The use of a North Korea midget sub to sink a South Korean corvette three months ago, has forced the United States, and South Korea, to seriously confront the problems involved in finding these small subs in coastal waters. This is a difficult task, because the target is small, silent (moving using battery power) and in a complex underwater landscape, that makes sonar less effective. After the Cold War ended in 1991, the U.S. recognized that these coastal operations would become more common. So, in the 1990s, the U.S. developed the Advanced Deployable System (ADS) for detecting non-nuclear submarines in...