Reading the article, it seems the real use case (unmentioned) is on ballistic missile nuclear subs. You want them to be well below the surface of the water, wh

Reading the article, it seems the real use case (unmentioned) is on ballistic missile nuclear subs. You want them to be well below the surface of the water, where the GPS signal does not penetrate so well. Thus having a way for them to know precisely where they are without relying on GPS would be very helpful.