>That said, a sub at missile launch depth is susceptible to a hypersonic weapon from above.
If you know where it is. If you do, the sub has already failed as a weapons system. We have all sorts of weapons that can take out subs if we know where they are.
> That said, a sub at missile launch depth is susceptible to a hypersonic weapon from above
The point of subs is that you don't know where they are. That's why we have them in the first place.
That said, a sub at missile launch depth is susceptible to a hypersonic weapon from above. With sufficient mass, even a kinetic only impact from the surface could take out those subs. A nuclear depth charge can take out subs down to their crush depth although I don't know if you could deliver it on a hypersonic glider.
The defense for this stuff is lasers of course. An interesting technical weakness of hypersonic devices is that they are on the edge of their energy/drag limits (they are already struggling to travel through the soup of the atmosphere at those speeds). If you can ablate their leading edge with a laser to change their drag profile they may self destruct through atmospheric friction.