The Mark 34 Gun Weapon System (GWS) is a component of the Aegis Combat System that is responsible for controlling and providing fire control to the 5" Mark 45 gun. It is used on the U.S. Navy Arleigh Burke-class destroyer and several later Ticonderoga-class cruisers. The Mk 34 GWS receives target data from the ship's sensors and off-ship sources, performs ballistic calculations, and produces gun control orders. The system is made up of the gun mount itself, the fire-control computer, and an optical sight.

The 5" /54 caliber lightweight gun is a U.S. naval artillery gun mount consisting of a 5 in (127 mm) L54 Mark 19 gun on the Mark 45 mount. It was designed and built by United Defense, a company later acquired by BAE Systems Land & Armaments, which continued manufacture.