U.S. Navy USS Mustin Destroyer Fires Mk 45 Gun Proving Indo-Pacific Combat Readiness.

The U.S. Navy Arleigh Burke class destroyer USS Mustin fired its 5-inch Mk 45 Mod 4 naval gun during a live-fire drill in the Western Pacific, demonstrating its ability to deliver precise and sustained surface fire in contested waters, as reported on April 16, 2026. The event highlights a core combat function for forward-deployed ships, reinforcing their role in sea control, close-range engagements, and deterrence against regional threats.

The firing validated the ship’s main gun system as a reliable tool for naval surface fire support and rapid-response engagements against maritime or coastal targets. It also signals restored combat readiness as Mustin reenters frontline operations in the Indo-Pacific, reflecting the U.S. Navy’s emphasis on maintaining high-tempo, forward-based firepower in a region defined by growing naval competition.

Related topic: U.S. Navy Deploys Upgraded USS Mustin Destroyer to Japan to Reinforce Indo-Pacific Missile Defense.

USS Mustin (DDG 89) fires its Mk 45 Mod 4 5-inch naval gun during a live-fire exercise in the Western Pacific, demonstrating the destroyer's close-range sea control, naval gunfire support, and forward-deployed combat readiness with U.S. 7th Fleet (Picture source: U.S. DoW).

The Mk 45 Mod 4 is a fully automatic 127mm naval gun designed to engage surface, air, and land targets, while providing an Arleigh Burke-class destroyer with an immediately available fire option below the threshold for missile employment. In scenarios where a commander must warn, disable, suppress, or support forces ashore without expending vertical-launch missiles, the 5-inch gun remains a tactically flexible tool.

On DDG 89, the relevant configuration is the 5-inch/62-caliber Mk 45 Mod 4, fitted to DDG 51-class destroyers from DDG 81 onward. The longer 62-caliber barrel, strengthened gun and mount subsystems, improved control architecture, and reduced-signature gun shield distinguish it from earlier 5-inch/54 mounts and increase its relevance for naval surface fire support. BAE Systems states that the Mod 4 can reach more than 20 nautical miles with the Navy’s 5-inch Cargo projectile and improved propelling charge, while the U.S. Navy lists a 13-nautical-mile range with conventional ammunition.

The gun mount includes a 20-round automatic loader drum and can fire 16 to 20 rounds per minute from that ready supply, allowing the ship to place a short, intense volume of fire on a surface contact or shore target. Normal operation is remote, through the Mk 160 Gun Computer System or Mk 86 Gun Fire Control System, with the crew positioned below deck, reducing exposure and preserving combat endurance during sustained operations. Destroyers carry a 600-round conventional magazine, giving the gun a persistence advantage that missiles cannot match in lower-intensity engagements.

A live-fire exercise of this type verifies far more than whether a round leaves the barrel. It tests the destroyer’s fire-control chain, ammunition handling procedures, loading rhythm, safety discipline, mount response, recoil management, communications between the bridge and combat information center, and the crew’s ability to transition from routine watchstanding to weapons employment. For a forward-deployed warship, these drills are a readiness currency: the weapon must be reliable, but the crew must also be fast, deliberate, and confident under pressure.

The Mk 45 gives Mustin a scalable response against fast surface craft, hostile small boats, exposed coastal positions, and time-sensitive surface contacts inside gun range. It can support visit, board, search, and seizure operations by providing overwatch, and it can deliver suppressive fires in support of amphibious or special operations forces operating near the littorals. This kind of gun capability complements, rather than replaces, long-range missiles by filling the gap between small-caliber defensive weapons and high-value precision weapons.

The exercise also matters because the Western Pacific is a theater where geography compresses reaction time. Narrow seas, island chains, dense commercial traffic, and heavily monitored approaches create conditions in which destroyers may need to demonstrate resolve without immediately escalating to missile engagements. A 5-inch gun firing drill signals that Mustin’s crew can employ proportional force, sustain presence, and defend the ship in close-range encounters where seconds and rules of engagement matter.

Mustin’s broader combat value comes from the combination of the Mk 45 gun, the Aegis Weapon System, Mk 41 Vertical Launching System, Standard Missile family, Tomahawk cruise missiles, Vertical Launch ASROC, torpedoes, close-in defenses, and embarked MH-60R helicopters associated with Flight IIA destroyers. Arleigh Burke-class destroyers are multi-mission surface combatants able to conduct anti-air warfare, anti-submarine warfare, anti-surface warfare, strike missions, and, on equipped ships, ballistic missile defense.

That mix makes the Mk 45 tactically important despite the destroyer’s missile-heavy design. Missiles give Mustin reach, but the gun gives it endurance and immediacy. In a maritime security patrol, the ship can fire warning shots or disabling fire; in a surface action scenario, it can engage contacts that do not justify a missile; in a littoral fight, it can suppress coastal threats or support forces operating ashore. This layered armament is central to the operational logic of Indo-Pacific naval deterrence.

The exercise also reinforces the role of DESRON 15, which is responsible for the readiness, tactical, and administrative control of nine forward-deployed Arleigh Burke-class guided-missile destroyers and serves as the principal surface force of Battle Force Seventh Fleet in the Western Pacific and Indian Oceans. For allied navies operating with U.S. forces, a destroyer that can integrate Aegis sensors, missile defense, anti-submarine warfare, and naval gunfire support improves interoperability across combined patrols, carrier strike group operations, and crisis-response missions.

The key point is that this was not a routine photo opportunity: a 5-inch live-fire event on a newly returned forward-deployed destroyer demonstrates combat-system revalidation, crew recertification, and theater deterrence at the same time. In a region where U.S. naval forces must reassure allies, contest coercive behavior, and preserve freedom of maneuver, Mustin’s Mk 45 Mod 4 remains a practical weapon: fast enough for tactical response, powerful enough for surface and shore effects, and sustainable enough for prolonged presence operations.