The Advanced Gun System (AGS) is a naval artillery system developed and produced by BAE Systems Armaments & Services for the Zumwalt-class destroyer of the United States Navy. Designated the 155 mm/62 (6.1-inch) Mark 51 Advanced Gun System (AGS), it was designed to provide long-range naval gunfire support against shore-based targets. A total of six of the systems were installed, two on each of the three Zumwalt-class ships. The Navy has no plans for additional Zumwalt-class ships, and no plans to deploy AGS on any other ship. AGS can only use ammunition designed specifically for the system. Only one ammunition type was designed, and the Navy halted its procurement in November 2016 due to cost, so the AGS has no ammunition and cannot be used. The Navy planned to remove the AGS from the ships starting in 2023.

The Zumwalt-class destroyer is a class of three United States Navy guided-missile destroyers designed as multi-mission stealth ships with a focus on land attack. The class was designed with a primary role of naval gunfire support and secondary roles of surface warfare and anti-aircraft warfare. The class design emerged from the DD-21 "land attack destroyer" program as "DD(X)" and was intended to take the role of battleships in meeting a congressional mandate for naval fire support. The ship is designed around its two Advanced Gun Systems (AGS), turrets with 920 round magazines, and unique Long Range Land Attack Projectile (LRLAP) ammunition. LRLAP procurement was canceled, rendering the guns unusable, so the Navy re-purposed the ships for surface warfare. Starting in 2023, the Navy will remove the AGS from the ships and replace them with hypersonic missiles.