The Lockheed P-38 Lightning racked up an impressive series of "firsts"--it was the first Lockheed-designed military aircraft to go into series production, it was the first twin-engined interceptor to serve with the USAAC, it was the first production fighter powered by the Allison V-1710 in-line engine, it was the first modern fighter equipped with a tricycle landing gear, it was the first American plane to use butt-jointed flush riveted external surfaces, it was the first to make extensive use of stainless steel, it was the first fighter to use a bubble canopy right from the start, it was the first fighter with speeds over 400 mph, it was the first US twin-boom fighter to go into production, it was the first USAAF fighter to shoot down a German aircraft, it was the first USAAF fighter to carry out an escort mission to Berlin, it was the first USAAF plane to land in Japan after that country had surrendered, it was the heaviest US single-seat fighter of World War 2, it was the only American fighter in production at the time of Pearl Harbor to be still in production at the war's end, and it accounted for more Japanese aircraft destroyed in combat than any other US fighter.
A total of 10,037 Lockheed Lightnings were built.
Lockheed was invited along with Boeing, Consolidated, Curtiss, Douglas, and Vultee to take part in a USAAC design competition X-608 for a twin-engined high-altitude interceptor. The specification called for a maximum speed of at least 360 mph at 20,000 feet and 290 mph at sea level, an endurance at full throttle of one hour at 20,000 feet, and the ability to take off and land over a 50-foot obstacle within 2200 feet.
The Lockheed design staff was headed by Hall L. Hibbard. Working with Hibbard was the soon-to-be famous Clarence L. "Kelly" Johnson. After studying a lot of different designs, Hibbard and Johnson finally settled on a twin-boom design with each boom extending aft of the engine and the pilot sitting in an enclosed cockpit in a central nacelle. Each boom was to house one of the new 1150 hp Allison V-1710C twelve-cylinder liquid-cooled engine with an exhaust-driven turbosupercharger. The Allison engine at that time had just completed a 150-hour type approval test at 1000 hp. The central nacelle contained a forward-firing armament of one cannon and four 0.50-in machine guns. This armament was quite heavy for its time, the standard USAAC armament of the day being one 0.30-in and one 0.50-in machine guns. One advantage of the twin-boom layout was the possibility of installing the armament in the central nacelle, unhampered by synchronizing gear and allowing sighting of the parallel streams of fire up to the maximum range of 1000 yards. Tail surfaces consisted of a fin and rudder at the end of each boom and a horizontal tailplane and elevator between the booms. It was anticipated that the twin fin-and-rudder tail assembly would increase the effective aspect ratio of the tailplane by the endplate effect, thereby providing stability over a large c.g. range. At 14,800 pounds, the XP-38 weighed more than a bombed-up Bristol Blenheim I, at that time the standard British medium bomber. Fowler flaps were fitted between the ailerons and the booms and between the booms beneath the trailing edge of the wing center section.
The project was given the company designation Model 22-64-01. Lockheed promised a maximum speed of over 400 mph. Although the USAAC was somewhat skeptical about so radical a design, the Model 22 won Design Competition X-608 and on June 23, 1937, Lockheed was awarded a contract for one XP-38 prototype (Ser No 37-457). Construction began in July 1938. Construction proceeded rather rapidly despite the radical features that it embodied. Few problems were presented by the installation of the Allison V-1710-11/15 (C9) engines, which developed 960 hp at 10,000 feet and 1090 hp at 13,200 feet. Each engine had a General Electric B-1 turbosupercharger. To combat torque, the propellers rotated in opposite directions, a special version of the Allison engine being produced with a left-hand rotating propeller shaft. The engines had inwardly-rotating propellers. No armament was installed on the XP-38.
The XP-38 aircraft was completed in December of 1938. On the last day of the year, the completed XP-38 was stripped down, covered with canvas, and loaded onto three trucks. In great secrecy, the convoy of trucks was escorted by police to March Field, near Riverside, California, where Air Corps Project Officer Lt. Benjamin S. Kelsey was to began the flight testing. However, on the very first ground run, the wheel brakes failed and the XP-38 ended up in a ditch. Lt. Kelsey finally took the XP-38 into the air for the first time on January 27, 1939. The early test flights turned up some problems with the wheel brakes and with vibrations of the flaps, requiring that some modifications be made to the prototype. Maximum speed was 413 mph at 20,000 feet, and an altitude of 20,000 feet could be attained in 6.5 minutes. Service ceiling was 38,000 feet. Empty weight was 11,507 lbs, gross weight was 13,964 lbs, and maximum takeoff weight was 15,416 lbs
Reaction to the first few test flights was highly favorable. In spite of the problems encountered on its first few flights, it was decided to attempt a record transcontinental flight before delivering the XP-38 to the Army at Wright Field. At daybreak on February 11, 1939, Ben Kelsey left March Field destined for Mitchell Field, New York with refuelling stops at Amarillo, Texas and Wright Field, Ohio. On the final leg of the flight, the XP-38 lost power as Kelsey was coming in for a landing at Mitchell Field and crashed on a golf course just short of the runway. Fortunately, Lt. Kelsey was unhurt, but the XP-38 was a total loss.