For the second time in five months, Defense Secretary Ash Carter landed aboard a U.S. aircraft carrier in the bitterly contested South China Sea.

Aboard the USS John C. Stennis, Carter was sending a deliberate message to China on American power with a key U.S. ally by his side: Philippine Defense Secretary Voltaire Gazmin. The two leaders watched U.S. Navy fighter jets launch into the vivid blue skies, about 70 nautical miles west of the island of Luzon.

The U.S. and its allies have complained about China's military build-up in the South China Sea. Beijing has been creating man-made islands, and equipping many with runways, fighter aircraft and other weapons.