side and replaced by a radar operator’s position. These planes also carried a long radar pod, unflatteringly nicknamed the “long dong” under the center wing. 

Around 270 Twin Mustangs were built, but they came too late for their intended role, only entering service in 1946. It did, however, see service early in the Cold War, and particularly in Korea, during those years when jets were still in baby shoes and suffered from short operational range. When equipped with external fuel tanks, the Twin Mustang could take off from London, fly to Moscow, loiter over the target for 30 minutes, and fly home. Such a mission never took place, but one F-82 did fly 5,000 miles (8,100 km) non-stop from Hawaii to New York in 14 hours and 30 minutes, setting the record for both the longest non-stop flight for a propeller-driven fighter, and for the fastest propeller-driven flight over such range.

Both the Twin Mustang and its more traditional siblings saw action in Korea, where they could operate from Japan, a feat their early jet contemporaries didn’t have the range for. In fact, the first U.S. air combat mission in Korea occurred on June 25, 1950, when a reconnaissance flight of F-82s confirmed that North Korean forces including tanks and truck have crossed the border to South Korea. 

The F-51 (the Cold War designation of the P-51, “fighter” instead of “pursuit”) was retired from U.S. service by the end of the 50s. Of the more than 15,000 planes produced, hundreds entered the civilian market and were modified for air racing or personal use, while many others continued to see military service in other nations including Israel, Indonesia, Cuba, Australia and New Zealand. Several specimens of one particular civilian conversion, the Cavalier Mustang, were also converted back to military use and given to South American countries for counterinsurgency use. One particular civilian Mustang, The Rebel, set an altitude record of 42,568 ft (12,975 m) for piston-powered aircraft between 6,600 and 13,200 lb (3,000 to 6,000 kg) in 2013. One great present-day fan of the Mustang is legendary actor Tom Cruise, who fell in love with flying during the shooting of Top Gun in 1986, got his pilot's license in 1994, and owns the P-51 Kiss Me Kate, named after his ex-wife Katie Holmes. He even flew it in the final scene of the recent Top Gun 2 movie.

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