CIWS is a close-in weapon system for defense against airborne threats such as anti-ship missiles and helicopters.

191001-N-CL550-0398 WATERS SOUTH OF JAPAN (Oct 1, 2019) A close-in weapon system is fired during a live-fire exercise aboard the Arleigh Burke-class guided-missile destroyer USS Milius (DDG 69). Milius is underway conducting operations in the Indo-Pacific region while assigned to Destroyer Squadron (DESRON) 15, the Navy’s largest forward-deployed DESRON and the U.S. 7th Fleet’s principal surface force. (U.S. Navy photo by Mass Communication Specialist 2nd Class Taylor DiMartino/Released)