Key point: Modern militaries are more reliant on the internet than ever before.
When a July 2015 undersea tremor triggered a rockslide between the islands of Saipan and Tinian in the Northern Marianas Islands, it cut the only fiber-optic cable connecting the archipelago to the global network. Air traffic control grounded flights, automated teller machines shut down, web and phone connections broke.
All the feared impacts of a cyber attack became real for the islanders. A Taiwan-based cable repair ship eventually restored the link, but that was a single break from one natural occurrence. How much more disruption could a deep-sea-faring nation cause its rivals through malicious intent?
Though often mentioned in passing, the fact that the overwhelming bulk of Internet activity travels along submarine cables fails to register with the public. High-flying satellites orbiting the crowded skies, continent-spanning microwave towers and million miles of old 20th Century copper phone wire all carry but a fraction of the Earth's Internet traffic compared with deep-sea fiber-optic cables.
All that buzz occurs in the dark cold parts of inner space and a few very quiet places on land. If you want to tap into that buzz, those quiet places where the sea cables make landfall—from the onshore facilities out to deep-water offshore—are your prized targets. The U.S. has developed exquisite abilities to access underwater things.
One of America's greatest techno-spy capers of the Cold War involved tapping Soviet Navy communications via a submarine cable in the 1970s and 1980s. Before IVY BELLS ended with its unmasking by Soviet spy Ronald Pelton, its clandestine aquanauts, spy sub and nuclear-powered "bug" made espionage history.
If, however, you wish to practice hybrid warfare—disruption and degradation with little overt engagement—then the ability to cut submarine cables at will and at depth gives you a very powerful weapon. Cut up undersea hydrophone networks and you deafen your adversary. Cut Internet cables and you have the ultimate denial-of-service cyber weapon.