On March 11, 1939, the USAAC Materiel Division called for a new type of twin-engined, high-performance interceptor fighter. The successful entry was, however, to derive as many design features as possible from already existing aircraft. The Lockheed entry was a progressive development of the P-38 Lightning, and was given the company designation of Model 222. The Model 222 had the same general arrangement as the P-38, but featured a pressure cabin and was powered by a pair of turbosupercharged twenty-four cylinder Pratt & Whitney X-1800-SA2-G (military designation XH-2600) liquid-cooled engines which were supposed to develop somewhere between 2000 and 2200 horsepower. Lockheed proposed to replace these engines by a pair of 2300 hp Wright R-2160 Tornado turbosupercharged radials in production aircraft. Armament was to be a pair of 20-mm cannon and four 0.50-inch machine guns. Total fuel capacity was to be 300 US gallons, as compared to 230 US gallons for the early production P-38. The Model 222 was rather optimistically estimated to have a top speed of 473 mph at 20,000 feet when powered by the Pratt & Whitney XH-2600s, and a speed of no less than 500 mph at the same altitude when powered by the Wright Tornadoes.
A contract for a single XP-49 prototype was officially issued on January 8, 1940. Because the Lockheed company was preoccupied with the P-38 Lightning, work on the XP-49 proceeded quite slowly during the early months of 1940. Both the USAAC and Lockheed soon came to realize that with either the Pratt & Whitney XH-2600 or the Wright R-2160 engines, the XP-49 would be seriously overpowered.
On January 1, 1943, the XP-49 was damaged during an emergency landing at Muroc AAB after a simultaneous inflight failure of both the hydraulic and the electrical systems.. By that time, the Army had lost all interest in the XP-49, since the performance was actually inferior to that of the standard P-38G which was already in service. In addition, the questionable future of the troublesome Continental engine caused the Army to abandon any further consideration of quantity production of the XP-49.
However, things changed quickly at that point. As combat experience with the P-38 in Russia grew, calls were mounting for the troublesome liquid-cooled engine installation to be replaced by a radial engine. This would ease operations from the crude Russian airfields as well as reducing maintenance. Initially, Lockheed examined installing a pair of Wright R-2600-12 Cyclones rated at 1,700 horsepower but those engines proved to be unsuited to turbocharging. The alternative was to use a pair of Pratt & Whitney R-2800-9 Double Wasp engines rated at 2,000 horsepower. This was the option selected.
The problem was that, while the depth of the R-2800 was compatible with the existing boom structure, the engine’s width was 20 inches greater and that could not be easily accommodated. At that point, somebody remembered the XP-49 sitting out on an airfield somewhere. The booms there had been designed to accommodate much larger engines and could be modified to include the R-2800.
The result was the XP-49A, an aircraft that was effectively a hybrid of the proposed XP-38H and the XP-49. The weight of the XP-49 was reduced by deletion of the pressurized cockpit and the elaborate cooling system used for the liquid-cooled engines. The XP-49A proved to have sparkling flying capabilities, exhibiting a clear improvement over the P-38, able to "fly rings around the Lightning" in the words of one pilot. The only problem was an outbreak of minor but troublesome fuel leakage problems that were eventually solved. At that point the XP-49A was ordered into production.
Variants
Lockheed P-49B Lightning
The P-49B was virtually identical to the P-49A except for the installation of a low-pressure oxygen system. Production deliveries started to US-based units in October 1943 with the type reaching the Russian Front in January 1944.
