China's large-scale island-building in the South China Sea peaked in the middle of the last decade, when features in the Spratly group such as Mischief, Subi and Fiery Cross reefs were turned into airbase-sized outposts. Construction of that kind then stopped, and the Antelope Reef project is the first significant new artificial island Beijing has begun since 2017. What makes it different from the Spratly outposts is where it sits. Antelope Reef is in the Paracels, closer to the Chinese mainland and to Hainan, inside waters that Chinese naval planners treat as a protected operating area for ballistic missile submarines. A hardened facility with a harbour, a runway and radar coverage there does less to project power into the southern South China Sea and more to secure the northern approaches. Yagong Island, a small feature a short distance to the north-east, is where the sensors appear to be going: the structures photographed there resemble early-warning radar installations already built on other Chinese-held features, and analysts read them as support infrastructure for whatever eventually operates from Antelope Reef.

China claims most of the South China Sea through a broad historic-rights line, overlapping the exclusive economic zones of Vietnam, the Philippines, Malaysia, Brunei and Indonesia. In 2016 an arbitral tribunal constituted under Annexure VII of the United Nations Convention on the Law of the Sea, in a case brought by the Philippines, found that this claim had no basis in the Convention; China rejected the award and has not accepted the tribunal's jurisdiction. A second legal point matters for reclamation specifically: under UNCLOS, artificial islands built on low-tide elevations generate no territorial sea, EEZ or continental shelf of their own, so building them does not create new maritime entitlements even though it creates new military capability. For India the sea matters as a trade artery — a very large share of India's seaborne commerce transits it — and India's stated position has consistently been freedom of navigation and overflight, unimpeded lawful commerce, and resolution of disputes in accordance with UNCLOS.