5"/54 caliber Mark 45 gun

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

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.

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

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

Receives a longer 62-caliber barrel (versus Mod 1 and 2's 54 caliber) for more complete propellant combustion and higher velocity[6] 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.

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 155 mm (6 in) Long Range Land Attack Projectile (LRLAP) for the Advanced Gun System on Zumwalt-class destroyers, it can be applied to a 127 mm (5-inch) mount. This RFI comes 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.[7][8]

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.[9] 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.[10] 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).[11] 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.[12]

 Australia

• Royal Australian Navy
  • Anzac-class frigate: Mod 4 (upgraded from Mod 2)
  • Hobart-class destroyer: Mod 4

 Denmark

• Royal Danish Navy
  • Absalon-class frigate: Mod 2

 Greece

• Hellenic Navy
  • Hydra-class frigate (MEKO 200 HN)

 Japan

• Japan Maritime Self-Defense Force
  • Mogami-class frigate: Mod 4
  • Atago-class destroyer: Mod 4
  • Maya-class destroyer: Mod 4
  • Akizuki-class destroyer: Mod 4
  • Asahi-class destroyer: Mod 4

 South Korea

• Republic of Korea Navy
  • Sejong the Great-class destroyer: Mod 4
  • Chungmugong Yi Sun-sin-class destroyer: Mod 4
  • Incheon-class frigate: Mod 4

 New Zealand

• Royal New Zealand Navy
  • Anzac-class frigate: Mod 2

 Spain

• Spanish Navy
  • Álvaro de Bazán-class frigate: Mod 2

 Taiwan

• Republic of China Navy
  • Kee Lung-class destroyer

 Thailand

• Royal Thai Navy
  • Naresuan-class frigate: Mod 2 (being upgraded to Mod 4)

 Turkey

• Turkish Navy
  • Barbaros-class frigate (MEKO 200 TN II)
  • Yavuz-class frigate (MEKO 200 TN I)

 United States

• United States Navy
  • Active service ships:
    • Ticonderoga-class cruiser: Mod 2[4]
      • CG-52-73: Mod 4 after receiving the cruiser modernization
    • Arleigh Burke-class destroyer:
      • DDG 51–80: Mod 2[4]
      • DDG 81–112: Mod 4[4]
  • Decommissioned:
    • California-class cruiser
    • Kidd-class cruiser
    • Spruance-class destroyer
    • Tarawa-class amphibious assault ship (later removed)
    • Virginia-class cruiser

 Australia

• Royal Australian Navy
  • Hunter-class frigate: 9 ships ordered[13]

 United Kingdom

• Royal Navy
  • Type 26 frigate: 8 ships ordered, 3 in build (Mod 4)

 Turkey

• Turkish Navy
  • TF2000-class frigate: 7 in planned

• Otobreda 127/54 Compact and Otobreda 127/64: contemporary 127 mm naval gun from Italian manufacturer Oto Melara
• 4.5 inch Mark 8 naval gun: contemporary standard naval gun for British ships
• AK-130: contemporary 130 mm twin standard naval gun mounting for Russian ships
• H/PJ-38 130mm naval gun : contemporary 130 mm standard naval gun mounting for Chinese ships
• French 100 mm naval gun: contemporary standard naval gun for French ships