The Pentagon demanded that China return a U.S. Navy underwater drone captured in international waters in the South China Sea, a confrontation likely to exacerbate tensions in a region where China is asserting greater control and expanding military installations. A Chinese naval ship unlawfully seized the small unmanned vehicle Thursday while the USNS Bowditch, a U.S. Navy survey ship, was collecting it in a routine operation 50 nautical miles northwest of Subic Bay in the Philippines, according to a Defense Department statement.