Philippine Navy personnel who previously served aboard the BRP Sierra Madre, one of Manila’s most sensitive military outposts in the South China Sea , is under investigation over alleged illegal drug use, sources have told This Week in Asia. The 34-year-old sailor was also involved in resupply missions to and from the grounded warship, which has long served as an Armed Forces of the Philippines outpost at the Second Thomas Shoal, which Manila calls the Ayungin Shoal. One source who tipped off This Week in Asia said the case was being handled quietly by the military as a “national security concern”, given the role of Sierra Madre in Manila’s efforts to maintain its presence at the contested shoal, which Beijing also claims as within its nine-dash line in the South China Sea. The World War II-era tank-landing ship was beached on the shoal in 1999 by the Philippine government in 1999 to assert Manila’s claim, and China has repeatedly demanded its removal. Chinese Coast Guard and Philippine Navy vessels confront each other at the Second Thomas Shoal in the South China Sea on July 20.