Interesting article, and it seems to answer a lot of issues that were raised here. I was pleased to note that the Navy describes their supersonic bullets, designed to penetrate 12 meters of water as having to “penetrate a steel wall”.
Interesting article…definitely weird science. I don’t think I would have believed it if I hadn’t read it (and we all know that if it’s written it MUST be true 
). Still, I’ll buy the concept for now although I doubt I’ll be on an underwater supersonic transatlantic ‘flight’ in my lifetime.
Check out the link I provided above for a real picture of a supercavity. This one drags behind the foil instead of enclosing it as the supersonic subramine one is supposed to but still interesting.