This has major implications in how the USN will operate manned/unmanned assets. The oceans are vast and deep and knowing the precise location of one's assets at any point in time is a major advantage.
https://defensesystems.com/articles/2017/02/14/darpauuv.aspx
DARPA Discovers "GPS-Like" undersea drone connectivity
The Pentagon’s research entity and BAE Systems are working together to develop a next-generation undersea drone communications technology to help identify mines, find enemy submarines and surveil many items relevant to combat missions.
Using underwater acoustic signals, a surface buoy, beacon or “node,” and GPS signals in a coordinated fashion, the Positioning System for Deep Ocean Navigation (POSYDON) is able to quickly relay location coordinates from undersea drones on patrol to command and control systems on board a ship or submarine.
The program, now in a Phase I developmental effort, is a collaborative enterprise between industry and the Defense Advanced Research Projects Agency (DARPA).
POSYDON provides “omnipresent, robust positioning across ocean basins. By ranging to a small number of long-range acoustic sources, an undersea platform would be able to obtain continuous, accurate positioning without surfacing for a GPS fix,” DARPA developers explained.
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