The U.S. Navy said aircraft carrier operations in the South China Sea are part of its routine presence in the Indo-Pacific region.

China has sent two aircraft carriers into the Pacific for joint military drills, signaling a bold new chapter in its naval ambitions. Japanese Defense Minister Gen Nakatani confirmed the exercises began Saturday and said Monday that the carriers were observed launching and recovering jet fighters to the east of Iwo Jima.

The transformation of the derelict Soviet carrier Varyag into the Liaoning showcased China’s growing shipbuilding expertise—and its determination to build indigenous naval capabilities.