A U.S. aircraft carrier and two guided missile cruisers are visiting Vietnam in a rare port call that comes as the United States and China increasingly vie for influence in Southeast Asia. The USS Ronald Reagan, along with the guided missile cruisers USS Antietam and USS Robert Smalls, were in Da Nang on Monday for the visit, which is to last through June 30. Neighboring China is Vietnam’s largest trading partner, but Beijing’s sweeping maritime claims in the South China Sea have led to increasing friction with Vietnam, as well as with Malaysia, Brunei, Indonesia and the Philippines. The U.S. has been on a diplomatic push to strengthen economic and military ties in the Indo-Pacific region.