"The Mk 38 Mod 4 Machine Gun System (MGS) is an upgrade … to address deficiencies in meeting Counter Unmanned Aerial Systems (C-UAS) requirements," the Navy has said.
What the Mk 38 Mod 4 actually is
The Mk 38 Mod 4 is a new point-defense configuration installed on the Arleigh Burke class destroyer USS Mustin that pairs a 30mm Mk 44 Mod 3 Bushmaster II chain gun with a .50 caliber M2 machine gun mounted on top — a visibly "piggy-backed" arrangement. The complete system includes a separately mounted Mk 48 Mod 2 electro‑optical sight system (EOSS) and a Mk 134 Mod 0 operator console for remote operation. The Mod 4’s Mk 44 gun offers selectable single-shot, burst, and two full‑auto settings (100 and 200 rounds per minute), while the M2 fires at around 500 rounds per minute. The system is also designed for integration with the Aegis Combat System on Arleigh Burke destroyers.
How the Mod 4 fits into the Mk 38 family
The Mod 4 departs from earlier Mk 38 variants in significant ways. The original Mk 38 Mod 0 was a manually operated, deck‑mounted 25mm M242 Bushmaster developed in the late 1970s. The Mod 1 entered serial production in the late 1980s. After the 2000 attack on USS Cole, the Navy acquired Mk 38 Mod 2 (the Typhoon Weapon System) with remote control, mount stabilization, an electro‑optical/infrared sensor and laser rangefinder, and ammunition‑handling improvements. The Mod 3, acquired in the 2010s, added a faster 7.62x51mm Mk 52 Mod 0 chain gun feeding from a 750‑round magazine and an improved EO/IR sensor capable of 330‑degree surveillance that is decoupled from the gun. By contrast, the Mod 4 is a Navy designation for a Seahawk DS30 series derivative from MSI Defense Systems centered on the 30mm Mk 44 and the piggy‑backed M2.
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End the scrambleTesting, deployment, and current fleet status
The Navy reports a July 2022 test in which a Mk 38 Mod 4 system "successfully identified, tracked and engaged both surface and aerial targets using live ammunition against fixed and moving targets," highlighting an "enhanced fire‑control chain" and the 30mm gun’s improved performance. USS Mustin received its Mod 4 in 2024 and, as of the latest imagery released by Destroyer Squadron 15, remains the first — and apparently the only — U.S. Navy warship fitted with this upgrade. DESRON 15 released photographs showing Mustin replenishing at sea and images from live‑fire training in the Indian Ocean in August 2026. The Navy signed a contract with MSI Defense Systems for an initial low‑rate production batch of 15 systems in 2023, and Naval Sea Systems Command said in February that Naval Surface Warfare Center Dahlgren Division is finalizing configuration work so the system "can be introduced to a wider set of platforms as fleet requirements evolve."
Integration with Aegis and the implications for counter‑drone defense
One distinguishing feature of the Mod 4 is its design for Aegis integration on Arleigh Burke destroyers. The separate Mk 48 Mod 2 optical turret appears to replace an older EOSS previously mounted atop the bridge. The Navy noted that radar targeting through Aegis would be a "big advancement" for some target types, like drones, even as the public imagery and descriptions leave specifics — for example, magazine capacities for each gun — unclear. The Mod 4 sits inside a broader push to harden short‑range ship defenses: the Navy is equipping more destroyers with anti‑drone interceptors, planning to replace Phalanx CIWS on Arleigh Burke variants with RIM‑116 Rolling Airframe Missile launchers, and investing in laser and high‑power microwave directed‑energy systems, physical interceptors, and electronic warfare tools. The Navy cited lessons from ongoing operations with Iran, actions in and around the Red Sea, and observations from the war in Ukraine as drivers underscoring the need for additional layers of protection against uncrewed and small‑boat threats.
What this means for the Navy, the U.S. Coast Guard, and MSI Defense Systems
- The Navy: The 2027 fiscal year budget request makes clear the plan is to integrate the Mk 38 Mod 4 on all Flight IIA and Flight III Arleigh Burke subvariants. Meanwhile, all remaining Mk 38 Mod 2s in service are being upgraded to Mod 3.
- The U.S. Coast Guard: Future Coast Guard icebreakers — which will use Aegis‑derived combat systems — are slated to feature the Mk 38 Mod 4 as part of their design, extending the configuration beyond Navy surface combatants.
- MSI Defense Systems and suppliers: MSI’s Seahawk lineage already sees international use; the 2023 low‑rate production contract for 15 systems binds MSI into U.S. naval modernization plans while NAVSEA and NSWC Dahlgren finalize broader integration work.
USS Mustin functions as the Navy’s visible field test for a Mod 4 that combines increased lethality, layered calibers, and tighter combat‑system integration. The public record shows successful tests, a small initial production buy and a multiyear plan to expand the fit on specific destroyer flights and Coast Guard icebreakers — but also leaves concrete technical details, like magazine capacities and the exact sensor‑to‑turret targeting workflow, unreported. Whether the Mod 4 becomes a common deckhouse sight across the fleet now depends on the NAVSEA configuration finalization, production follow‑through, and how well the system performs in operational settings beyond training ranges.
