In Europe, the P38 had 129,849 sorties for 1758 losses or one loss for every 74 sorties. The P51 flew 213,873 sorties for 2520 losses or one loss every 85 sorties. (the P47 was superior to both in that matter) Some of the reasons for the P38 problems were, as mentioned by other members, engine problems caused by high altitude operations, poor cockpit heating, early P38s had a generator on only one engine so if that engine failed you had to come home on only a battery, the airplane was large and easy to see and identify(an advantage on D-Day), it was a big target and had a lot of critical parts to be hit by enemy fire, it had a very poor initial roll rate,( you can't turn if you can't roll), it's compressibility problems were aggravated because the air temperatures above Europe are colder than in the Pacific or California,(the speed of sound varies only with air temperature) so the pilots could not dive the airplane from high altitudes until it got dive brakes, the pilot work load was high because of twin engines and because of poor cockpit layout,( the fighter conference in 1944 voted the P38L as having the worst cockpit), it was a difficult air plane to maintain. Some pilots said that the P38 had to have two engines so it could come home on one. In the Pacific, the P38 came into it's own(more or less) because of warmer air temperatures and less high altitude fighting and because it's long range was useful in the great distances of the Pacific war. It could wrap up in tight slow speed turns in the hands of an experienced pilot by the use of it's Fowler flaps and because of the contra rotating props taking away the torque problems of a single engined fighter. However Tommy McGuire killed himself maneuvering that way against a Japanese fighter. Energy tactics were really the P38s forte. There were situations in the CBI when the P38 was not appreciated because it used a lot of fuel and every drop of fuel at certain airstrips had to be flown in. The P51 was superior when fuel shortages and primitive maintenance conditions were the norm. On balance it would seem that the P51 was the superior fighter.