5&quot;/54 caliber Mark 45 gun5&quot;/54 caliber Mark 45 gun 5"/54 caliber Mark 45 gun The 127 mm (5")/54 caliber (Mk 45) lightweight gun is a U.S. naval artillery gun mount consisting of a 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 127 mm (5")/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 use the  Mark 45 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 gun, but it fires a heavier 127 mm (5-inch) shell which carries a larger burst charge that increases its effectiveness against aircraft. Variants. 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. Guided shell. On 9 May 2014, the U.S. Navy released a request for information (RFI) for a guided 127 mm (5-inch) round that could be fired from Mark 45 guns on Navy destroyers and cruisers. The thinking is that if the technology worked in the Long Range Land Attack Projectile (LRLAP) for the Advanced Gun System on s, it can be applied to a 127 mm (5-inch) mount. This RFI comes six years after the  cancellation 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 . 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 . During 2018 RIMPAC exercises, the 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. 5"/54 caliber Mark 45 gun The 127 mm (5")/54 caliber (Mk 45) lightweight gun is a U.S. naval artillery gun mount consisting of a L54 Mark 19 gun on the Mark 45 mount. It was designed and