5-inch/54-caliber Mark 16 gun

The 5"/54 caliber Mark 16 gun (spoken "five-inch-fifty-four-caliber") was a late World War II–era naval gun mount used by the United States Navy, and later, the Japan Maritime Self-Defense Force. These guns, designed originally for the Montana-class battleships and then the abortive CL-154-class cruisers, were to be the replacement for the 5"/38 caliber secondary gun batteries then in widespread use with the US Navy.

Design
The 5"/54 cal gun turrets were similar to the 5"/38 caliber gun mounts in that they were equally adept in an anti-aircraft role and for damaging smaller ships, but differed in that they weighed more, fired heavier rounds of ammunition, and resulted in faster crew fatigue than the 5"/38 cal. guns.

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 away at a 45° angle. At an 85° angle, the guns could hit an aerial target at over 50,000 ft.

The cancellations of the Montana-class battleships in 1943 and then the CL-154 class cruisers in 1945 pushed back the first use of the 5"/54 cal guns to their installation aboard the US Navy's Midway-class aircraft carriers. The guns proved adequate for the carrier's air defense, but were gradually phased out of use by the carrier fleet because of their weight (rather than having the carrier defend itself by gunnery the task would be assigned to other surrounding ships within a carrier battle group). These mounts were then installed in the Japanese Akizuki-class destroyer (1959) and Murasame-class destroyer (1958) destroyers in 1958–59.