• The Philippines would expect US intervention should China take the BRP Sierra Madre warship.
• The Sierra Madre is a grounded WWII vessel marking Philippine territory in the Second Thomas Shoal.
• Tensions between China and the Philippines are increasingly high in the contested South China Sea.

As pressure builds in the South China Sea amid frequent clashes, the Philippines is drawing a line: should China take a rusted warship outpost marking Manila’s territory, the Philippines would expect US intervention.

Such a move could have significant repercussions, escalating the ongoing Chinese-Philippine dispute in the region into a crisis.

In a new interview with CBS News 60 Minutes, Philippine Secretary of National Defense Gilberto Teodoro explained that there were ongoing discussions between the US and the Philippines about which scenarios amid tensions between Manila and Beijing would prompt America to get involved.

One flash point, Teodoro said, would be if China took the BRP Sierra Madre, a grounded, rusted warship that marks sovereign Philippine territory. “If China were to take the Sierra Madre, that is a clear act of war on a Philippine vessel,” he said.

The Sierra Madre, a World War II-era LST-542-class tank landing ship that belonged to the US Navy and later Vietnam before it was transferred to the Philippines. The vessel was intentionally grounded by the Philippines on the Second Thomas Shoal to serve as a marker for Philippine maritime territory. The Philippines maintains a small garrison of marines on the ship.

“That is an outpost of Philippine sovereignty,” Teodoro explained. “So we’re not talking about a rusty, old vessel solely. We’re talking about a piece of Philippine territory.”

China has repeatedly targeted resupply missions for the outpost. For instance, in June, Chinese vessels and crews armed with bladed weapons raided Philippine ships near the Sierra Madre. The incident followed earlier clashes in which China rammed vessels or hit them with water cannons. These tense encounters have continued, raising concerns.

The US and the Philippines have a mutual defense pact, meaning if one is attacked, the other would come to its aid. The incidents so far, while troubling, have fallen short of this expectation.

But the possibility of US involvement remains. Just last month, for example, US Indo-Pacific Command commander Adm. Samuel Paparo said that US vessels could escort Philippine ships on resupply missions to the Sierra Madre, calling that “an entirely reasonable option” within the treaty.

China claims sovereignty over a majority of the South China Sea, even though its claims are not recognized by international law. Over the past few years, China has increased its efforts to assert its authority in the region, bringing it into conflict with the Philippines. Manila says that Beijing’s behavior violates its exclusive economic zone.

China’s moves against the Philippines also come against the backdrop of larger tensions in the Indo-Pacific region. Other US allies and partners have accused Beijing of violating their airspace and waters or recklessly harassing their aircraft operating in international airspace.