Japan's Mainichi Newsreported January 11, 2018 that:
"TOKYO (Kyodo) -- A Chinese frigate and an unidentified foreign submerged submarine were spotted Thursday just outside Japanese territorial waters near the Senkaku Islands [near Miyako Island] in the East China Sea, the Defense Ministry said, prompting Tokyo to protest to Beijing over the sailing..."
PETE'S COMMENT
The Japanese Navy has almost automatically assumed (or decided to announce) that because a Chinese frigate was detected, the submarine must also be Chinese.
My alternative theory is that the Chinese Navy spotted a North Korean (NK) submarine. China wishing to avoid another Cheonan Incident pursued the NK sub to warn-off that sub. The Cheonan Incident was when a NK submarine torpedoed a South Korean surface ship in 2010. An NK sub would also be a threat to Japanese surface ships.
The Chinese frigate's actions is part of China's new policy of pressuring NK to be less belligerent in its actions and threats. China wishes to de-escalate NK vs (South Korea, Japan, US) tensions.
Another conclusion is that Japan is utilising its undersea sensor array to detect NK submarines. See array map below. The array includes seafloor hydrophones and other sensors, which is strung from the Japanese home islands, via Okinawa (main) Island and via Miyako (in Japan's Senkakus) Island etc.
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Pete
"TOKYO (Kyodo) -- A Chinese frigate and an unidentified foreign submerged submarine were spotted Thursday just outside Japanese territorial waters near the Senkaku Islands [near Miyako Island] in the East China Sea, the Defense Ministry said, prompting Tokyo to protest to Beijing over the sailing..."
PETE'S COMMENT
The Japanese Navy has almost automatically assumed (or decided to announce) that because a Chinese frigate was detected, the submarine must also be Chinese.
My alternative theory is that the Chinese Navy spotted a North Korean (NK) submarine. China wishing to avoid another Cheonan Incident pursued the NK sub to warn-off that sub. The Cheonan Incident was when a NK submarine torpedoed a South Korean surface ship in 2010. An NK sub would also be a threat to Japanese surface ships.
The Chinese frigate's actions is part of China's new policy of pressuring NK to be less belligerent in its actions and threats. China wishes to de-escalate NK vs (South Korea, Japan, US) tensions.
Another conclusion is that Japan is utilising its undersea sensor array to detect NK submarines. See array map below. The array includes seafloor hydrophones and other sensors, which is strung from the Japanese home islands, via Okinawa (main) Island and via Miyako (in Japan's Senkakus) Island etc.
The map is from page 54 “Map 4. The US ‘Fish Hook’ Undersea Defense Line” in Desmond Ball and Richard Tanter, The Tools of Owatatsumi Japan’s Ocean Surveillance and Coastal Defence Capabilities (2015, ANU Press) http://press-files.anu.edu.au/downloads/press/p309261/pdf/book.pdf?referer=444. The map may depict past or current locations of the eastern Asia - inner western Pacific SOSUS-IUSS seafloor array.
Pete