There were several major changes that set the "D" apart form earlier Mustangs. One was the change from four .50 caliber machine guns to six, three in each wing. Another was to mount the guns upright which helped to eliminate a jamming tendency that occurred in the four gun system. Ammunition was increased to 400 rounds per inboard gun, and 270 rounds for each of the other four. Underwing pylons were strengthened to carry the 110 or 165 gallon auxiliary drop tanks or 1,000 lb bomb. P-51D Mustangs went to fight in the later Korean conflict and it last flew combat in 1956 in the deserts to the Middle East, when Israel used Spitfires, Messerschimitts and Mustangs together in the Mid East conflict.