,,, I'm skeptical that underseas cables are at significant risk from EMPs because of how conductive salt water is. I might be wrong, especially since the US Navy does use VLF to communicate with submarines, but I don't think so. Further, the method the repeaters are powered with are IMO not very vulnerable to EMP because they use ungrounded, symmetrical pairs of wires powered from one end. Power disruptions to that end may cause issues but induced current from an EMP essentially has nowhere to go. It might jump to ground at the far end but the circuit should be well insulated from ground.