Until recently a naval war between Japan and China was not a serious proposition. As recently as the 1980s, China was a “green water” navy barely capable of protecting its own coastline, let alone projecting naval power several hundred miles away. Japan, on the other hand, had a large force of fully modern destroyers tasked with protecting sea lines of communication out to a thousand miles. As long as it stayed clear of the occasional large antiship cruise missile and volleys of unguided torpedoes, the Japanese navy could easily defeat whatever China threw at it.
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