There are two types of fluid flows in aero/hydrodynamics, compressible and incompressible.
They can both be modelled by little springs between each fluid particle; when you push against one particle, it pushes against the next via the little interconnecting springs, and the fluid, in effect, compresses.
If you push too fast, the little springs reach maximum compression, and the particles begin to 'pile up' into a bow wave.
For air, this happens at Mach 1, and the air effectively becomes incompressible.
Water is nearly incompressible from the get-go ( also, liquids and solids have transverse 'sound' waves as well as longitudinal ). That's why you see a bow wave on a boat doing 10 mph. That wave is the 'shock' of the particles bunching up because they can't move out of the way fast enough.
Another ( huge ) problem would be cavitation. This is usually seen in pumps/propellers where the fluid can't flow fast enough into the area behind the pump/propeller blades, creating a low pressure area ( or even vacuum ) which tends to destroy equipment.
For a plane the shock is the separation where supersonic air is drastically decelerated to subsonic ( inside the shock cone ), and it carries a lot of momentum/energy which is dissipated in the 'sonic boom'.
If the 'sub' was at a shallow depth, with the surface close by, the spray pattern of the water shock into the air would be extremely interesting. to say the least.
So the shock wave of travelling through water would be no different than through an incompressible fluid such as supersonic air, except for the cavitation problem, which I didn't consider on Sunday ( and which may make this idea a non-starter ).