BAE Systems to rebuild two Mk 45 guns for U.S. Navy warships

The U.S. Navy has added $38.2 million to a BAE Systems contract to overhaul two Mk 45 Mod 4 naval guns, the main deck gun mounted on the Navy’s destroyers and cruisers.

Naval Sea Systems Command issued the cost-plus-incentive-fee modification to an existing contract, funded through fiscal 2024 shipbuilding money that will remain available beyond the current fiscal year. Work will be done at BAE Systems’ facility in Louisville, Kentucky, with completion expected by March 2030.

The Mk 45 is a 127 mm (5-inch), 62-caliber gun that BAE Systems describes as the lightest, most compact and most widely deployed 5-inch naval gun in the world, with more than 260 units delivered to the U.S. Navy and 10 allied navies, including Australia, South Korea, Japan and Denmark. It serves as the primary deck gun on the Navy’s Arleigh Burke-class destroyers and Ticonderoga-class cruisers, handling missions ranging from shore bombardment to surface and limited air defense.

The Mod 4 configuration BAE Systems is overhauling these guns to includes a structurally reinforced mount that increases firing energy by about 50%, letting rounds travel faster and farther, along with a fully digital control system with a touch-screen interface and a lower-maintenance, reduced-signature gun shield. Paired with the Navy’s 5-inch Cargo projectile and an improved propelling charge, the Mod 4 gun can hit targets more than 20 nautical miles (37 km) away.

BAE Systems has steadily won similar Mk 45 overhaul and upgrade work in recent years. In January 2025, the company received a $70 million contract that added funding to a prior $47 million order, with a BAE Systems executive at the time citing Houthi attacks on U.S. Navy ships in the Red Sea as a reminder of why deck-gun firepower matters for self-defense at sea.