The P-38's service record shows mixed results, which may reflect more on its employment than on flaws with the aircraft. The P-38's engine troubles at high altitudes occurred with only the Eighth Air Force. One reason for this was the inadequate cooling systems of the G and H models; the improved P-38 J and L had tremendous success flying out of Italy into Germany at all altitudes. Until the -J-25 variant, P-38s were easily avoided by German fighters because of the lack of dive flaps to counter compressibility in dives. German fighter pilots not wishing to fight would perform the first half of a Split S and continue into steep dives because they knew the Lightnings would be reluctant to follow.