Armed with little more than flashing lights, loud hailers and water cannons, the Chinese Coast Guard is becoming the vanguard for the country's territorial claims in the South China Sea.

The ostensibly civilian "white-hulled" fleet is a frequent presence in the disputed waters, confronting fishing and coast guard vessels from other claimant nations. By not deploying its gray-hulled navy too visibly, China is seeking to avert international condemnation that might result if it tried to impose its territorial assertions with warships.

That distinction is important as the U.S. has now authorized a navy warship to sail into the 12-nautical-mile zone that China claims around some man-made islands in the South China Sea, according to a U.S. defense official. The question is whether China would use a patrol by a U.S. ship, the first of which began Tuesday morning, as a reason to bring in its navy, a move that would significantly raise tensions in the area.