There's a sub below (Image: Brooke Ocean Technology)From New Scientist:
ROBOTIC submarines have always had trouble when it comes to picking up GPS signals and communicating with their operators. That's because radio signals do not travel far underwater. If the submarines do not surface regularly in order to check their position, they run the risk of drifting off-course.
This problem could now be solved, thanks to a wing-like antenna that piggybacks on small submarines. The antenna ascends to the surface on a tether as and when needed, enabling satellite communications, including GPS readings. It can even carry a camera to serve as a kind of periscope for the sub's controller.
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My Comment: The interesting line in this report is the last one ....
.... the US navy is interested in using autonomous submarines to watch for seaborne attacks ....