[juiceandjuice]

A submarine can use dynamics and seafloor maps to know where it's at, I think he was alluding to the fact that it's harder for us to know where the submarine is at, and collimate the beam accordingly. Although, if the submarine could collimate the beam it could communicate it's location (which it should be able to know a little bit better than the base) to a base via collimated beam.

Also, you'd probably want at least one more black hole to even attempt a somewhat accurate 2d/3d fix :) I'd imagine VLF communications are probably good enough for now.