In April 2015, the U.S. Office of Naval Intelligence confirmed that China has deployed the YJ-18 antiship cruise missile (ASCM) on some People’s Liberation Army (PLA) Navy submarines and surface ships. The YJ-18’s greater range and speed than previous Chinese ASCMs, along with its wide deployment across PLA platforms, would significantly increase China’s antiaccess/area denial capabilities against U.S. Navy surface ships operating in the Western Pacific during a potential conflict. The YJ-18 probably will be widely deployed on China’s indigenously built ASCM-capable submarines and newest surface ships by 2020, and China could develop a variant of the YJ-18 to replace older missiles in its shore-based ASCM arsenal. This paper assesses the capabilities of the YJ-18 and describes the implications of its wide deployment for U.S. forces operating in the Western Pacific. The author exclusively used open source information and considered the capabilities of similar missiles to assess the likely characteristics of the YJ-18.