01/31/2010. Thirty-six P-38Ds (40-774/40-809) with V-171O¬27/-29 engines differed from the first P-38s in having a low-pressure oxygen system, bullet-proof fuel tanks and retractable landing light. Normal fuel capacity remained 210 gal (795 l) but maximum internal fuel capacity was reduced from 410 to 300 gal (1,552 to 1,136 l). Later these aircraft were redesignated RP-38Ds as combat trainers.