China’s disruptive progress in the field of anti-access and area denial is driving a profound shift in U.S. force structure and planning in the Asia-Pacific. At the heart of Washington’s military “pivot” toward Asia is a revolutionary new concept: AirSea Battle. This brief examines the future role of the Indian Ocean in the event of a Sino-U.S. conflict. It contends that the world’s third largest body of water, hitherto largely ignored, will morph from a peripheral flank to the Western Pacific Theater of Operations to form the wider front of AirSea Battle.