Cool. I didn't realize the XP bullet uses the same principles of supercavitation. I had heard about the torpedo, though. It is actually in service with the Russkies- called the VA-111 Shkval. It has a pretty short range, though, and I'm not sure how it is guided. The old versions used inertial guidance and had a nuclear warhead (accuracy by kilotonnage), but the new versions have a conventional warhead. Seems like it would be hard to guide it to hit anything....