Second Thomas Shoal

Second Thomas Shoal is a submerged reef located in the Spratly Islands, approximately 105 nautical miles west of Palawan, Philippines. It is part of the Kalayaan Island Group, which the Philippines administers as part of Palawan province. The shoal is composed of coral and sand, with depths ranging from 5 to 20 meters, making it unsuitable for permanent structures but strategically valuable as a forward operating base. Its location near the Philippine island of Palawan places it within the Philippines' exclusive economic zone, a claim affirmed by the 2016 Permanent Court of Arbitration ruling. The shoal's proximity to major shipping lanes and potential undersea resources, including hydrocarbons and fisheries, underscores its strategic importance in the South China Sea disputes.

In 1999, the Philippine Navy deliberately grounded the BRP Sierra Madre, a decommissioned tank landing ship, on the shoal to assert territorial claim. The ship has since served as a military outpost, housing a rotating contingent of Filipino marines. The Philippines has periodically resupplied the garrison, but in recent years, Chinese coast guard vessels have blocked these missions, leading to standoffs. In 2024, the two countries reached a temporary agreement to allow resupply of food and water, but tensions remain high. The continued presence of the Sierra Madre is seen as a symbol of Philippine sovereignty, but the aging vessel is deteriorating, raising questions about the future of the occupation.

The 2016 Permanent Court of Arbitration ruling in the Philippines v. China case declared that Second Thomas Shoal is a low-tide elevation, not an island, and thus cannot generate an exclusive economic zone. The ruling also found that China's nine-dash line claim was invalid under UNCLOS. China, however, does not recognize the ruling and continues to assert its claims. The dispute has become a flashpoint in U.S.-China relations, with the United States affirming its mutual defense treaty obligations to the Philippines. In 2024, the U.S. and Philippines conducted joint patrols near the shoal, while China criticized these actions as provocative. The legal status of the shoal remains contested, with no resolution in sight.

Second Thomas Shoal is named after a British survey ship, the HMS Thomas, which charted the area in the 19th century. The shoal is also known as Ayungin Shoal, after the local name for the silver perch fish found in its waters. In 2023, a Chinese coast guard ship fired water cannons at a Philippine resupply boat, injuring Filipino personnel, an incident that drew international condemnation. The shoal is also a nesting site for green sea turtles, which has led to environmental concerns amid military activity. Additionally, the BRP Sierra Madre is one of the oldest ships in the Philippine Navy, having been launched in 1944 as a U.S. Navy LST, making it a relic of World War II.

BRP Sierra Madre

A decommissioned Philippine Navy tank landing ship, grounded on Second Thomas Shoal in 1999 as a military outpost.

Low-tide elevation

A landform that is exposed at low tide but submerged at high tide, which under UNCLOS cannot generate an exclusive economic zone.

Nine-dash line

China's map-based claim to most of the South China Sea, declared invalid by the 2016 PCA ruling.

UNCLOS

United Nations Convention on the Law of the Sea, the international treaty governing maritime boundaries and rights.