“The P-51 Mustang became the decisive weapon in the air war, defeating the enemy fighters deep within their own territory. Many factors were involved in winning the war against the Axis in Europe, but few were as important as the North American P-51 fighter.” – Ray Wagner, author of Mustang Designer
Ed Schmued merged his earlier fighter concepts with a new laminar-flow airfoil to shape the NA-73, as the new plane was designated, and final British approval was given for the purchase of 320 of the planes in that Battle of Britain summer. He spread the design assignment among several of his specialized groups, estimating that one hundred days would be needed to build the first experimental example. The British had required North American to have the plane flight-tested, de-bugged, and in full production within one year, but around the company, serious concerns were surfacing about the new wing and how it might perform. Exhaustive testing, though, soon proved its viability. Schmued’s brilliant scheduling and co-ordination resulted in completion of the first aeroplane by both Engineering and the factory shop in only 102 days, almost exactly as promised.
Forty-four years later, Ed Schmued reflected: “We could never build another plane today in a hundred days as we did then. Today, they just don’t have what it takes. There are too many levels of authority within the [aircraft] companies. We had formed an exception group of engineers with an enthusiasm that was unequalled anywhere. We worked every day until midnight. On Sundays we quit at six p.m., so we knew we had a ‘weekend.’ ”
The NA-73 was a sleek all-metal, stressed-skin airframe, designed to be simple and relatively inexpensive to manufacture. The laminar-flow airfoil produced less drag at high speeds than more conventional airfoils, but also less lift at low speeds, requiring the plane to have larger flaps to keep the landing speed from being too high. The wing had two straight spars and the main landing gear member’s track was nearly twelve feet, making landing easier and safer than in the British Spitfire, for example. All three wheels were fully retractable and the tail wheel was steerable and linked to the rudder. The customer had specified the use of a liquid-cooled inline engine and the Allison V-1710 was the only suitable American-built aero engine available. It was slightly larger than the Rolls-Royce Merlin, a bit lighter, and of similar power at low altitudes. At higher altitudes, however, it could not deliver power like that of the Merlin. The fuel was stored in two self-sealing tanks inboard in the wings. Their combined capacity was 180 U.S. gallons, nearly twice that of the Spitfire.
For armament, the British were requiring two 0.5-inch Browning machine guns in the underside of the nose, synchronized to fire through the propeller arc; two 0.5-inch guns in the wings mounted outboard of the landing gear; and four 0.3-inch guns mounted further outboard on the wings.
North American Aviation had originally been created as a holding company in December 1928. It held interests in several aircraft companies that included Wright Aeronautical, Keystone Aircraft, Travel Air, and the Curtiss aviation companies. The car maker General Motors bought a large interest in North American Aviation in 1933, as well as acquiring General Aviation Corporation. In 1929 it had purchased the controlling interest in Fokker Aircraft Corporation, whose founder, the famed World War One aircraft designer Anthony Fokker, remained as chief engineer.
In 1934, James H. Kindelberger left the employe of Douglas Aircraft where he had served as chief engineer, to head the new North American Aviation, Inc. He brought his long-time friend Leland “Lee” Atwood with him as vice-president to their new factory near Mines Field (now a part of Los Angeles International Airport), Inglewood, California. Kindelberger, too, foresaw the coming war and was familiar with the characteristics and capabilities of the various aircraft likely to be involved when hostilities began. With the opening rounds of the war in Europe, he got hold of RAF combat reports and used them to help develop ideas for new fighter aircraft.
In World War Two, Americans of German birth were often regarded with suspicion by government security officers and, on one occasion, they entered Ed Schmued’s home when he was at work, to look for evidence of Nazi sympathies. His fellow engineers assured them of Ed’s uncompromising commitment to Allied victory and Dutch Kindelberger insisted that Ed and his fellow immigrants were essential to the company’s war effort. Kindelberger had no doubts about their loyalty. Fortunately, German-Americans in California escaped the terrible mass removal and incarceration that befell Japanese-Americans, and were allowed to make their contribution to the Axis defeat.
Unfortunately for the new North American fighter project, the Allison aero engine factory at Indianapolis failed to deliver the power plant for the test aeroplane on time. It would be a further eighteen days before the engine arrived in Los Angeles for test-fitting in the airframe. The delay resulted because the engine was “government-supplied equipment” provided on an “as available” basis. As the NA-73 was, at that point, a private venture, its priority level was far lower than that, for example, of the P-40, another user of the Allison V-1710. Initial engine run tests were conducted on October 11th, followed by the maiden flight of the NA-73X took place on October 26th with veteran test pilot Vance Breese at the controls. While the engine was the same as that powering the Curtiss P-40, Breese found the NA-73X to be 25 mph faster than the P-40.
Flight testing continued until November 20th when the NA test pilot Paul Balfour neglected to switch the fuel valve to ‘reserve’ and ran out of fuel fifteen minutes into a test flight. He was forced to put the precious prototype down on a freshly ploughed field where the wheels dug into the soft ground, causing the plane to flip over onto its back. The pilot was not injured, but the aircraft was badly damaged and required a time-consuming rebuild. Ed Schmued acted swiftly to have the second NA-73 (on the shop floor and scheduled to be the first production aeroplane) prepared for flight test so as not to delay the critical test data gathering.
Even before that first flight of the prototype, the British ordered an additional 300 of the new fighters, for a total buy of 620. In the first recorded reference to the fighter by its nickname, the British purchasing authority called it Mustang in a letter to North American on December 9th.
The U.S. Army Air Corps had the right to block any foreign aircraft sales if it regarded them as not in the Army’s interest. It allowed the sale on the basis that two early examples of the NA-73 be provided to the Army for its own testing and evaluation. It designated these planes as XP-51.
In 1941, RAF Squadron Leader Michael Crossley, who had destroyed nine German planes while flying Hawker Hurricanes in the Battle of Britain, arrived in California to conduct the British acceptance flight tests on the Mustang I, as the RAF now called it. Ed Schmued recalled: “He was a very pleasant Britisher, six feet two inches tall, but the cockpit was designed for a five foot ten inch pilot. When he sat in the Mustang his knees were just about under his chin, but he didn’t complain. After he made his routine flights, which were most satisfactory, he had one more test to do: firing the guns out over the Pacific Ocean. Such gun firing had to have Coast Guard permission, which was a few weeks in coming. The impatient officer said to me: ‘I don’t understand you Americans; we in England just fire into the countryside and you would be surprised how few people get killed.’ ”
By July 1942, all 620 aircraft of the British order were completed, delivered and in service with the Royal Air Force. They were used primarily for photo reconnaissance and low-level cross-Channel sweeps in which they shot up German trains, barges and troop concentrations. Of the Mustangs shipped to England, twelve were lost when the Ocean Venture, a new, California-built British ship, was torpedoed by a German U-boat on February 8th 1942. Eight more Mustangs went down on another freighter that same week.
The first RAF Mustang I destined for delivery in Britain arrived at Liverpool on October 24th 1941. It had been accepted by the RAF in September and arrived without a radio, gunsight, and other equipment that the British intended to provide from their own manufacturers. When that was done the plane went first to Boscombe Down for evaluation by the Aeroplane & Armament Experimental Establishment and then to Duxford for further evaluation by the Air Fighting Development Unit. The Mustangs delivered to the RAF under the original order were equipped with an F-24 camera installation located behind the pilot’s head armour. A second camera for high altitude vertical photography was added later ahead of the tail wheel well.
RAF pilots liked the Mustang and thought it easily the best American fighter. It was faster than the Mk Vb Spitfire up to 25,000 feet and had twice its range, but the Spitfire could go much higher and had better rates of climb and turn, as well as a much better engine in the Rolls-Royce designed Merlin. British tests of a fully-loaded Mustang resulted in a 370 mph top speed at 15,000 feet, a 30,000-foot service ceiling, and a 990-mile range at a cruising speed of 180 mph. Schmued: “A man in the Air Ministry later confessed to me that he had taken our performance guarantee of 370 mph and knocked it down to 300 mph because he supposed that all American plane manufacturers lied about performance. When he found out our quotation was correct, it opened up new possibilities for our plane.”
But the Mustang’s performance rapidly eroded at altitudes above 15,000 feet; its Allison engine being supercharged for best performance at low altitudes. It took the Mustang eleven minutes to climb to 20,000 feet while the Spitfire V could get there in seven. The Spitfire and Germany’s Messerschmitt Bf 109 were both more agile than the Mustang at higher altitudes, and the Mustang weighed roughly a third more than the Spitfire.
The RAF elected to operate the Mustang I in low-level tactical reconnaissance and ground attack roles to take advantage of the plane’s good performance in those situations. It began flying Mustang Is from Gatwick, which is now another major London airport, with the No 26 Squadron in February 1942, and had ten more Mustang squadrons operational by June. Most of them went to work for the Army Cooperation Command replacing the Westland Lysanders and the Curtiss Tomahawks. The first reported aerial victory by the Mustang came when Royal Canadian Air Force volunteer Flying Officer Hollis Hills shot down a Focke Wulf Fw 190 in combat above the British Dieppe commando landings of August 19th 1942. Mustang I performance on combat operations was praised. Its long range, ability to absorb battle damage, and its heavy armament were greatly appreciated in its squadrons as it found and destroyed hundreds of locomotives, barges, and the enemy aircraft on the ground while incurring only a handful of losses in its first eighteen months of operation in Europe.
As a part of the new Lend/Lease Act passed by the U.S. Congress on March 11th 1941, the government was permitted to “lend” American-build aircraft to nations seen as “vital to the security of the United States.” In September the U.S. Army Air Corps ordered 150 Mustangs under Lend/lease for delivery to Britain. The prior British orders for Mustangs had all been direct purchases. These Mustang Ias were equipped with four wing-mounted Hispano cannon. Following the Japanese attack on Pearl Harbor, Hawaii, in December, the army repossessed many of these cannon-equipped Mustangs.
Testing of the two NA-73 (redesignated XP-51 by the U.S. Army) examples at Wright Field in Ohio went slowly. The type lacked the priority given to the Army’s more favoured fighter test programmes, the Republic P-47 Thunderbolt, Bell P-39 Airacobra, and the Lockheed P-38 Lightning also being conducted at Wright. As testing finally progressed, however, the Army pilots wrote positive reports on the plane, but the service issued no orders for its purchase. After a time, the Senate Special Committee to Investigate the National Defense Program, chaired by Missouri senator Harry S. Truman, who would become president of the United States on the death of Franklin D. Roosevelt in April 1945, looked into the matter. It wondered why the Army was reluctant to order the highly regarded North American plane. One theory of the time held that NAA’s Dutch Kindelberger had received demands for bribes in return for a U.S. Army contract and had refused all such demands.
Finally, after the Pearl Harbor attack brought America into the war, the USAAF Chief of Staff General Henry H. Arnold intervened and by April the Army had ordered 500 NA-97 Mustangs for the ground attack role which were redesignated A-36A. This version was to have hydraulic perforated dive brakes meant to keep diving speeds down to 250 mph. The A-36 is remembered as a pretty good dive bomber with the ability to quietly approach a target and strike almost before the enemy was aware of its presence. The plane could start an attack from 10,000 to 12,000 feet, drop its bombs at 3,000 feet and pull out at about 1,500 feet. It handled well and was easily manoeuvrable at treetop level, and it could cope well with battle damage and still bring its pilot home. While not planned as a fighter, the NA A-36 experienced air combat on many occasions and claims for 101 enemy aircraft destroyed in the air were registered by its pilots. A total of 177 A-36s were lost to enemy action.
In April 1942 Rolls-Royce test pilot Ronnie Harker was invited by the RAF to fly the Mustang I up at Duxford near Cambridge. Harker was impressed by the handling and the fuel capacity of the American fighter, as well as the positioning of the guns in the wing, and he reported favourably to the RAF Air Fighting Development Unit on the general performance of the plane. In his report he suggested that a really special fighter might result if this exceptional airframe were to be combined with the well-proven and fuel-efficient R-R Merlin engine. But the report, and his subsequent lobbying of Rolls-Royce officials and key Air Ministry figures, met with little enthusiasm. Very few of them wanted anything to do with an American-built aircraft.
Nonetheless, Harker persisted and was eventually able to convince senior people at the engine maker that his idea of mating the Merlin with the Mustang was not only likely to produce an amazing new weapon against the Nazis, but would also result in a great deal of new engine business for Rolls. R-R then persuaded the RAF to provide three Mustangs for Merlin installation at their Hucknall factory. There followed a series of modifications and minor redesigns which ultimately led to the Merlin 65-powered Mustang Mk X, the highly successful realization of Harker’s inspiration.
Rolls-Royce sent its performance and installation data on the Mk X to North American’s design staff who quickly incorporated the Merlin into production Mustangs.
Thomas ‘Tommy’ Hitchcock, Jr., was the son of an American Racing Hall of Fame horse trainer who had captained the U.S. team in the 1886 inaugural International Polo Cup. Tommy, Jr. joined the Lafayette Flying Corps in France during the First World War. He was shot down and captured by the Germans, but he soon escaped, hid in woods and walked more than 100 miles over eight nights miserable to safety in Switzerland. After the war, he returned to his studies at Harvard, resuming his own polo career and leading the U.S. team to victory in the 1921 International Cup. The energetic, colourful young man for two of F. Scott Fitzgerald’s characters in Tender Is the Night and The Great Gatsby. He returned to the air corps in the Second World War as a Lieutenant Colonel and an assistant air attache at the U.S. Embassy in London. In that capacity Hitchcock flew an early Mustang and, like Harker, enthusiastically urged the further development of the aircraft by cross-breeding it with the Rolls-Royce Merlin 61 engine. It was a recommendation that strongly influenced air force head General Arnold.
In Michigan, Henry Ford was asked to build more Merlin V-12 engines. He declined and agreements were then reached with the Packard Motor Car Company and Continental Motors for the mass production in the United States of the R-R Merlin under license from Rolls-Royce to supplement British production of the power plant. Among many changes necessary for the Merlin-Mustang installation was the move to an enormous four-blade eleven-foot two-inch Hamilton Standard Hydromatic propeller. Packard’s changes included a new carburettor, an automatic supercharger speed shift, water-alcohol injection for emergency power, a new Delco magneto, and a new centrifugal separator to prevent oil foaming. In its part of a reciprocal interchange of information, Packard sent 9,000 drawings to Rolls-Royce during the balance of the war.
Convinced of the promise in the rapidly developing Mustang, General Arnold ordered 2,200 of the Merlin-powered fighters for the U.S. Army Air Force in November 1942. America had been at war with Japan, Germany and Italy since the previous December and North American Aviation was inundated with orders for the AT-6 Texan/Harvard trainer, the B-25 medium bomber, and the Mustang. The company expanded its manufacturing facilities at Inglewood and built new plants in Texas and Oklahoma for Mustang production.
Performance testing of the Merlin-engined Mustangs proved the brilliance of Ronnie Harker’s idea. The fabulous fighter had a top speed of 441 mph, more than 50 mph faster than the Allison-powered Mustang, with greatly improved performance in virtually all other categories as well.
And by late December 1943, the RAF Air Fighting Development Unit had tested the new, improved P-51B Mustang and was impressed. They described it as: “. . . delightfully easy to handle . . . a much cleaner aircraft than the Spitfire Mk IX and twenty to thirty mph faster at all heights, with a range between fifty to seventy-five percent better. Because of its higher wing loading, the Mustang did not climb or turn as quickly as the Spitfire.” When they compared it to a captured Messerschmitt Bf 109G: “The Mustang as faster at all heights and greatly superior in turns . . . while climbing, slightly better above 25,000 feet and worse below 10,000 feet.” All things considered, it was the long-range fighter they had been waiting for.