Nobody would ever call Thitu Island a Pacific Ocean paradise. The second-largest of the chain of reefs, shoals and atolls in South China Sea known as the Spratly Islands, Thitu is a sunbaked 37-hectare rock, dotted with scruffy trees and long-abandoned military bunkers, eking out existence just a few feet above high tide.

Yet obscure Thitu — known as Pag-asa ("Hope Island") in the Tagalog language of the Filipinos who inhabit it — has become an object of desire in the increasingly contentious geopolitical dispute involving the Philippines, China and four of their Pacific Rim neighbors: Brunei, Malaysia, Taiwan and Vietnam. And, thanks to recent actions by the erratic Philippines President Rodrigo Duterte, the island and its residents are increasingly vulnerable to China's vast ambitions across the entire South China Sea.

Roughly 390 km from Palawan, the westernmost major island in the Philippines, Thitu has three things most of the Spratlys lack: fresh water; a year-round population (roughly 200, including many veterans and schoolchildren); and a crumbling concrete airfield about 1,120 meters long.