South Korea and the United States kicked off a combined naval exercise in the East Sea on Monday to reinforce readiness against growing military threats from North Korea, the Navy said. The three-day exercise involved nine vessels and two patrol aircraft from the two sides, including two South Korean submarines, the ROKS Yulgok Yi I destroyer, the USS Shoup Aegis-equipped destroyer and the USS Robert Smalls cruiser, the Navy said. The Navy said the anti-submarine warfare and live-fire drills wer