The tilted guns in earlier Mustangs experienced frequent jamming problems. To remedy this, the guns in the P-51D were mounted upright.
P-51D Mustang
Gunbay
Tht P-51D's internal armament consisted of three .50-caliber machine guns in each wing. This was a fifty percent increase over the firepower available in the P-51A, -B and -C. They were mounted in a slightly staggered arrangement, and spent shells were ejected through slots under the wing.