As any submariner can tell you, it's not possible to use a satellite-based global positioning system (GPS) underwater. The dynamics of underwater acoustics simply do not allow for the constant communication from satellites that GPS requires to perform its calculations. As such, submariners have yet to benefit from the revolutionary advances in navigation that GPS has introduced. That's all about to change.
Engineers working for the US Office of Naval Research have recently filed a patent for a simple way to let submariners utilize GPS positioning. The patent details a system when a base station is tethered to the seabed at a known depth and known GPS location. A bearing calculation is made once a signal is transmitted between submersible and the base station. The GPS station replies with the GPS position, depth, and bearing angle of the request. The submersible then uses its own depth, plus the round-trip pulse time and bearing angle to calculate its own position. It's that simple.
The full patent application for the underwater geopositioning methods and apparatus is located a the US Patent and Trademark office.