The 5"/54 caliber Mark 16 gun (5-inch, 127 mm) was a late World War II–era naval artillery gun mount used by the United States Navy and Japan Maritime Self-Defense Force. These guns, designed specifically for the Montana-class battleships, were to be the replacement for the 5"/38 caliber secondary gun batteries then in widespread use with the US Navy. The ammunition storage for the 5"/54 cal gun was 500 rounds per turret, and the guns could fire at targets nearly 26,000 yd (24 km) away at a 45° angle. At an 85° angle, the guns could hit an aerial target at over 50,000 ft (15,000 m).