The P-38J was introduced in August 1943. The turbo-supercharger intercooler system on previous variants had been housed in the leading edges of the wings and had proven vulnerable to combat damage and could burst if the wrong series of controls were mistakenly activated. In the P-38J series, the streamlined engine nacelles of previous Lightnings were changed to fit the intercooler radiator between the oil coolers, forming a "chin" that visually distinguished the J model from its predecessors. While the P-38J used the same V-1710-89/91 engines as the H model, the new core-type intercooler more efficiently lowered intake manifold temperatures and permitted a substantial increase in rated power. The leading edge of the outer wing was fitted with fuel tanks, filling the space formerly occupied by intercooler tunnels, but these were omitted on early P-38J blocks due to limited availability.