Protecting Undersea Internet Cables: A Tech Challenge

When the lights went out on the BCS East-West Interlink fiber optic cable connecting Lithuania and Sweden on 17 November, the biggest question wasn’t when internet service would be restored. (That’d come another 10 or so days later.) The outage—alongside a cable failure the next day of an undersea line connecting Finland and Germany—soon became a whodunit, as German, Swedish, and Finnish officials variously hinted that the damage to the lines could constitute acts of “sabotage” or “hybrid warfare.” Suspicion soon centered around Russia or China—especially given the presence of a Chinese-flagged cargo vessel in the area during both incidents.

The outages underscore how much of the global communications and financial system hinges on a few hundred cables of bundled glass fibers that are strung across ocean floors around the world, each cable about the same diameter as a garden hose. And, says Bryan Clark, a senior fellow at the Washington, D.C.-based Hudson Institute, defending undersea fiber optic cables from damage and sabotage is increasingly challenging. The technology to do so is nowhere near bulletproof, he says, yet the steep cost of failing to protect them is too high to consider simply writing them off. (NATO is currently investigating future internet backup routes through satellites in the case of undersea cable failures. But that technology is only in a preliminary, proof-of-concept stage and may be many years from real-world relevance.)

“In the past, when these kinds of cable cutting incidents have happened, the perpetrator has tried to somehow disguise the source of the disruption, and China’s not necessarily doing that here,” Clark says. “What we’re seeing now is that maybe countries are doing this more overtly. And then also they may be using specialized equipment to do it rather than dragging an anchor.”

Clark says protecting undersea cables in the Baltic is actually one of the less-challenging situations on the geostrategic map of seafloor cable vulnerabilities. “In the Mediterranean and the Baltic, the transit lanes or the distance you have to patrol is not that long,” he says. “And so there are some systems being developed that would just patrol those cables using uncrewed vehicles.”

In other words, while the idea of uncrewed underwater vehicles (UUVs) regularly patrolling internet cableways is still in the realm of science fiction, it’s not that far removed from science fact as to be out of the realm of soon-to-be-realized possibility.

But then comes the lion’s share of the undersea internet cables around the world—the lines of fiber that traverse open oceans across the globe.

In these cases, Clark says, there are two regions of each cables’ path. There’s the deep sea portion—the Davy Jones’ Locker realm where only top-secret missions and movie directors on submarine jags dare venture. And then there are the portions of cable in shallower waters, typically nearer to coasts, that are accessible by present day anchors, submersibles, drones, and lord-knows-what-other kinds of underwater tech.

Moreover, once an undersea cable ventures into the legal purview of a given country—what’s called a nation’s exclusive economic zone (EEZ)—that in particular is when fancy, newfangled tech to defend or attack an undersea line must take a backseat to old-fashioned military and policing might.

Satellite imaging and underwater drones, says the Hudson Institute’s Bryan Clark, are two technologies that can protect undersea fiber optic lines. Hudson Institute

“If you were patrolling the area and just monitoring the surface, and you saw a ship [traveling] above where the cables are, you could send out Coast Guard forces, paramilitary forces,” Clark says. “It would be a law enforcement mission, because it’s within the EEZs of different countries who are owners of those cables.”

In fact, the Danish navy reportedly did just that concerning the Baltic voyage of a Chinese-flagged chip called Yi Peng 3. And now Sweden is calling for the Yi Peng 3 to cooperate in an inspection of the ship in a larger investigation of the undersea cable breaches.

One-Million-Plus Kilometers of Open Cable

According to Lane Burdette, research analyst at the internet infrastructure analysis firm TeleGeography, the vastness of undersea internet lines points to a dilemma of shoring up the high-vulnerability shallow regions and setting aside for the time being the deeper realms beyond protection.

“As of 2024, TeleGeography estimates there are 1.5 million kilometers of communications cables in the water,” she says. “With a network this large, it’s not possible to monitor all cables, everywhere, all the time. However, new technologies are emerging that make it easier to monitor activity where damage is most likely and potentially prevent even some accidental disruption.”

At the moment, much of the game is still defensive, Clark says. Efforts to lay undersea internet cable lines today, he says, can also include measures to cover the lines to prevent their detection or dig small trenches to protect the lines from being severed or dragged by ships’ anchors.

Satellite imaging will be increasingly crucial in defending undersea cables, Clark adds. Geospatial analysis offered by the likes of the Herndon, Va.-based BlackSky Technology and SpaceX’s Starshield will be essential for countries looking to protect their high-bandwidth internet access. “You’ll end up with low-latency coverage over most of the mid-latitudes within the next few years, which you could use to monitor for ship operations in the vicinity of known cable runs,” Clark says.

However, once UUVs are ready for widespread use, he adds, the undersea internet cable cat-and-mouse game could change drastically, which UUV being used offensively as well as defensively.

“A lot of these cables, especially in shallow waters, are in pretty well-known locations,” he says. “So in the Baltic, you could see where Russia [might] deploy a relatively large number of uncrewed vehicles—and cut a large number of cables at once.”

All of which could one day render something like the Yi Peng 3 situation—a Chinese-flagged freighter trawling over known runs of undersea internet cabling—a quaint relic of the pre-UUV days.

“Once you’ve determined where you’re pretty sure a cableway is, you could drive your ship over, deploy your uncrewed vehicles, and then they could loiter,” Clark says. “And then you could cut the cable five days later, in which case you wouldn’t be necessarily blamed for it, because your ship traveled over that region a week ago.”