South Korean ships had better be careful.
Hwanghae Province naval base where NLL, NLL facing near Yeonpyeong. Disappeared submersible class, such as three years ago, when the Cheonan destruction of salmon has been known.
30m small, 130-ton torpedo can carry a two-foot Chinese crew of 10 people, and at depths of less than 100m mission for more than three or four days longer available.
“Lost contact” may mean “we sunk them”.
Can’t imagine such a small sub built for North Korea would have technology to evade sonar.