Many things have been said and written about the Mustang - that it was the best combat plane of World War II, that it was the plane that marked the transition from piston-engine fighters to jet fighters, that it was the plane that gave the Allies final supremacy in the skies. The truth is perhaps slightly obscured by all these claims.

The North American P-51 Mustang was the product of two highly advanced technologies: the American aircraft industry, which in 117 days designed a plane body that was extremely advanced in structure and aerodynamics; and the British engine industry, which, with its prestigious Rolls-Royce Merlin, provided the ideal complement. The Mustang would not have become immortal without the British engine, the same engine that had already made the Supermarine Spitfire famous. Beyond this, all is history. A total of 15,686 Mustangs were built. Mustangs destroyed 4,950 enemy aircraft in combat and 4,131 on the ground in the course of 213,873 missions in Europe alone. Mustangs also saw duty during the Korean War, and they served in the air forces of some 20 other countries. A few Mustangs are still flown today.

In April, 1940, the visiting British purchasing commission suggested to North American that they build Curtiss P-40 fighters on license for the RAF. The president of North American, J. H. ("Dutch") Kindelberger, was not enthusiastic. He said his company could produce a combat plane that was better than the

P-40, even using the same engine, the V-12 Allison V-1710. The British accepted Kindelberger's counterproposal, but they made it a condition that the prototype be ready in no more than 120 days because the situation in Europe was extremely serious. Two North American designers, Raymond Rice and Edgar Schmued, got to work at once, and the prototype, the NA-73X, was ready three days ahead of schedule, albeit without an engine and with wheels borrowed from an AT-6 trainer. The first flight took place on October 26, 1940. The plane had exceptionally clean lines, and its performance was outstanding. It flew about 25 m.p.h. faster than the Curtiss P-40.

Meanwhile the U.S. government had approved the RAF order for 320 planes, provided that the USAAC was supplied with two planes for testing. The first production fighter took to the air on May 1, 1941, and remained at North American for technical evaluation. The second reached Great Britain in November and was officially designated the Mustang Mk.l. These planes, which were considered far superior to any other American fighter, were put into service in April, 1942, as tactical reconnaissance planes. About the same time, the British ordered 300 more planes, which differed only in equipment and armament.

Despite its brilliant performance in flight tests with the USAAC, the plane was initially ordered in small quantity (50) for photographic reconnaissance duty. Subsequently, however, an order was placed for 500 planes in a specially designed dive-bomber version, the A-36A. These aircraft were delivered between September, 1942, and March, 1943. Another order was received for 310 P-5lAs, and delivery began in the spring of 1943.

But the Mustang's greatest successes still lay in the future. The idea that led to the Mustang's full development came to British and American technicians almost simultaneously. In Great Britain four Mustangs were given to Rolls-Royce for testing with the Merlin 61 engine. In the United States two bodies were consigned to North American for testing with the Merlin that' the Packard company built on license, the V-1650-3. Thus, in September, 1942, the first P-51B prototype was born. Only minor changes were made in the forward part of the fuselage, to accommodate the new engine. But performance was radically different. Now the plane could reach a speed of 440 m.p.h. at 30,000 feet, and an ascent to 20,000 feet required only five minutes and 54 seconds. This was a remarkable advance over the P-51A's top speed of 390 m.p.h. at 20,000 feet and more than nine minutes in ascent. The plane went into mass production in the summer of 1943. It was built at the Inglewood factory as the P-51B (1,988 aircraft) and in the new Dallas plant as the P-51C (1,750 aircraft). Great Britain received about 1,000 and called them Mustang Mk.III. The first P-51B went into service with the 8th Air Force in England on December 1.

The following spring the main production model appeared, the P-51D. The RAF had experimented with its Mustang Mk.III to improve visibility, and a structureless round hood was introduced, the Malcolm (named after its inventor). North American also tackled the problem. In the P-S1D the rear of the cockpit fairing was removed and a fin was added to the rudder to make up for the loss of lateral surface. The cockpit was given a teardrop-shaped, fully transparent hood. A total of 7,956 Mustangs were built in this model. It was powered by a 1,695-h.p. engine and had a top speed of 437 m.p.h. at 25,000 feet. The fastest Mustang, however, was the final version, the P-51H, which took part in the final operations against the Japanese: 490 m.p.h. at 25,000 feet. A total of 555 Hs were built for use in combat.