More than 2,500 US and Philippine marines joined combat exercises on Monday to be able to respond to any sudden crisis in a region long on tenterhooks over South China Sea territorial disputes and increasing tensions over Taiwan.

The annual military drills are some of the largest so far between the longtime treaty allies under newly elected Philippine President Ferdinand Marcos Jr. His predecessor, Rodrigo Duterte, was an outspoken critic of US security policies and frowned on military exercises with American forces he said could offend China.

Called Kamandag, the Tagalog acronym for “Cooperation of the Warriors of the Sea,” the drills involve 1,900 US Marines and more than 600 mostly Philippine counterparts in mock amphibious assaults and special operations, US and Philippine military officials said.

America’s HIMARS missile launchers and supersonic fighter jets will take part in live-fire maneuvers that will end on October 14, they said. The venues include the western island province of Palawan, which faces the South China Sea, and the northern Philippines, across the Luzon Strait from Taiwan. The military maneuvers are being held simultaneously with combat exercises between US Marines and Japanese army forces on Japan’s Hokkaido involving about 3,000 military personnel from the two sides, US officials said.