Length: 12"
Code: NC10198
In 1939, shortly after World War II began, the British government established a purchasing commission in the United States, headed by Sir Henry Self. Serving along with Sir Wilfrid Freeman, the "Air Member for Development and Production," in 1938, Self was given overall responsibility for Royal Air Force (RAF) production and research and development. He sat on the (British) Air Council Sub-committee on Supply (or "Supply Committee") and one of his many tasks was to organize the manufacture of American fighter aircraft for the RAF. At the time, the choice was very limited; none of the U.S. aircraft already flying met European standards, with only the Curtiss P-40 Tomahawk coming close. The Curtiss-Wright plant was running at capacity, so even that aircraft was in short supply.
North American Aviation (NAA) was already supplying their Harvard trainer to the RAF, but were otherwise underutilized. NAA President "Dutch" Kindelberger approached Self to sell a new medium bomber, the B-25 Mitchell. Instead, Self asked if NAA could manufacture the Tomahawk under license from Curtiss.
Kindelberger replied that NAA could have a better aircraft with the same engine in the air in less time than it would take to set up a production line for the P-40. The Commission set as conditions the fighter be armed with four .303 machine guns, be equipped with the Allison V-1710 liquid-cooled engine, cost no more than $40,000, and stipulated the first production aircraft should be received by January 1941.
The result of the MAP order was the NA-73X project (from March 1940). The design followed the best conventional practice of the era, but included two new features. One was a new NACA-designed laminar flow wing, which was associated with very low drag at high speeds.The other was the use of a new radiator design (one Curtiss had been unable to make work) that used the heated air exiting the radiator as a form of jet thrust in what is referred to as the "Meredith Effect". Because NAA lacked a suitable wind tunnel, it used the GALCIT 10 ft (3.0 m) wind tunnel at Caltech. This led to some controversy over whether the Mustang's cooling system aerodynamics were developed by NAA's engineer Edgar Schmued or by Curtiss, although historians and researchers dismiss the allegation of stolen technology; such claims are likely moot in any event, as NAA had purchased the complete set of P-40 and XP-46 wind tunnel data and flight test reports for US$56,000.
While the United States Army Air Corps could block any sales it considered detrimental or not in the interest of the United States, the NA-73 represented a special case. In order to ensure deliveries were uninterrupted, then-Colonel Oliver P. Echols arranged with the Anglo-French Purchasing Commission to have the RAF get its aircraft in exchange for NAA providing two free examples to the USAAC for evaluation.
The initial placing of the contract was on 24 April. By now the executive head of the British Ministry of Aircraft Production (MAP), Freeman ordered 320 aircraft in March 1940. In September, MAP increased the production order by 300. The prototype NA-73X was rolled in early August, just 117 days after the order was placed, and first flew on 26 October 1940, just 178 days after the order had been placed—an uncommonly short gestation period. In general, the prototype handled well and the internal arrangement allowed for an impressive fuel load. The aircraft’s two-section, semi-monocoque fuselage was constructed entirely of aluminum alloy to save weight. It was armed with four .30 in (7.62 mm) M1919 Browning machine guns in the wings and four .50 in (12.7 mm) M2 Browning machine guns: two in the wings and another two mounted under the engine and firing through the propeller arc using gun synchronizing gear.