Adding some points: Radio waves (very high frequency) of GPS cannot go deep in the ocean. Very low frequency can, but their wavelenght is very big, so unsuitabl

Adding some points: Radio waves (very high frequency) of GPS cannot go deep in the ocean. Very low frequency can, but their wavelenght is very big, so unsuitable for a GPS. The only ways to "see" undersea are acoustic and magnetic. Nuclear sub navigation rely on inertial systems, and i think they can give a position to civilians for rescue.