A Chinese Navy survey vessel sailed in the territorial waters of Japan off the coast of Kagoshima Prefecture on the 8th. The survey ship can examine the topography, water depth, and sea temperature of the seabed, and according to a Ministry of Defense official, the Chinese military may be collecting this information to help operate submarines.
International law recognizes the "right of innocent passage" that military ships of each country can pass through the territorial Waters of coastal states as long as they do not harm the order and safety of the coastal states.