P-38D “87” of the 1st Pursuit Group during maneuvers in 1941
To establish the P-38 as a fully capable combat aircraft, Lockheed initiated production of the P-38D in August 1941. While externally similar to its predecessors, the P-38D incorporated significant internal improvements based on combat experience. The heavy 37mm cannon was replaced with a 20mm Hispano-Suiza cannon, offering a more practical ammunition capacity of 150 rounds compared to the previous 15. A new gunsight and a gun camera mounted on a modified pylon enhanced targeting accuracy. Self-sealing fuel tanks, a low-pressure oxygen system, and a retractable landing light were also added.
Powered by Allison V-1710-27/29 engines, the P-38D maintained a standard fuel capacity of 210 US gallons but reduced maximum internal fuel capacity to 300 US gallons. Despite this, the majority of the initial production run was designated as training aircraft (RP-38D) and deployed within the US.
Production of the Lightning remained slow, with only 39 aircraft delivered to the USAAF by August 15, 1941. Nevertheless, the P-38 participated in important Army maneuvers in Louisiana that September, contributing to the evaluation of new tactics and equipment. By the time of the Pearl Harbor attack, the USAAF possessed 69 P-38Ds, some of which were hastily assigned to frontline fighter groups.