US, Philippines Make Defense Commitment in South China Sea Official

The two countries issued new guidelines for the 1951 Mutual Defense Treaty

The US and the Philippines on Wednesday agreed on new guidelines for the 1951 US-Philippine Mutual Defense Treaty that formalize the US commitment to going to war if Philippine vessels come under attack in the South China Sea.

For years now, US officials have pledged to the Philippines that it would intervene in the event of a Chinese attack in the South China Sea. But Philippine President Ferdinand Marcos Jr. came to Washington this week looking to put the commitment in writing.

The guidelines are the first update to the Mutual Defense Treaty since 1951 and specify that the treaty applies to the South China Sea, where China and the Philippines have overlapping territorial claims.

“The guidelines reaffirm that an armed attack in the Pacific, including anywhere in the South China Sea, on either of their public vessels, aircraft, or armed forces – which includes their Coast Guards – would invoke mutual defense commitments under Articles IV and V of the 1951 US-Philippines Mutual Defense Treaty,” the Pentagon said.

The Pentagon said the guidelines also take into account that “threats may arise in several domains – including land, sea, air, space, and cyberspace – and take the form of asymmetric, hybrid, and irregular warfare and gray-zone tactics.” The guidelines “chart a way forward to build interoperability in both conventional and non-conventional domains.”

The new commitments come amid soaring tensions with Beijing in the South China Sea. Ahead of Marcos’ trip to Washington, Chinese and Philippine vessels came close to colliding near Second Thomas Shoal, a Philippine-controlled reef in the South China Sea that is also claimed by China, Taiwan, and Vietnam.

Chinese and Philippine boats often have stand-offs in the disputed waters. The US is considering conducting joint patrols or helping the Philippines resupply a grounded ship it uses as a base on Second Thomas Shoal, which could lead to dangerous encounters between US and Chinese vessels.

The guidelines are the latest in a series of steps the US has taken to boost military ties with the Philippines. Washington and Manila recently signed a deal giving the US access to four more military bases in the Philippines, including three in the north that could be used as staging grounds to fight a war over Taiwan. Last month, the long-time treaty allies conducted their largest-ever joint military exercises.

Author: Dave DeCamp

Dave DeCamp is the news editor of, follow him on Twitter @decampdave.