Japan used to be aloof from the three-way chess game of conflicting territorial claims in the South China Sea. Tokyo was pre-occupied with its own territorial dispute with China over a group of uninhabited islands in the East China Sea, known as the Senkaku in Japan and the Daioyu in China.
However, quietly encouraged by the U.S., Japan is moving not so stealthily into a new arena of potential conflict by forging security ties with Vietnam and the Philippines, the two Southeast Asian countries at the fore of territorial disputes with China.
The two nations share claims with Malaysia, Brunei and Taiwan to various reefs and atolls in the South China Sea. Vietnam claims all of the islands in the northern tier, known as the Paracels. Malaysia, Taiwan, Brunei and the Philippines claim specific islands in the southern Spratly group.
Beijing claims them all and has been increasingly aggressive in asserting control, not just with rhetoric but with land-fill and concrete. It is busy turning four reefs and atolls that are barely above water at high tide into artificial islands complete with docking facilities and gun emplacements.
Japan has no territorial claims in the South China Sea, even though several islands were garrisoned by the Imperial Navy during World War II. Additionally, a strict reading of its pacifist constitution limits Japan’s military strictly to the defense of the home islands.