Subi Reef (Zhubi Reef)

Subi Reef is a Chinese-held military outpost in the Spratly Islands of the South China Sea, built on a reclaimed atoll some 26 km southwest of Philippine-held Thitu Island. It is administered as part of Nansha District of Sansha, Hainan province, and forms one of the three largest Chinese installations in the Spratlys alongside Fiery Cross Reef and Mischief Reef. The Philippines, Taiwan and Vietnam also claim the feature.

The garrison was estimated at around 200 troops in 2014. The outpost supports naval and maritime militia activity in the northern Spratlys, including fishing fleets operating from Hainan; a flotilla of some 30 Chinese fishing vessels was recorded at the atoll in July 2012.

The reclaimed island covers 3.95 square kilometres. A buoyed channel leads through the atoll rim into the lagoon, which is up to 22 m deep and about 3.7 km across, providing sheltered anchorage and harbour works. Wharves line the reclaimed rim. An airstrip of about 3,000 m occupies the northern side of the island, capable of taking large military and civil aircraft; a Hainan Airlines passenger jet conducted a test flight there on 13 July 2016. Other structures include a four-storey building, a weather observation station equipped with Doppler weather radar, and a 55 m lighthouse commissioned in April 2016.

The atoll was naturally exposed only at low tide and carried no permanent installation before China began dredging and land reclamation in 2014. By the end of 2015 the reef had been converted into an artificial island carrying a military base, harbour and runway. On 12 July 2016 the arbitral tribunal in Philippines v. China found Subi Reef to be a low-tide elevation in its natural state, generating no territorial sea, exclusive economic zone or continental shelf.