Staff Writer (Updated: 3/20/2016):
The Lightning's twin-boom design was a major departure from most any military-minded aircraft in the skies at the time with most aircraft engineers electing to go the more conventional single-fuselage, monoplane design route. A new United States Army Air Corps (USAAC) specification in 1937 called for an high-level, high-speed interceptor with excellent range. As such, the unique twin-boom design was utilized to provide the power of, not one, but two fully-operating engines. Each engine (spinning three-bladed propellers) would be housed in their own slender "boom" installations complete with turbocharger support for added muscle at high operating altitudes with the single-seat cockpit held in a centralized nacelle between the two booms. Engines were also arranged in a "counter-rotating" fashion meaning that each engine counter-affected the another's inherent torque - negating the "pull" action apparent with single engine designs since the dawn of the piston engine. A short wing surface area - essentially the wing root - connected the booms to the pod-shaped cockpit at the forward end of the aircraft while a broad horizontal elevator plane joined the booms at rear of the aircraft. Part of the specification also called for the fighter to be substantially armed and the P-38 was thusly fitted with a base armament of 1 x 37mm cannon (later downgraded to a 20mm caliber) and a battery of 4 x 12.7mm Browning machine guns, all mounted in the nose. The twin-boom arrangement of the aircraft meant that the nose offered an unfettered vantage point for the pilot so placement of all armament in a single fitting was a logical choice. All said, the revolutionary Lightning was a heavy machine, categorized as a fighter but achieving the same weight class as lighter bombing platforms of her time. The undercarriage was fully retractable and, in another departure from the norm, was of a tricycle arrangement featuring a pair of single-wheeled main legs and a single-wheeled nose landing gear leg.
Overall vision out of the cockpit was rather good although the necessary wing area and forward-held engines blocked some of view. The cockpit sat directly between either engine nacelle and made vision to the lower right or left difficult without banking the entire aircraft. The installation of all armament in the nose, however, provided the pilot with a more accurate attack "cone" when compared to wing-mounted armament common to traditional fighters of the time. The armament was also quite formidable against anything unfortunate to come within the range of the attack cone - machine guns offered up greater rates-of-fire while the cannon could render engines useless with a single direct shot.
When British interest had peaked on the development of the American P-38, several test variants were shipped across the Atlantic for evaluation, sans the superchargers as there remained a ban on American supercharger technology at the time. Thusly the exported P-38 systems woefully under-performed when evaluated by British test pilots and interest in the Lockheed product dissipated. Nevertheless, United States military planners themselves liked what they saw in the P-38 (with the superchargers installed) and would soon be utilizing them across every theater of war around the globe during World War 2. It was soon after production began that the rather forgiving airframe was modified to carry fuel drop tanks to be issued for longer ranges, promoting long distance bombing runs or bomber escort duty and rail-launched rockets (held within structural support "trees" under the wings) could be added, allowing Lightning pilots to field up to 10 x high-explosive, air-to-surface unguided rockets (5 per wing) for use against ground structures, convoy vehicles, concentrations of enemy troops and trains.
The prototype aircraft became the XP-38 which recorded its first flight in January of 1939. On February 11th, 1939, pilot Ben Kelsey completed a coast-to-coast flight that set a new aviation record, completing the feat in just 7 hours and 48 minutes. The ensuing press coverage made the Lockheed P-38 Lightning something of a household name. The only blemish to the feat was the resultant crash landing.
Regardless, development continued in what was already a promising aircraft design amidst rising costs and its inherently complicated technological nature. Thirteen pre-production evaluation aircraft were then delivered as YP-38s with the first one flying on September 16th, 1940 under power from V-1710 series piston engines. These were armed with 1 x 37mm cannon and 4 x 12.7mm heavy machine guns. However, all was not rosey in the P-38s development for there remained a recurring issue encountered along the tail surfaces during high speed dives. It was only later in its development that the issue was ironed out for the better with the introduction of the P-38D and its revised tail section. 36 of the type were produced and these also incorporated self-sealing fuel tanks. The P-38 was therefore formally accepted into service in August of 1940 with serial production of the initial model - the P-38E - beginning in September. At least 210 of this version were delivered by Lockheed and now modified with 1 x 20mm cannon and 4 x 12.7mm heavy machine guns.