Communicating from buoy to an underwater sub is hard (ULF antennas are 100s of metres long) and more importantly would give away there was a vessel there somewhere.
Also that would only locate where the buoy is, not the sub and the sub probably needs more precise location than that. They want to be able to manoeuvre around underwater terrain features and things.
Comments
Lots of issues with that:
Communicating from buoy to an underwater sub is hard (ULF antennas are 100s of metres long) and more importantly would give away there was a vessel there somewhere.
Also that would only locate where the buoy is, not the sub and the sub probably needs more precise location than that. They want to be able to manoeuvre around underwater terrain features and things.