The US is said to have a submarine that can cut into undersea cables and install a tap which is no small feet because there is a dangerous high voltage cable to power undersea signal repeaters in them.
they didn't cut the cable but wrapped something around it that got a signal by induction. Works in an electrical cable because the different wires are deliberately wound at varying pitches to minimize crosstalk, but you gotta cut to get into an optic fiber cable. It was a brilliant piece of signals intelligence that was countered by human intelligence, the device is in a museum, one of many in Russia that I'd like to go to but never will.