The incident tests the waters in the East China Sea after a diplomatic breakthrough between the two countries.


On Thursday, the Japanese Ministry of Defense said that a Chinese frigate and a submarine of unknown origin were both spotted in the contiguous zone around the disputed Senkaku/Diaoyu Islands in the East China Sea. The incident was the first to involve a submarine in the contiguous zone around the Senkakus.

Japan administers the Senkaku/Diaoyu Islands, which China also claims. The Japanese Ministry of Defense did not immediately clarify if the Chinese frigate, which was a Type 054A Jiangkai-II-class frigate, belonged to the People’s Liberation Army-Navy (PLAN) or the China Coast Guard, which uses the Type 054A as well.

“This behavior unilaterally raises tensions, and we are seriously concerned about it,” Defense Minister Itsunori Onodera told the press. Japan’s Chief Cabinet Secretary Yoshihide Suga warned China “not to undermine the trend of improvement in Japan-China relations.”

The two recent incursions come shortly after Japan and China reached a bilateral breakthrough in December 2017 concerning their long-sought East China Sea crisis management hotline. Officials from both sides met in Shanghai for two days and decided to implement the hotline.

The crisis management mechanism, however, excludes Japan’s territorial waters and air space around the disputed Senkaku Islands. It does not include the contiguous zone, where a coastal state is afforded some law enforcement rights under international law. (The contiguous zone is a 12-nautical-mile zone that extends out from the end of the 12-nautical-mile territorial sea.)

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The incident comes just days after four China Coast Guard vessels entered Japanese territorial waters around the disputed islets. While incursions into Japan’s contiguous zone and territorial sea around the Senkakus are fairly common for Chinese maritime law enforcement vessels and civilian fishing trawlers, incursions by Chinese naval vessels are comparatively rarer.

For example, in 2016, for the first time in years, a PLAN frigate entered the contiguous zone of the Senkaku Islands. The vessel in that incident was a Type 054 Jiangkai-I-class ship.

The presence of a submarine during the latest incident adds a new dimension to the fairly regular Chinese incursions into these waters. (Chinese vessels started frequenting the islands in greater numbers following Japan’s 2012 nationalization of the Senkakus.)


Though the Japanese Defense Ministry has not said the submarine was Chinese, the circumstances suggest that it was likely a PLAN vessel. China has probed Japan’s claimed waters and air space in the East China Sea with a range of assets so far, including aircraft, drones, and surface ships. A submarine adds to this growing list. (While this was the first time a submarine entered Japan’s contiguous zone off the Senkakus, a 2004 incident saw a Chinese attack submarine enter Japan’s territorial waters in the region.)