As the P-38H, 600 of these stop-gap Lightnings with an improved 20 mm cannon and a bomb capacity of were produced on one line beginning in May 1943 while the near-definitive P-38J began production on the second line in August 1943. The Eighth Air Force was experiencing high altitude and cold weather issues which, while not unique to the aircraft, were perhaps more severe as the turbo-superchargers upgrading the Allisons were having their own reliability issues making the aircraft more unpopular with senior officers out of the line. This was a situation unduplicated on all other fronts where the commands were clamoring for as many P-38s as they could get. Both the P-38G and P-38H models' performance was restricted by an intercooler system integral to the wing's leading edge which had been designed for the YP-38's less powerful engines. At the higher boost levels, the new engine's charge air temperature would increase above the limits recommended by Allison and would be subject to detonation if operated at high power for extended periods of time. Reliability was not the only issue, either. For example, the reduced power settings required by the P-38H did not allow the maneuvering flap to be used to good advantage at high altitude. All these problems really came to a head in the unplanned P-38H and sped the Lightning's eventual replacement in the Eighth Air Force; fortunately the Fifteenth Air Force were glad to get them.