They dont have to directly prevent them, just you know, shoot anyone who tries after the fact.

Military is a deterent because of the threat of retalitation, not because they literally prevent other countries from doing things in the moment.

1700km is fuck all. 2 hour flight for commercial airliner, less for pointy aeroplane. even eurocopter can go 300-400 kmh, not a problem

1700km underwater?

The navies of these nations, then.