Japanese Forces Chase Away "Foreign" Sub

ABC News is reporting that Japanese Maritime Self-Defense Forces chased away a submarine from the islands near Okinawa today. The article speculates that the submarine may be Chinese, and that the Japanese P-3 maritime patrol aircraft (MPA) continued to trail the boat. Of all the countries that this submarine is likely to be from, China definitely would be the best suspect. North Korean submarines are unlikely to go that far south, the Russians would be unlikely to get caught by MPAs, and I assume the Americans and South Koreans keep the Japanese fairly well informed about the operating areas of their boats in waters near Japanese territorial waters, due to Prevention of Mutual Interference (link - 12th paragraph) concerns. My initial thought is that this may be a provocation by the Chinese to gauge any Japanese military reaction; on the other hand, the Chinese skipper may have just made a mistake, or suffered some sort of mechanical breakdown. I'll continue to monitor...
Staying at PD...

Update: This BBC article has a little more information, including Chinese reaction. It says the submarine is staying deep, but the Japanese forces are still able to track it. This makes me think that if it is a Chinese nuke boat, it probably does have some sort of mechanical issue; SSNs can normally run faster than Anti-Submarine Warfare (ASW) forces can track...

Going deep...