BEIJING — Bitter maritime disputes between China and its neighbors have recently sent fighter jets scrambling, ignited violent protests, and seen angry fishermen thrown in jail. But beneath all the bellicose rhetoric and threatening posture, China also has been waging a quiet campaign — using ancient documents, academic research, maps, and technical data — to bolster its territorial claims.

The frenetic pace of such research — and the official appetite for it — comes after decades of relative quiet in the field and has focused heavily on the two hottest debates: China’s quarrel with six other nations over a potentially oil-rich patch of the South China Sea, and its tense feud with Japan over a small sprinkling of land, which is called the Diaoyu Islands by the Chinese and the Senkaku Islands by the Japanese.