If a single airplane has captured the public imagination more than any other, it is undoubtedly the North American P-51 Mustang fighter. In the minds of many, including the young fighter pilots who flew it during the final year of combat in Europe, it was the P-51 that allowed the Allies to attain complete air superiority over Europe.
Many of the accolades bestowed upon the Mustang are not quite in tune with the facts, however. The airplane truly did develop into an outstanding fighter—but it did not start out that way. Oddly enough, the design of the Mustang came about completely by accident and was more the result of corporate pride than military necessity. Its subsequent development also was more accidental than by design. The U.S. Army never even wanted the airplane, and the British were not happy with it when they got theirs.
North America Makes Their Own Fighter
Before America entered the war, the British Purchasing Commission placed orders for a variety of American-produced military aircraft, including Curtiss fighters powered by Allison engines, which had been designated as the P-40 Tomahawk by the U.S. Army Air Corps. Curtiss lacked the facilities to meet the British orders and made an offer to North American Aircraft to have them manufacture some planes under license. North American’s president, West Virginian James S. “Dutch” Kindelberger, was not happy with the offer. He proposed instead that his company produce an entirely new fighter that would be built around the same Allison V-1710 engine that powered the P-40. Kindelberger believed his company could produce an aerodynamically superior airplane that could utilize new mass production methods that were just coming into use in the American aircraft industry.
The British asked for a preliminary design study. North American promised that a prototype would be ready to fly in an amazing four months! The North American management convinced Curtiss to furnish them data from the design of their P-40, thus cutting several months of preliminary design from the new fighter project. The company promised the British that they would begin deliveries in January 1941 and would produce 50 airplanes a month through the end of 1941. The British gave the airplane its name—Mustang—apparently adopting the name of the wild ponies that roamed the American West, although no reason for the choice is known. To cut down on production time, North American elected to use a non-turbocharged version of the Allison V-1710 engine, a move that would reduce the airplane’s high-altitude performance.
A Design Ruined by an Underpowered Engine
When the first Mustangs arrived in England, Royal Air Force test pilots quickly discovered that although the new fighter was very agile and fast its performance began to degrade at altitudes above 15,000 feet as the normally aspirated Allison engines lost power. Consequently, the RAF decided to assign the Mustangs to its Army Cooperation Command, which had previously used the light and maneuverable Westland Lysander as its primary aircraft.
The Mustangs were equipped with cameras and assigned to the tactical reconnaissance role, in which the airplane continued for the duration of the war. The first operational use of the RAF Mustangs was in support of the disastrous Dieppe raid in August 1942. It was also in the support role that the U.S. Army Air Corps assigned its first Mustangs, a batch of 57 airplanes that was diverted from the British production immediately after the attack on Pearl Harbor.
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Perhaps prompted by the RAF’s use of the Mustang in the Cooperation Command, the U.S. Army decided to adapt the Mustang as a dive-bomber. At the time, the Army’s standard dive-bomber was the Douglas Dauntless, which the Army designated as the A-24. Unfortunately, their lack of defensive capabilities led to heavy losses among the A-24s in the Southwest Pacific in early 1942, a factor that no doubt influenced the decision to seek a more maneuverable and better armed design for dive-bombing.
Dive brakes and hard points to carry bombs up to 1,000 pounds were added to the basic design to convert the plane into a dive-bomber, which was designated as the A-36. The 27th and 86th Bombardment Groups (Light) were equipped with A-36s and sent into combat in North Africa in the spring of 1943. RAF Mustangs also saw combat duty in North Africa, although the primary tactical fighters used by the British in North Africa were Curtiss Kittyhawks and Hawker Hurricanes. The 311th Bombardment Group, also equipped with A-36s, was sent to China. Over time, the U.S. Army came to believe that the value of the dive- bomber had been overestimated, and even though more than 300 A-36s were built, they were all eventually replaced either by fighters or light and medium bombers. Dive-bombing would remain popular in the Navy and Marine Corps, but the Army abandoned the practice.
Transforming the Mustang With the Rolls Royce Merlin Engine
With the decision to assign its new Mustangs to the Cooperation Command, the Royal Air Force elected to continue the development of the already famous Supermarine Spitfire as its primary interceptor. Still, some of the RAF test pilots believed that with a high-altitude engine the Mustang would be suitable for air-to-air combat at the altitudes where combat usually took place in European skies. The turbocharged Rolls Royce Merlin was the ideal candidate, but the entire production of the Merlin-61 was slated for Spitfires.
To increase Merlin production, Rolls Royce contracted with the Packard automobile company in the United States to produce their engines under license. Although famous for its luxury automobiles, Packard had designed and produced the Liberty engine that came into use during the Great War, and which powered U.S.-built aircraft into the 1920s. The first flight by a Merlin-powered British Mustang took place in October 1942. A month later a Mustang powered by a Packard-built Merlin had been produced for the U.S. Army, and it took to the air for the first time.
With the Merlin engine, the Mustang was transformed. Comparisons between Mustangs and Spitfires revealed that the North American design had significantly greater range, while the Mustang’s high-altitude performance had been greatly improved. It was a combination that came about at the right time, as the U.S. Army Air Forces’ experience in Europe had demonstrated the need for a high-performance, long-range fighter.
Converted For Escort Missions
Throughout 1942 and most of 1943, the Mustang fighters sat out the war, although the A-36 and RAF Cooperation versions were seeing combat, particularly in North Africa. But events in Europe were leading toward the further development of the Mustang into the airplane that is so often referred to as the best Allied fighter of the war. By the summer of 1942, the U.S. Eighth Air Force had been waging a steadily mounting strategic bombing campaign against Axis targets in France and the other occupied countries from bases in England. In early 1943, the daylight bombing campaign expanded into German airspace. The B-17 groups that constituted the bulk of VIII Bomber Command strength at the time began taking very heavy losses from German fighter attacks. The Eighth Air Force leadership had gone to war believing that their four-engine Flying Fortresses were properly named, but soon found otherwise when the B-17s began encountering Luftwaffe fighters. Especially heavy losses in the late summer and early fall of 1943 led to the cancellation of further daylight deep- penetration raids into Germany until a long-range escort fighter could be developed.
Throughout 1943, the primary escort fighters available in Europe were RAF Spitfires and USAAF Lockheed P-38 Lightnings and Republic P-47 Thunderbolts. While the P-38 had the range to go all the way to Berlin, the P-47s were limited owing to the higher fuel consumption of their radial engines, and there were not enough available P-38s for the job. All of the P-38s in England had been transferred to North Africa early in the year and were not replaced until late summer, leaving Spitfires as the only escorts available until April, when the first P-47s became operational in the theater. It was not until September that P-38s returned to English skies. Meanwhile, the bombers were left without escorts once they reached the operational range of the Spitfires.
The USAAF engineers at Wright Field in Dayton, Ohio, began looking around for a suitable escort fighter that could be mass-produced in a hurry, and their attention soon settled on the Mustang. The adoption of the Merlin engine had solved the Mustang’s high-altitude performance problems, and the Mustang had been shown to be highly maneuverable, with some restrictions, mainly owing to weight and balance considerations.
Increasing the airplane’s effective range was the primary problem. The Air Corps engineering facilities at Wright Field began working on modifications to increase the Mustang’s fuel capacity and thus increase its effective combat range. Additional fuselage tanks were added to complement the droppable external fuel tanks that had been previously developed for other types.