Which kind? 'Hypersonic' is a speed regime, not a technology in itself.
Hypersonic cruise missiles are not in the purview of ballistic missile defense, unless they have a ballistic stage, in which case they might be. Hypersonic boost-glide vehicles, having a ballistic boost-stage, are countered by some forms of ballistic missile defense, but not all.
Ballistic missile defense is a defense against ballistic missiles. Not torpedoes, cruise missiles, artillery shells, nukes smuggled in shipping containers, frogmen going up a river with a SDV, or anything else. Pretty much just ballistic missiles, or at least weapons with a ballistic boost stage.
I was responding to this, specifically, but did not elaborate enough:
"in North Dakota, they would need to use their own ballistic missiles for it"
There are a lot more ways to fly a nuclear weapon to North Dakota than just ballistic trajectories. Bombers, cruise missiles, hypersonic missiles, etc.
Russia can barely maintain the gear they have that costs orders of magnitude less than a hypersonic missile / nuclear torpedo. Whats the chances their hypersonic missiles / nuclear torpedos even work?.
I wouldn't make any decisions on the thought that they won't work. Even if 90% of their currently deployed nukes don't work, that's still 160 deployed nukes that work, which is enough (not for outright extinction, but still). And 90% would be a high estimate given that Russia is genuinely very capable at rocket tech.
Hypersonic cruise missiles are not in the purview of ballistic missile defense, unless they have a ballistic stage, in which case they might be. Hypersonic boost-glide vehicles, having a ballistic boost-stage, are countered by some forms of ballistic missile defense, but not all.
Ballistic missile defense is a defense against ballistic missiles. Not torpedoes, cruise missiles, artillery shells, nukes smuggled in shipping containers, frogmen going up a river with a SDV, or anything else. Pretty much just ballistic missiles, or at least weapons with a ballistic boost stage.