The seas may soon have high-precision positioning systems of their own, however, through a DARPA program aimed at providing US Navy submersibles with a new means of navigating the ocean's depths.
The radio signals broadcast by orbiting GPS satellites reach all corners of the globe, but are brought to a halt at the water's surface. While this is obviously problematic if you carry out most of your business beneath the seas, underwater vehicles can partially solve this problem by coming up to the surface every so often.
The trouble is, this increases the chances of detection when operating in hostile environments, and considering that enemies might jam the signal anyhow, it could be a dangerous exercise in futility.
So DARPA has enlisted the services of BAE Systems to develop a system that will allow for GPS-like precision while underwater. The program is called the Positioning System for Deep Ocean Navigation (POSYDON) and, if all goes to plan, will allow the navy's submersibles to remain concealed by the ocean while accurately navigating.