The next time the United States sends warships by China's man-made islands in the disputed South China, officers aboard will have to decide how, if at all, they will engage with a pair of giant lighthouses that Beijing lit up there this month.

Chinese officials say the lighthouses on Cuarteron Reef and Johnson South Reef in the disputed Spratly Islands will help maritime search and rescue, navigational security and disaster relief.

Experts, diplomats and foreign naval officers say, however, the lighthouses represent a shrewd move to help buttress China's territorial claims in the South China Sea.