Tensions are soaring, but Southeast Asian nations are struggling to push back on Beijing’s contested claims and tap the energy resources their growing economies need.

A U.S. Navy amphibious ship, a French frigate and a pair of Philippine vessels have kicked off the at-sea portion of a joint-force exercise taking place throughout the Philippines this month.

The United States and the Philippines kicked off their most extensive joint military exercise ever on Monday, with drills scheduled in the tense South China Sea amid warnings from China over its territorial claims.

The vast energy riches of the South China Sea have long been eyed by the Philippines and Vietnam as a way to reduce their reliance on imported gas and oil. But an armada of Chinese fishing boats and coast guard vessels— including “The Monster”—are blocking their way.

American and Filipino forces launched their largest combat exercises in years Monday in a show of allied firepower that has alarmed Beijing.

The Philippines is strengthening its relationship with its oldest treaty ally, the United States. The two nations share a complex, close relationship dating to the late 1800s.

The Philippine Navy has set sail for 10 days of exercises with ships from the U.S. and France amid heightened tensions with China in the region.