In February 1937 the US Army Corps issued a specification for a longe range interceptor (pursuit) and escort fighter, calling for a speed of 360 mph at 20,000 ft and endurance at this speed of one hour. Lockheed, which had never built a purely military design, jumped in with both feet and created a revolutionary fighter bristling with innovations and posing considerable technical risks. Powered by two untried Allison engines, with GEC turbochargers recessed into the tops of the tail booms, it had a tricycle landing gear, small central nacelle mounting a 23 mm Madsen cannon and four 0.5 inch Brownings firing parallel directly ahead of the pilot, twin fins, Fowler flaps, cooling radiators on the flanks of the booms and induction intercoolers in the wing leading edges. This box of tricks ran into a ditch on its first taxi test, and two weeks after its first flight undershot the airstrip at Mitchell Field, NY, and was demolished. What made headlines, however, was the fact that it had flown to New York in 7 hr 2 min, with two refuelling stops, demonstrating a performance which in 1939 seemed beyond belief.

The enthusiasm of the Air Corps overcame the doubts and high cost and by 1941 the first YP-38 was being tested, with a 37 mm Oldsmobile cannon, two 0.5in machine gums and two Colt 0.3's. Thirteen YP's were followed on the Burbank line by 20 P-38's, with one 37 mm and four 0.5's plus armour and, in the 36 D models, self-sealing tanks. In March 1940 the British Purchasing Commission had ordered 143 of this type, with the 37 mm Madsen replaced by a 20 mm Hispano and far greater ammunition capacity. The State Department prohibited export of the F2 Allison engine and RAF aircraft, called Lightning I, had early C-15 engines without turbochargers, both having right hand rotation (P-38's had propellors turning outward on each side). The result was poor and the RAF rejected these machines, which were later brought up to US standard. The E model adopted the British name Lightning and the RAF Hispano cannon. Within minutes of the US declaration of war, on 7 December 1941, an E shot down an FW200C Condor near Iceland, and the P-38 was subsequently in the thick of the fighting in North Africa, North West Europe, and the Pacific.

The F was the first to have inner-wing pylons for 1,000 lb bombs, torpedoes, tanks or other stores. By late 1943 new G models were being flown to Europe across the North Atlantic, while in the Pacific 16 aircraft of the 339th Fighter Squadron destroyed Admiral Yamamoto's aircraft 550 miles from their base at Guadalcanal. The J had the intercoolers moved under the engines, thus changing the appearance and providing extra room for 55 extra gallons of fuel in the outer wings. Later J models had hydraulically boosted ailerons, but retained the wheel-type lateral control instead of a stick. The L, with higher war emergency power, could carry 4,000 lb of bombs or ten rockets, and often formations would bomb under the direction of a lead-ship converted to droop-snoot configuration with a bombardier in the nose. Hundreds were built as F-4 or F-5 photographic aircraft, and the M was a two-seat night fighter with ASH radar pod under the nose. LIghtnings towed gliders, operated on skis, acted as fast ambulances (carrying two stretcher cases) and were used for many special ECM missions. Total production was 9,942 and the P-38 made up for slightly inferior manoeuvrability in its range, reliability and multi-role effectiveness.