5-inch/54-caliber Mark 45 gun

[1] It was designed and built by United Defense, a company later acquired by BAE Systems Land & Armaments, which continued manufacture.

[1] The gun is designed for use against surface warships, anti-aircraft and shore bombardment to support amphibious operations.

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.

[8][9] 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.

[12] 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.

Map with 5-inch/54-caliber Mark 45 operators in blue
Mod 2 gun aboard Australian Anzac -class frigate HMAS Arunta
Loading a 70-pound (32 kg) 5-inch round in the below-deck gun mount