The War Zone article mentions the drones "[having] the capabilities under human control” for phase 1, wonder what they can up with for a communications channel that works underwater. Maybe an acoustic link to some sort of surface vessel/buoy, which can then relay using conventional wireless comms?
Requiring a surface element seems like it would lessen the system's ability to remain undetected. The article doesn't say that undetected observation is the goal, but it seems plausible, because if someone trying to secretly sabatoge the cables sees your observation equipment, you'd think they'd just go find another spot that's not being monitored. I'm guessing it isn't practical to observe the entire length of all cables of interest.