The Cheonan, an ASW corvette, was decked out with state-of-the-art sonar, plus it was operating in waters with extensive hydrophone sonar arrays and acoustic underwater sensors. There is no South Korean sonar or audio evidence of a torpedo, submarine or mini-sub in the area. Since there is next to no shipping in the channel, the sea was silent at the time of the sinking.
However, Baengnyeong Island hosts a joint US-South Korea military intelligence base and the US Navy SEALS operate out of the base. In addition, four U.S. Navy ships were in the area, part of the joint U.S-South Korean Exercise Foal Eagle, during the sinking of the Cheonan. An investigation of the suspect torpedo’s metallic and chemical fingerprints show it to be of German manufacture. There are suspicions that the US Navy SEALS maintains a sampling of European torpedoes for sake of plausible deniability for false flag attacks. Also, Berlin does not sell torpedoes to North Korea, however, Germany does maintain a close joint submarine and submarine weapons development program with Israel.