The Republic of Korea Navy's Aegis destroyer Yulgok Yi I, front row right, U.S. Navy's aircraft carrier USS Nimitz, center, Japan Maritime Self-Defense Force's Umigiri, front row left, travel in formation during a joint naval exercise in international waters off South Korea's southern Jeju Island, April 4. The South Korean, U.S. and Japanese navies began their first anti-submarine drills in six months the previous day to boost their coordination against increasing North Korean threats. Courtesy of South Korea's Ministry of National Defense |