No. of Recommendations: 4
That's a torpedo, not a manned object.
Also, "super-cavitating" is loud. Very loud. Which would be detected by (among other things) SOSUS.
The fasted experimental sub was something above 50mph. The Russian Alfa (the fastest sub that saw actual service) was 47mph.
Drag (friction) goes as the square the velocity in a fluid. So you can optimize the drag coefficient (by streamlining the object per the laws of physics), but since you can never get it to zero, the faster you go, the drag is exponential.
A bullet (very streamlined, though not optimized since the back of the bullet is flat, not tapered) will lose all of it's energy in about a meter of water.
