Standing aboard a United States aircraft carrier, Defense Secretary Ash Carter told U.S. Navy sailors the country plans to “sharpen our military” edge in the Asia-Pacific region during an address Thursday. The announcement came amid China’s further entrenchment there and a multi-national dispute over the South China Sea.

The U.S. “remains the region’s strongest military and security partner of choice,” Carter said while speaking on the USS Carl Vinson in San Diego, CNN reported.

Along with creating military installations in one of the world’s most important and accessible shipping channels, China’s been fighting off the July ruling of a United Nations-backed tribunal that said it did not have absolute autonomy in the South China Sea. China called the Permanent Court of Arbitration’s ruling a “farce” and has tried to tighten its grip on the waterway since 2012, as well as for the better part of four decades.

The U.S., along with main regional ally Japan, is also attempting to expand its presence in the area as it points toward Asia following the passage of the Trans-Pacific Partnership (TPP), a massive 12-nation trade agreement installed to reduce restrictions like tariffs. The South China Sea is responsible for the passage of some 50 percent of the world’s fleet total tonnage.

Carter called Asia “the most consequential region for America’s future.”

Earlier this week, after the U.S. and Japan announced it would conduct military training exercises in the West Pacific, China flew 40 jets over a strait near Japan. A defense ministry spokesman said the Japanese were “playing with fire” by holding the exercises.

Japan responded by scrambling one of its own jets. The country is “determined to defend our land, territorial waters and the skies,” its chief cabinet secretary, Yoshi Suga, said.