5"/54 caliber Mark 45 gun

Mark 45 5-inch/54-caliber lightweight 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 ; 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 (Mod 2)
Mass	21,691 kg (47,820.5 lb)
Length	8.992 m (29 ft 6.0 in)
Barrel length	6.858 m (22 ft 6.0 in); Rifling: 5.82 m (19 ft 1 in) Mod 4: 7.874 m (25 ft 10.0 in);
Shell	127 x 835mm .R ; Conventional: 31.75 kg (70.0 lb)
Caliber	54 caliber
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	2,500 ft/s (760 m/s) ; 1,500 ft/s (460 m/s) reduced charge for defilade fire or illumination rounds;
Effective firing range	13 nmi (24.1 km) or 20 nmi (37.0 km) (Mod 4)

The 5" (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. 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. 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-person crew (gun captain, panel operator, and four ammunition loaders) below deck to keep the gun continuously supplied with ammunition.

History

Development started in the 1960s as a replacement for the 5" (127 mm)/54 caliber Mark 42 gun system that had debuted in 1953 with a new, lighter, and easier-to-maintain gun mounting. The United States Navy uses the Mark 45 with either the Mk 86 Gun Fire Control System or the Mk 34 Gun Weapon System. Since before World War II, 5 inches (127 mm) 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 5-inch (127 mm) shell which carries a larger burst charge that increases its effectiveness against aircraft.

Variants

Mod 2

Mod 4

Mod 0

Used mechanical fuze setter. Two-piece rifled construction, with replaceable liner

Mod 1

Electronic fuze setter replaces the mechanical one. Made with a unitary construction barrel, which has a life span approximately twice that of the Mark 42 gun.

Mod 2

Export version of Mod 1, but now used in the U.S. Navy

Mod 3

Mod 2 gun with a new control system; never put into production

Mod 4

Receives a longer 62-caliber barrel (versus Mod 1 and 2's 54 caliber) for more complete propellant combustion and higher velocity and thus more utility for land attack. Was designed to use the Mark 171 Extended Range Guided Munition (ERGM), which was canceled. The Mk 45 mod 4 uses a modified flat-panel gun turret, designed to reduce its radar signature.

In sustained firing operations (Mode III), the gun is operated by a six-person crew: a gun captain, a panel operator, and four ammunition loaders, all located below decks. In fully automatic non-sustained firing operations (Mode IV), 20 rounds can be fired without any personnel inside the mount, using an automatic loader.

Ammunition

Mark 68 HE-CVT

Weight - 68.5 lb (31.1 kg)
Projectile Length - 26.1 in (66.3 cm)
Used only with Mods 0–2

Mark 80 HE-PD

Weight - 67.6 lb (30.7 kg)
Projectile Length - 26 in (66 cm)

Mark 91 Illum-MT

Weight - 63.9 lb (29.0 kg)
Projectile Length - 26.1 in (66.3 cm)

Mark 116 HE-VT

Weight - 69.7 lb (31.6 kg)
Projectile Length - 26 in (66 cm)

Mark 127 HE-CVT

Weight - 68.6 lb (31.1 kg)
Projectile Length - 26 in (66 cm)

Mark 156 HE-IR

Weight - 69.0 lb (31.3 kg)
Projectile Length - 26 in (66 cm)

Mark 172 HE-ICM (Cargo Round)

Projectile Length - 26 in (66 cm)
Used only with Mod 4

Guided shell

On 9 May 2014, the U.S. Navy released a request for information (RFI) for a guided 5-inch (127 mm) round that could be fired from Mark 45 guns on Navy destroyers and cruisers. This RFI came six years after the cancelation of the Raytheon Extended Range Guided Munition. The shell must have at least double the range of unguided shells for missions including Naval Surface Fire Support (NSFS)/Land Attack, and increasing anti-surface warfare (ASuW) capabilities against fast attack craft (FAC) and fast inshore attack craft (FIAC); the main purpose is to destroy incoming small boats at a greater range with a proximity fuse airburst blast fragmentation warhead to spray shrapnel over swarms.

Expected submissions include the BAE Systems Multi Service–Standard Guided Projectile (MS-SGP), Raytheon Excalibur N5, and OTO Melara Vulcano guided long-range projectile.

Naval Sea Systems Command is also looking to fire a version of the hyper-velocity projectile (HVP) developed for Navy electromagnetic railguns from conventional 5-inch deck guns. Using the HVP could give existing destroyers and cruisers better ability to engage land, air, and missile threats and allow more time to refine the railgun. The HVP would be a cheaper solution to intercepting incoming missiles than a missile interceptor costing hundreds of thousands of dollars. Converting the HVP to fire from conventional guns was not a program of record as of 2015. HVP shells fired from 5-inch deck guns would travel at Mach 3, half the speed of a railgun but twice the speed of conventional rounds. The rounds would be more expensive than unguided shells but cheaper than missile interceptors, and engage air and missile targets out to 10–30 nautical miles (12–35 mi; 19–56 km). During 2018 RIMPAC exercises, the USS Dewey (DDG-105) fired 20 HVPs from a standard Mk 45 deck gun; an HVP shell could cost US$75,000-$100,000, compared to $1-$2 million for missiles.