An aging and rusty Philippine warship run aground in the South China Sea has taken center stage in an increasingly worrisome standoff between Manila and Beijing.

The Philippines’ BRP Sierra Madre has been stranded on a submerged reef known as the Second Thomas Shoal since 1999 — part of an effort to reinforce Manila’s sovereignty over the area as China began a concerted campaign to cement its own claims.

The World War II-era ship was again at the center of tensions between the two Asian countries on Saturday after China Coast Guard ships blocked and deployed water cannons against two Philippine resupply vessels seeking to deliver food and other supplies to military personnel stationed on the vessel.