U.S. Defense Secretary Ash Carter pledged $18 million Sunday to help Vietnam buy U.S. patrol boats, shortly after touring a Vietnamese coast guard vessel that was hit by a Chinese ship during a skirmish in the South China Sea.

Carter, who has been focusing on maritime security during an 11-day trip to the Asia-Pacific, visited the Vietnamese navy headquarters and coast guard headquarters before boarding the ship.

Carter is on his second visit to Asia since becoming defense secretary earlier this year. He said he planned to sign a "vision statement" later Monday with his Vietnamese counterpart to guide the expansion of bilateral military ties.