The atoll measures along its longer southwest-northeast axis, and is up to wide. Its total area including the lagoon and rim of the reef measures, and the lagoon is up to deep. Naturally above water only at low tide, the reef surrounds a lagoon. The People's Republic of China has constructed a 4-story building, a weather observation station with doppler weather radar, wharfs, and a helipad in the area. A buoyed channel guides ships to the inner lagoon which is in diameter. On 12 July 2016, the UNCLOS special arbitral tribunal in the Philippines v. China case confirmed that Subi Reef is, or in its natural condition was, exposed at low tide and submerged at high tide and is, accordingly a low-tide elevation that does not generate entitlement to a territorial sea, exclusive economic zone or continental shelf, but is within 12 miles of a high-tide feature, Sandy Cay on the reefs west of Thitu Island.
The PRC has ratified UNCLOS III; the convention establishes general obligations for safeguarding the marine environment and protecting freedom of scientific research on the high seas, and also creates an innovative legal regime for controlling mineral resource exploitation in deep seabed areas beyond national jurisdiction, through an International Seabed Authority and the Common heritage of mankind principle.
Territorial disputes
The reef is occupied and controlled by China, with a 2014 estimate of 200 troops stationed there, and claimed by Taiwan, the Philippines, and Vietnam. In July 2012, a large fleet of 30 Chinese fishing vessels arrived at the reef from Hainan. In April 2015, a Philippine Navy aircraft patrolling near the reef received "aggressive action" from a Chinese ship. Also in 2015, the USS Lassen sailed within 12 nautical miles, prompting the Chinese Foreign Ministry to call the action a "provocation" and vowed to keep building up in the South China Sea. As per the US Navy, this was a routine "freedom of navigation" exercise. Similar exercises are performed routinely about 12-28 times per year. During 2014, the PRC started reclaiming land at Subi Reef, and by the end of 2015 had developed it into an island of, with a military base, a large harbour, and an airstrip of about. In November 2015, two U.S. B-52 strategic bombers flew in airspace near the area. They were contacted by Chinese ground control, but were allowed to continue their mission undeterred. In April 2016 a new lighthouse 55 metres high commenced operations. A civilian test flight to the new airport was conducted by a passenger jet of Hainan Airlines on July 13, 2016.
