Force had converted to the P-51 Mustang. The Eighth Air Force continued to conduct reconnaissance missions using the F-5 variant. Pacific theater The P-38 was used most extensively and successfully in the Pacific Theater, where it proved more suited, combining exceptional range with the reliability of two engines for long missions over water. The P-38 was used in a variety of roles, especially escorting bombers at altitudes of . The P-38 was credited with destroying more Japanese aircraft than any other USAAF fighter. Freezing cockpit temperatures were not a problem at low altitude in the tropics. In fact, the cockpit was often too hot since opening a window while in flight caused buffeting by setting up turbulence through the tailplane. Pilots taking low-altitude assignments often flew stripped down to shorts, tennis shoes, and parachute. While the P-38 could not out-turn the A6M Zero and most other Japanese fighters when flying below , its superior speed coupled with a good rate of climb meant that it could use energy tactics, making multiple high-speed passes at its target. In addition, its tightly grouped guns were even more deadly to lightly armored Japanese warplanes than to German aircraft. The concentrated, parallel stream of bullets allowed aerial victory at much longer distances than fighters carrying wing guns. Dick Bong, the United States' highest-scoring World War II air ace (40 victories in P-38s), flew directly at his targets to ensure he hit them, in some cases flying through the debris of his target (and on one occasion colliding with an enemy aircraft, which was claimed as a "probable" victory). The twin Allison engines performed admirably in the Pacific. General George C. Kenney, commander of the USAAF 5th Air Force operating in New Guinea, could not get enough P-38s; they had become his favorite fighter in November 1942 when one squadron, the 39th Fighter Squadron of the 35th Fighter Group, joined his assorted P-39s and P-40s. The Lightnings established local air superiority with their first combat action on 27 December 1942. Kenney sent repeated requests to Arnold for more P-38s, and was rewarded with occasional shipments, but Europe was a higher priority in Washington. Despite their small force, Lightning pilots began to compete in racking up scores against Japanese aircraft. On 2–4 March 1943, P-38s flew top cover for 5th Air Force and Australian bombers and attack aircraft during the Battle of the Bismarck Sea, in