5-inch/54-caliber Mark 45 gun

Mark 45 5-inch/54-caliber lightweight gun
5-inch/62-caliber Mark 45 Mod 4, in flat-panel gun turret, test firing on USS Forrest Sherman
Type	Naval gun
Place of origin	United States
Service history
In service	1971–present Mod 0: 1971[1] Mod 1: 1980[1] Mod 2: 1988[1] Mod 4: 2000[2]
Used by	See Operators
Production history
Designed	1968[1]
Manufacturer	United Defense[1] (now BAE Systems Land & Armaments)
Produced	1971[1]
Specifications (Mod 2)
Mass	21,691 kg (47,820.5 lb)[1]
Length	8.992 m (29 ft 6.0 in)[3]
Barrel length	6.858 m (22 ft 6.0 in)[3] Rifling: 5.82 m (19 ft 1 in)[3] Mod 4: 7.874 m (25 ft 10.0 in)
Shell	127 × 835 mm .R Conventional: 31.75 kg (70.0 lb)[1]
Caliber	54 caliber
Elevation	−15° to +65°[3] Max. elevation rate: 20°/s[3]
Traverse	±170° from centerline[3] Max. traversing rate: 30°/s[3]
Rate of fire	16–20 rounds per minute automatic[4]
Muzzle velocity	2,500 ft/s (760 m/s)[1] 1,500 ft/s (460 m/s) reduced charge for defilade fire or illumination rounds
Effective firing range	13 nmi (24.1 km)[4] or 20 nmi (37.0 km) (Mod 4)[5]

The 5-inch (127 mm)/54-caliber (Mk 45) lightweight gun is a U.S. naval artillery gun mount consisting of a 5 in (127 mm) L54 Mark 19 gun on the Mark 45 mount.^[1] It was designed and built by United Defense, a company later acquired by BAE Systems Land & Armaments, which continued manufacture.

The latest 62-calibre-long version consists of a longer-barrel L62 Mark 36 gun fitted on the same Mark 45 mount.^[1] The gun is designed for use against surface warships, anti-aircraft and shore bombardment to support amphibious operations.^[1] 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-person crew (gun captain, panel operator, and four ammunition loaders) below deck to keep the gun continuously supplied with ammunition.