The Sierra Madre is a Philippine Navy ship that was grounded on the Second Thomas Shoal in the Spratley Islands to serve as a make-shift outpost in the ongoing sovereignty dispute. It has been reported that the ship is close to falling apart, China is trying to prevent the Philippines from supplying the site with construction materials and the speculation is that China will try to occupy the shoal if and when the Sierra Madre breaks up or otherwise becomes inhabitable.

Marines here is understood to include any Filipino armed forces personnel