1971-present
The 5-inch/54 caliber (Mk 45) lightweight gun is a modern U.S. naval artillery gun mount consisting of a 127Â mm (5Â in) L54 Mark 19 gun on the Mark 45 mount.
The gun mount features an automatic loader with a capacity of 20 rounds. These can be fired under full automatic control, taking a little over a minute to exhaust those rounds at maximum fire rate. For sustained use, the gun mount would be occupied by a six-man crew (gun captain, panel operator, and four ammunition loaders) below deck to keep the gun continuously supplied with ammunition.
Development started in the 1960s as a replacement for the 5-inch/54 caliber Mark 42 gun system with a new, lighter, and easier to maintain gun mounting. In United States Navy use, the Mark 45 is used with either the Mk 86 Gun Fire Control System or the Mk 160 Gun Computing System. Since before World War II, 127 mm (5Â inches) has been the standard gun caliber for U.S. Naval ships. Its rate of fire is lower than the British 4.5Â in (114Â mm) gun, but it fires a heavier 127 mm (5-inch) shell which carries a larger burst charge that increases its per-shell effectiveness against aircraft.