A super cavitating object in seawater (how to get things to go fast underwater) is within an air bubble so its actual speed is somewhere around the speed of sound in air, depending on pressure.
The bubble is created by diverting a fraction of the exhaust through the tip of the object. Russia has some torpedo type weapons that do this and is probably what did in the Kursk (one lighting off inside). It’s aimed fire though, not currently maneuverable IIRC...
The best idea I’ve heard with respect to those is to put them in concrete submarines that sit on the bottom and fire at passing targets.
VA-111 Shkval
https://en.wikipedia.org/wiki/VA-111_Shkval
“...speeds in excess of 200 knots (370 km/h or 230 miles/h)...”
Not even close to “Speed of Sound” (in air or water)