in time to support the Allied invasion of France on D-Day. Lockheed production of the Lightning was distinguished by a suffix consisting of a production block number followed by "LO," for example "P-38L-1-LO", while Consolidated-Vultee production was distinguished by a block number followed by "VN," for example "P-38L-5-VN." The P-38L was the first Lightning fitted with zero-length rocket launchers. Seven High Velocity Aircraft Rockets (HVARs) on pylons were placed beneath each wing, and later, five rockets were on each wing on "Christmas tree" launch racks, which added to the aircraft. The P-38L also had strengthened stores pylons to allow carriage of bombs or drop tanks. Lockheed modified 200 P-38J airframes in production to become unarmed F-5B photo-reconnaissance aircraft, while hundreds of other P-38Js and P-38Ls were modified at Lockheed's Dallas Modification Center to become F-5Cs, F-5Es, F-5Fs, or F-5Gs. A few P-38Ls were field modified to become two-seat TP-38L familiarization trainers. During and after June 1948, the remaining J and L variants were designated ZF-38J and ZF-38L, with the "ZF" designator (meaning "obsolete fighter") replacing the "P for Pursuit" category. Late-model Lightnings were delivered unpainted, per USAAF policy established in 1944. At first, field units tried to paint them, since pilots worried about being too visible to the enemy, but the reduction in weight and drag turned out to be a minor advantage in combat. The P-38L-5, the most common subvariant of the P-38L, had a modified cockpit heating system consisting of a plug-socket in the cockpit into which the pilot could plug his heat-suit wire for improved comfort. These Lightnings also received the uprated V-1710-112/113 (F30R/L) engines, and this dramatically lowered the number of engine-failure problems experienced at high altitude so commonly associated with European operations. Pathfinders, night-fighter, and other variants The Lightning was modified for other roles. In addition to the F-4 and F-5 reconnaissance variants, a number of P-38Js and P-38Ls were field modified as formation bombing "pathfinders" or "droopsnoots", fitted with a Norden bombsight or an H2X radar system. Such pathfinders would lead a formation of other P-38s, each loaded with two bombs; the entire formation releasing their ordnance when the pathfinder did. A number of Lightnings were modified as night fighters. Several field or experimental modifications with different equipment fits finally led to the "formal" P-38M night fighter, or Night Lightning. A total of 75 P-38Ls were modified to the Night Lightning configuration, painted flat-black