...where Earth has expected an invasion from the evil Posleen for a long time. They knew in advance that they could not count on satellites surviving more than the first few seconds of the battle. So they developed other technologies for positioning:

1) A sort of gps structured around transponders implanted in the earth.
2) Computers that take fixes from those transponders when in range and always attempt to keep track of their own motions (via inertia sensors) to estimate position when out of range.
3) An enhanced tercom-like facility based on an embedded terrain model. (I think it's called tercom, right? terrain modeling and navigating for cruise missiles?)

Did not talk about navigation at sea (yet), but there's no reason you could not implant transponders on the sea floor.

Oh, the novel is "Gust Front". Second in a series. Pretty good military SF. Though the author expects you to keep track of a prohibitive (for me) number of characters.