As others have noted, Mach 5 with 60,000g means a ~2.4m barrel and ~3ms firing time. That's feasable for low/moderate sea states as any shock to the hull is unlikely to coincide with the instant of firing.
Making the projectiles "smart" is a non-starter. The forces involved in the launch would crush all but the simplest and hardest electronics, would likely bend/break movable fins, and might even detonate the warhead. On top of that, it's going to be enough of a magnetic field (presumably on the order of 1 Tesla, like MRI scanners) to induce enough current to fry electronics and seriously limit the materials that can be used. In addition, it's non-trivial even to steer something at mach 5 - the air has the consistency of a brick wall.
Under-sea blasts work fine for torpedos with a ton of high explosives. This sort of hittile would be maybe 1kg, with a muzzle energy of ~1.5MJ. Water has a specific heat capacity of 4,187J/kgK and a specific latent heat of evaporation of 2,270,000 J/kg. Assuming a sea temperature of 15 deg C it will take over 2.6MJ to boil 1kg of water - in other words, at 100% efficiency of conversion, the KE would be enough to boil only about a pint of sea water, which really isn't going to snap the keel of any ship that wouldn't fit in a bottle.
As an anti-ship weapon, it's going to be limited to perforating the hull and hoping to hit something that'll go "boom". With a decent ROF and a lot of cheap shots, that could still be useful, but it's got to compete with 4.5" guns that can deliver a couple of dozen shells a minute out to 12nmi.
Against Vampires the speed is a significant advantage as it means you can engage further out, which means that any deflection is likely to make the incoming ASM miss the target. While it's possible for a missile to jink to the side to avoid countermeasures, that takes a lot of energy, and it takes a lot of energy to correct the trajectory again afterwards - and so there's a finite limit to what can be done. Of course, you're firing a small, dumb dart a very long way - easy to miss a moving target the size of a phone box at several miles.
Sadly there is one target which this weapon is ideal for use against: the SR-71 'Blackbird' :(