Widely regarded as the best fighter of the Second World War, the long-range P-51 had a shaky start, but proved to be the key to success in the European strategic bombing campaign.
After the Battle of Britain in 1940, the British needed fighters in a hurry. The RAF had the Spitfire, but there were some production problems and it was feared that they would not be available in large enough numbers. So the English Government contacted the North American Aircraft Company to inquire about obtaining a contract for the factory to build licensed versions of the P-40 Warhawk (at that time the best fighter in the USAAF) for export to the UK. Instead, North American offered to design and produce an entirely new fighter for the British. It was known by the code name NA-73X until the British RAF dubbed it the Mustang.
The prototype was built in less than four months. The Mustang Mark I had twice the range of the Spitfire, and was also faster, at 380mph. The American Allison V-1710 engine, however, had poor performance at high altitude, and the plane also suffered from a slow climb rate. It would not do the job as a bomber escort or interceptor. But the British thought it could do well as a low-altitude fighter and ground-attack aircraft, and the RAF ordered 600 of them. By 1941, fifteen squadrons of British Mustangs were carrying out strafing and bombing attacks on targets in occupied France. The Mustang scored its first air victory while flying with the British during the disastrous raid on the German-held port of Dieppe in August 1942. The Americans, meanwhile, had adopted the P-51 Mustang as well, using 60 of them for low-level photo-reconnaissance.
After the United States entered the war, a strategy of round-the-clock strategic bombing was mapped out that would systematically destroy German industry. But the industrial centers in Germany were some 600 miles away from the airfields in England, too far for any Allied fighter to go. At first, the Americans believed that their heavily-armed B-17s would be able to defend themselves from Luftwaffe fighters using their own defensive fields of machine-gun fire, but during the initial raids in early 1943, losses were so severe that large-scale daylight bombing raids were suspended, and it became obvious that the Allies needed a new fighter that could fly with the bombers and protect them. The new P-47 Thunderbolt was assigned to bomber-escort duty—it was tough and rugged, but, crucially, its huge engine drank fuel at the rate of two gallons a minute, and even with external fuel tanks the fighter only had enough range to stay with the B-17s about halfway before it had to turn back, leaving the bombers unprotected over the targets. What was desperately needed was a fighter that was as maneuverable and powerful as the Nazi Messerchmitts and Focke-Wulfs, but had enough range to defend the bombers through the entire mission.
So, attention turned back to the P-51 Mustang being produced for the English: it had enough range, it was fast, and it was nimble enough to deal with German fighters. What it did not have was sufficient engine power. It was the British RAF who came up with the answer: by replacing the American-built Allison engines with the more powerful British-made Rolls-Royce Merlin, already in heavy production, the Mustang was transformed from a low-altitude ground-attack plane into the premiere fighter of the war. Both the US and Britain began placing orders for Mustangs, and both countries agreed that the Packard Automobile Company in Ohio would be assigned the task of mass-producing American copies of the Merlin engine for use in the P-51. The first Packard-engined Mustang P-51B rolled off the line in November 1942. It could reach 440mph. While the British versions of the P-51 had been fitted with the standard RAF armament of six .303-caliber machine guns, the American models carried four .50-calibers.
The effort culminated in May 1944 when production began on the P-51D model. It had a new bubble canopy which gave the pilot a better view of his surroundings, and a narrower fuselage which increased the speed. Six .50-caliber machine guns in the wing gave it better firepower, and though it was not as maneuverable as the Spitfire, the P-51D’s square-tipped laminar-flow wings allowed it to out-fly anything the Axis could put up against it. And with three internal fuel tanks and two extras under the wings, the Mustang could fly over 2000 miles—enough range to not only reach targets in Germany, but to loiter and fight for a time before running low on fuel. The P-51D changed the air war.
Within a short time, the German Luftwaffe was suffering. The Mustang outclassed both the Me-109 and the Focke-Wulf, and Nazi pilot losses were heavy. By 1944, the Mustangs were facing inexperienced German pilots with little training, and shot them down in droves.
On the way back from escorting a raid, once the bombers had peeled off, the Mustangs were also authorized to use any remaining ammunition on “targets of opportunity” and carried out low-level strafing attacks on German airbases, locomotives, ammo dumps, or road convoys. These proved to be more dangerous than the escort missions: five times as many P-51s were lost to ground fire during strafing than to Luftwaffe fighters during escort missions. But the Mustangs helped to destroy the Nazi logistical system. In the weeks before D-Day, the fighters were unleashed in a wave of ground attacks and sweeps that cut off German reinforcements and supplies. By the time the Allied troops landed in Normandy, the Mustangs and Spitfires had established complete air superiority. P-51s shot down about 5,000 enemy fighters—more than any other Allied fighter.
In the Pacific, the P-51’s long-range was particularly useful. A few P-51A models were deployed to Burma in 1942 where they saw limited action, and in 1943 P-51s began replacing the P-40s in China. But after the island-hopping campaigns of 1943 and 1944, the P-51s found their role. Mustangs based at Iwo Jima and Okinawa were able to fly escort missions for B-29s over Japan, and also carry out raids of their own on isolated Japanese bases and airfields using wing-mounted bombs and rockets.
The final model of the war, the P-51H, was lighter and faster, able to reach 490mph, but the war ended before it could be deployed. Production continued until 1947, and Mustangs saw action during the Korean War as close-support fighter/bombers, often operating from bases in Japan where their longer range allowed them to reach areas that the jet-engined P-80 and P-84 could not. In all, around 15,000 P-51s of various models were produced, with 8,000 of these being the D model. Many Mustangs were sold as “surplus” where they were flown as air racers or as civilian general aviation aircraft.
Because so many P-51s were manufactured during the war, a large number still remain, many of them still airworthy. So nearly every major air museum has a Mustang on display.