Doesn't cavitation = noise = we know where you are? And add Super to it?
You can't pierce the physical envelope in any way or you lose supercavitation. It's basically a fire and forget projectile of sorts.
They wouldn't be pursuing this, though, if there weren't some technical means available to suppress cavitation noise -- "Prairie Masker" used air bubbles to suppress propeller cavitation, although it didn't do anything for mechanical blade vibration. Streams of air bubbles around the vehicle might be what they're looking at.