In mid-May the South Korean government presented clear evidence, in the form of torpedo remains with North Korean markings, that the north had sunk the southern corvette Cheonan. The torpedo was apparently a North Korean-made acoustic weapon, an example of which the South Koreans had previously recovered. It had seemed unlikely, at least to this author, that the North Koreans would deliberately have sunk a South Korean warship in South Korean waters. Against that, it seems that those using torpedoes often imagine that they are anonymous weapons.
World Naval Developments: North Korea's Gambit
By Norman Friedman