My father was a submariner. (Score 4, Interesting)

I've asked him about how powerful the sonar was and to give you an idea how dangerous it is he told me about some standard submarine procedure. Basically, if a submarine comes under threat from enemy frogmen or divers, the defence the sub has is to turn the active sonar on and start pinging. If a diver is underwater and within a couple hundred yards, he will die from the intensity of the sound under water. In other words the sonar is VERY powerful. Trust me a 200db blast will likely give someone a very bad day if they are near by.