The 5-inch/54 caliber Mark 45 is a naval gun system used by the United States Navy and other allied forces. It features a 5-inch diameter barrel and is designed for both surface and air targets. The "54 caliber" refers to the length of the barrel, which is 54 times the diameter of the bore, enhancing its range and accuracy. This gun system is capable of firing various types of ammunition, including guided projectiles, making it versatile for different combat scenarios. It is typically mounted on destroyers and cruisers, providing essential fire support for naval operations.