Mate, it's all way beyond my pay grade, but autonomous means just that, think Arthur Clarkes 2001, HAL was autonomous it had a set of directives, and that was that, HAL was in charge.
Just normal wild paranoid guesses but these autonomous drones which could be nuclear powered and be of various sizes depending on missions envisaged, would navigate using topological maps or images of the ocean floor, and quite a substantial data base already exists ...
"... Researchers today published the most detailed map of the ocean floor ever produced. Data collected by satellites and remote sensing instruments were used to created a model at least twice as accurate as previous maps, revealing thousands of previously uncharted seafloor features in the process. And best of all, you can explore the maps for yourself! ..."
http://io9.gizmodo.com/explore-the-worlds-most-detailed-map-of-the-seafloor-r-1642315933
So these drones yet to be created of different sizes and programmed for all sorts of spying and miscelaneous bastardry to inflict on non-cooperative nations would roam the world, resurfacing only to refuel/charge if necessary and update databases and directives and get precise position fixes.
Problemo Uno: The ocean floor data base is incomplete, so we need a fleet of smallish drones to do just that, whilst we still can starting with China, so our Chinese cousins and old allies that they are, want to check what is going on and good on them if that is the case.
