HANOI—Two U.S. warships this week docked at Cam Ranh Bay, in the first such port call at the Vietnamese naval base since the two countries normalized relations 21 years ago, the U.S. Navy said Tuesday.

Submarine tender USS Frank Cable and guided-missile destroyer USS John S. McCain arrived at the deep-water naval base in Khanh Hoa province on Sunday, in a sign of warming military ties between the two countries.

Cam...