Through all the modifications leading from XP-38 to P-38H, the basic contours of the engine nacelles of the Lightning had remained virtually unchanged. The P-38J version, which first began to appear in August of 1943, introduced some appreciable differences in the geometry of the engine nacelles which make this and later versions easily distinguishable from earlier versions of the Lightning.
Earlier P-38s had passed the compressed air from the turbosuperchargers through a hollow passageway lying along the leading edge of the wing all the way from boom to wing tip and back in order to cool it down before it entered the carburetor. There were problems encountered with this arrangement. The difficulty in controlling the superchargers caused frequent engine backfires, some of which actually caused changes in the shape of the wing leading edge. The large area of these wing intercoolers also make them vulnerable to gunfire. The P-38J (known by the Lockheed company as the Model 422) introduced a revised powerplant installation, with the intercooler being changed to a core-type radiator located below the engine. The air intake for the intercooler was sandwiched between the oil radiator intakes in a deeper, lower nose. The core-type radiator took cooling air through the central duct behind the propeller and exhausted it through a controllable exit flap, thus permitting a considerable amount of control over the the temperature of the air entering the carburetor. The leading edge tunnels were eliminated and were replaced by additional self-sealing fuel cells in the outer wing panels.
This modification was initially tested on P-38E Ser No 41-1983. The P-38J also had redesigned Prestone coolant scoops on the tail booms. All P-38Js retained the V-1719-89/91 engines of the P-38Hs, but their more efficient cooling installations enabled military rating at 27,000 feet to be increased from 1240 to 1425 hp, while at that altitude war emergency rating was 1600 hp.
The revised beard radiators produced some additional drag, but it was more than adequately compensated for by the improved cooling which made the Allison finally capable of delivering its full rated power at altitude. Consequently, the P-38J was the fastest variant of the entire Lightning series--420 mph at 26,500 feet. Maximum speed at 5000 feet was 369 mph, 390 mph at 15,000 feet. Range was 475 miles at 339 mph at 25,000 feet, 800 miles at 285 mph at 10,000 feet, and 1175 miles at 195 mph at 10,000 feet. Maximum range was 2260 miles at 186 mph at 10,000 feet with two 250 Imp gall drop tanks. An altitude of 5000 feet could be attained in 2 minutes, 15,000 feet in 5 minutes, 10,000 feet in 7 minutes. Service ceiling was 44,000 feet. Weights were 12,780 lbs empty, 17,500 lbs normal loaded, 21,600 lbs maximum. Wingspan was 52 feet 0 inches, length was 37 feet 10 inches, and height was 9 feet 10 inches. Wing area was 327.5 square feet. Armament consisted of one 20-mm Hispano M2(C) cannon with 150 rounds plus four 0.50-inch Colt-Browning MG 53-2 machine guns with 500 rounds per gun. In addition two 500, 1000, or 1600-lb bombs or ten five-inch rockets could be carried on underwing racks.
The 1010 Model 422-81-14s included three production blocks. The first block consisted of ten service test P-38J-1-LOs. These were quickly followed by 210 P-83J-5-LOs with two 55-US gallon additional fuel tanks in the leading edge space previously occupied by the intercoolers and thus restoring maximum internal fuel capacity to 410 gallons (1010 gallons with drop tanks). Modifications, including the addition of stiffeners, were required to prevent deformation of the new wet wing leading edge. The last production block consisted of 790 P-38J-10-LOs with flat windshields with the bulletproof glass panel being incorporated into the windshield.
These were followed by Model 422-81-22s in two blocks. The first block consisted of 1400 P-38J-15-LOs with revised electrical systems. The second block consisted of 350 P-38J-20-LOs with modified turbo regulators.
When earlier J-series Lightnings went into a high speed dive, their controls would suddenly lock up when a certain speed was reached and the nose would begin to tuck under, making recovery from the dive very difficult. The problem would begin at Mach 0.65 to 0.68, accompanied by vigorous buffeting and a strong nose-down pitch. As speed increased, it became progressively more and more difficult to recover from the dive, larger and larger stick forces being required for a pullout. At Mach 0.72, dive recovery became for all practical purposes impossible, and runaway dives that got this far out of hand usually had fatal results. The onset of severe buffeting would, of course, usually provide adequate warning for a pilot in a diving P-38 that he was about to encounter a problem, but it is easy to get distracted while in the stress of combat. This dive recovery problem was so severe that the Lightnings found it very difficult to follow German fighters in a dive, allowing many Luftwaffe fighters to escape unscathed.
The problem was eventually traced to a shock wave that formed over the wings as the Lightning entered the transonic regime, the shock wave preventing the elevators from operating. In order to counteract this problem, starting with the P-38J-25-LO (Model 422-81-23) production block, a small electrically-operated dive flap was added underneath each wing outboard of the engine nacelles and hinged to the main spar. These dive flaps would change the characteristics of the airflow over the wing, offsetting the formation of the shock wave and permitting the elevators to operate properly. This innovation largely solved the problems encountered by diving P-38s.
The P-38J-25-LO production block also introduced power-boosted ailerons. These consisted of ailerons that were operated by a hydraulically-actuated bell-crank and push-pull rod, making it easier for the pilot to maneuver the airplane at high airspeeds. This boosting system was one of the first applications of powered controls to any fighter, and required only 17 percent of the previous stick forces. The hydraulic aileron booster system vastly improved the roll rate and thereby increased the effectiveness of the P-38 in combat. P-38Js with power-boosted ailerons proved to have the highest roll-rates of any fighter.
210 P-38J-25-LOs were built.
In March of 1944, Colonel Benjamin Kelsey reached an indicated speed of more than 750 mph during a high-speed dive in a P-38, which would have made the P-38 the first supersonic fighter. However, it was later discovered that compressibility effects on the airspeed indicator at about 550 mph had given a greatly exaggerated reading. Nevertheless, the Lightning handled quite well at high speeds, and its strong airframe withstood the excessive aerodynamic loading produced by these high-speed dives.
With the increased use of the Lightning as a light bomber, the type was modified to carry in place of the forward-firing armament either a bombardier with a Norden bombsight in a glazed nose enclosure, or a "Mickey" BTO (Bombing Through Overcast) bombing radar in the nose with an operator station between the radar and the pilot's cockpit. These modifications were developed at the Lockheed Modification Center in Dallas, Texas. These so-called "droop-snoot" Lightnings were used to lead formations of P-38s each carrying two 2000-lb bombs which were released on instructions from the lead bombardier.
Two P-38J-20-LOs (serials 44-23544 and 44-23549) were modified in Australia during the autumn of 1944 for use as single-seat night fighters, carrying AN/APS-4 radar in a pod underneath the starboard wing. These modifications were tested in New Guinea and the Philippines.
A P-38J-5-LO (serial number 42-67104) was tested at Wright Field and Orlando, Florida as an experimental night fighter with a radar operator sitting on a jump seat just aft of the pilot. The AN/APS-4 radar was initially mounted under the fuselage in a pod just aft of the nosewheel. This pod proved to be rather easily damaged by stones thrown up by the nosewheel during takeoffs and landings, so it was repositioned beneath the starboard wing, but this resulted in interference from the adjacent engine nacelle.
Beginning in September of 1944, a P-38J was used to test a unique method for extending the range of escort fighters by having the fighter engage a hook trailed from a B-24H bomber. Attached to the hook was a standard drop tank. After contact, the tank was automatically attached to standard external tank fittings beneath the fighter's wing. The method proved to be basically feasible, but it required considerable skill on the part of the Lightning pilot in order for it to work. Consequently, this innovation was not pursued any further.
A number of P-38Js were modified in service as TP-38J-LO two-seat "piggyback" trainers with a jump seat aft of the pilot. Some of these aircraft carried an AN/APS-4 radar pod underneath the starboard wing and were used to train P-38M crews.
At least one P-38J was successfully flown with skis. P-38J-1-LO Ser No 42-13565 was fitted with an experimental retractable ski installation.
The F-5C-1-LO was the designation given to P-38J airframes converted at the Dallas Modification Center to a standard basically similar to that of the F-5B-1-LO but with improved camera installations. A total of 123 aircraft is believed to have been so modified. The serial numbers of the P-38J aircraft so modified are not known.
A total of 200 P-38J-15-LO fighter airframes were converted in Dallas to F-5E-2-LO reconnaissance configuration. These were produced to a standard similar to that of the F-5C-1-LO. The designation F-5E-3-LO was given to a similar conversion of 205 P-38J-25-LO airframes. Again, any record of the serial numbers of the P-38J aircraft modified to F-5E-2-LO or F-5E-3-LO standards seems to have been lost.
