5-54 Mark 45

Mark 45 5-inch/54-caliber lightweight gun
The latest version, a 5-inch/62 caliber Mark 45 Mod 4 test firing on USS Forrest Sherman in 2007
Type	Naval gun
Place of origin	United States
Service history
In service	1971-present Mod 0: 1971 Mod 1: 1980 Mod 2: 1988 Mod 4: 2000
Used by	See Operators
Production history
Designed	1968
Manufacturer	United Defense (now BAE Systems Land & Armaments)
Produced	1971
Specifications
Weight	Mod 2: 21,691 kg (47,820.5 lb) Mod 4: 28,924 kg (63,766.5 lb)
Length	Mod 2: 8.992 m (29 ft 6.0 in) Mod 4: 10.008 m (32 ft 10.0 in)
Barrel length	Mod 2: 6.858 m (270.0 in) Rifling: 5.82 m (229 in) 8,000 rounds (barrel life) Mod 4: 7.874 m (310.0 in) Rifling: 6.836 m (269.1 in) 7,000 rounds (barrel life)
Shell	Conventional: 31.75 kg (70.0 lb)
Caliber	5.0 inches (127.0 mm)
Barrels	Single barrel (progressive RH parabolic twist)
Elevation	−15° to +65° Max. elevation rate: 20°/s
Traverse	±170° from centerline Max. traversing rate: 30°/s
Rate of fire	16–20 rounds per minute automatic
Muzzle velocity	Mod 2: 2,500 ft/s (762.0 m/s) Mod 4: 2,650 ft/s (807.7 m/s) 1,500 ft/s (457.2 m/s) reduced charge for defilade fire or illumination rounds
Effective firing range	13 nmi (24.1 km)
Feed system	600 rounds (Ticonderoga class) 680 rounds (Arleigh Burke class) 475–500 rounds (other classes)

1971-present

The 5-inch/54 caliber (Mk 45) lightweight gun is a modern U.S. naval artillery gun mount consisting of a 127 mm (5 in) L54 Mark 19 gun on the Mark 45 mount. Originally designed and built by United Defense, it is now manufactured by BAE Systems Land & Armaments after the former was acquired.

The latest 5-inch/62 caliber version consists of a longer barrel L62 Mark 36 gun fitted on the same Mark 45 mount. The gun is designed for use against surface warships, anti-aircraft and shore bombardment to support amphibious operations. 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 (5 inches) has been the standard gun caliber for U.S. Naval ships. Its rate of fire is lower than the British 4.5 in (114 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.

In sustained firing operations (Mode III), the gun is manned by a six-man crew, all located below decks. These are a gun captain, a panel operator, and four ammunition loaders. In fully automatic non-sustained firing operations (Mode IV), the gun can be fired without any personnel inside the mount. However, sustained fire is limited to the capacity of the automatic loader (20 rounds). This means that there will be no one at control panel for the gun to safe the weapon when having to fall back to verbal cease fire to the gun crew.