The submarine backbone of the Internet is slipping into the danger zone

Undersea Warfare by Elizabeth Brau about the growing risks to submarine infrastructure.

A fiber optic cable is pulled ashore from the cable-laying vessel Pligel at the entrance to Sassnitz harbor on Rügen Island, Germany in November 2023.

Despite the expansion of Starlink and other communications satellite services, most of the world's Internet traffic still travels through undersea cables that cross the ocean floor. These fiber optic cables co-exist with a network of oil and gas pipelines and undersea power cables – and all these vital links connecting countries and continents are now facing the ever-expanding gray zone wars and open conflicts with growing risks of sabotage.

Growing risks to the world's invisible infrastructure beneath the waves is the subject of a new book by Elizabeth Brau, a senior member of the Atlantic Council who leads the Threats to Global Maritime Order initiative. His book, Submarine Warfare, examines the modern rise of suspicious incidents in which ships that drag their anchors for unusually long periods cut or damage submarine cables and pipelines from the Baltic Sea to the Pacific Ocean.

Brough acknowledges that about 60 percent of submarine cable damage is mainly due to human error during fishing and shipping activities, when heavy nets or anchors are pulled from the seabed. Natural hazards such as hurricanes and undersea landslides also cause fewer such incidents, with a total of 150 to 200 cables damaged each year and usually repaired quickly.

But international tension between superpowers and open warfare in Europe and the Middle East has led to increased scrutiny of cable-cutting incidents, with governments investigating and prosecuting crews for intentionally damaging submarine cables. One of the infamous incidents documented in the book is the "Christmas Day Massacre" of 2024, when a Russian-linked oil tanker, the Eagle S, dragged its anchor from the seabed for about 56 miles (90 km), severing or damaging four data cables and Estlink 2, which connected the submarine's electricity and submarine power cables.

One such data cable was also previously cut by the Chinese cargo ship Yi Peng 3 just a month earlier in November 2024, when the ship damaged two data cables in the Baltic region. The ship's crew has not been prosecuted by European authorities, while the Finnish government has tried to prosecute the Eagle S's three senior officers.

On the other side of the world, the captain of the Chinese ship Hong Tai was convicted by a court in Taiwan of cutting an undersea telecommunications cable in February 2025 and sentenced to three years in prison in June 2025. The legislature of the island's democracy later amended its laws to increase the penalties for willful damage or damage to pipelines.

This year has seen several notable incidents involving overt and covert threats to submarine infrastructure, including Iran's efforts to impose fees on operators of submarine cables that pass through the disputed Strait of Hormuz. Separately, a joint operation involving Britain, Norway and the United States encountered Russian submarines practicing using new technology to disable undersea cables in Arctic waters near Norway's Svalbard archipelago.

What happens when the submarine backbone of the Internet, not critical energy infrastructure, is no longer protected by an almost universal international agreement? Ares spoke to Brow to find out more. (The interview has been condensed and edited for clarity.)

Ars Technica: There's a lot of doubt and tension about undersea infrastructure right now. But it seems that for decades, even during the Cold War, there was a broad international framework that worked mostly where countries generally agreed not to clash too much.

Forehead: Exactly. It worked for a long time, and that's why it's so scary to see that system that really depends on doing the right thing and being a good citizen of the seabed, might not work for much longer.

Ars Technica: I know it's not really any single factor, but I'm curious what factors you'd highlight as major contributing factors to why we're seeing a failure of that general agreement.

Braw: If you think absolutely about the critical nature of submarine cables and pipelines, especially submarine cables…if they were to be disrupted even for one minute, it would be a huge disruption not only in the New York City area, but New York as a financial center. This not only causes operational losses, but also the loss of all the money that goes through the cables every second.

So if you think about the sheer importance of submarine cables to modern societies and modern economies, it makes them an incredibly attractive target. While we had telephone cables during the Cold War, there weren't many of them and we didn't use them. Yes, they were used for international phone calls and telegraphic messages could also be sent. But no one sent telegrams 24/7 and no one made international phone calls 24/7. So they were there, but less important.

Also, despite the cold war and decades of being very dangerous, there was a kind of agreement that when you sign a treaty, you keep it. In fact, the United Nations Convention on the Law of the Sea was adopted in 1982 at the height of the Cold War. So there was an obligation to create some sort of road rules.

Today, that commitment is, I don't want to say it's disappearing, but it's declining among key countries in the world. And at the same time, we see that Russia has discovered that it's really quite useful to use civilian means to weaken other countries, and that's what Russia has specialized in, and other countries may still be specializing in. This makes cables around the seabed a very attractive target.

Ars Technica: Even recently there were reports of how NATO countries apparently thwarted a Russian attempt to sabotage an undersea cable, although that incident happened in the spring.

Braw: The interesting thing about undersea cables and pipelines, especially undersea cables, is not just that we're totally dependent on them. They are not only located within the territorial waters of countries. They connect countries, so they are in international waters [where] countries have no jurisdiction. The oceans are a global commons and the cables live there, and that's why it's so important for countries and everyone who uses the oceans to take care of their surroundings so they don't get damaged.

Then what we've seen in the last few years is that all of a sudden merchant ships in the Baltic Sea and off the coast of Norway and in the waters off Taiwan are getting very sloppy and pulling anchors for long periods of time, which is not supposed to happen as a mariner. You need to know if your anchor is dragging on the seabed, and you know where the cables are.

So it's not supposed to happen, and yet it happened not just once, not just twice, but several times, and it obviously caused considerable anxiety in the affected countries. It also brought considerable costs to the operators as they had to repair the cables, and in the case of power cables, repairing them is very expensive and time-consuming.

We don't know what caused these merchant ships to drag their anchors out of the territorial sea and damage the cables, and we may never know because it's not like those crews are telling us what happened. We only know that these events were very suspicious.

But then we have what you brought up, that Russia and other countries might develop tools to damage other countries' submarine cables using submarines or unmanned instruments or drones attached to submarines, and here we are today. It could still happen, which is why it's always a concern when Russian research vessels prowl around undersea cables. What are they doing there? What is it they are looking at? What do they measure?

China does the same. It sends research ships that wander for long periods in the waters of other countries. And you have to inform the country in whose waters you're doing research that you're doing research and what the nature of your research is, but China doesn't do that. So what do these research ships do? What are they researching?

All this is in the context of increasing geopolitical tension and, by the way, the rapid expansion of the submarine fleet: Western, Russian and Chinese. One, but also the expansion of other submarine equipment, tools, drones, etc.

Ars Technica: Another thing that your book touched on was everything that's been happening around the Strait of Hormuz, and how we've seen Iran threaten or threaten to attack companies that want to run submarine cables through there. At the same time, a number of companies appear to have reconsidered submarine cable projects that were supposed to run through the area.

Braw: This is another fascinating aspect of the undersea cable situation. Therefore, in the Persian Gulf, in the Strait of Hormuz, there are submarine cables, which are necessary not only for the countries connected to it, but also for other neighboring countries. For example, one-third of India's Internet traffic or digital connectivity to the West goes through the Persian Gulf. So this just shows how important these cables are, and not just for the countries that are immediately connected.

In February of this year, the situation was such that three cable projects were about to be launched or were underway. Then the war started and you can imagine that when missiles are flying, drones are flying, it is impossible to install cables on the seabed. Because if you think about ships, it's dangerous enough, but ships are moving. Installation ships are fixed. You really are a sitting duck, so those projects should have been put on hold or abandoned and the companies declared power. Major

But we need submarine cables. So what happens when the world becomes more contentious, more conflicted, or more conflicted? How are cable installation crews and cable repair crews going to do their jobs with various missiles and other weapons flying around them or next to them in the ocean? This is where geopolitics really gets involved with modern economies, and at the forefront are cable installation crews and repair crews.

And then you asked about the tariffs that Iran said it was going to impose. This was a new and, I must say, unsurprising twist on the Iran war. So everyone has heard about the fact that a few weeks after the war, Iran said it would charge tolls on shipping in the Strait of Hormuz, in violation of UNCLOS, the United Nations Convention on the Law of the Sea. Iran said it would do it anyway, and Iran can claim it doesn't need to support the JCPOA, which it has signed but not ratified. But by February, it had upheld UNCLOS and shipping in the Strait of Hormuz was operating well.

Then in March, Iran could say it was no longer committed to the JCPOA because the United States and Israel had violated the UN Charter by attacking it. So why should it support UNCLOS? And that's a dangerous situation we're in, where countries can say, "Well, why should I stick to my treaty obligations when so-and-so doesn't?"

So what Iran said a few months after the war - after that it imposed tolls for shipping for a while - was that it was going to charge tolls from undersea cables in the Strait of Hormuz. And yes, this is a violation of UNCLOS. But he can say, "Well, the United States has violated the UN Charter, so we can do whatever we like."

If you think about the implications, it's not just implications for cable operators in the Strait of Hormuz. How do they pay Iran? How does it work? And what happens if they don't pay? But this is a question for other cable owners. If other countries say, "Well, there are cables in our waters, so we're going to get tolls, because countries don't adhere to UNCLOS anyway, so we might as well."

It's not just that you know the world was in sync, and suddenly there were suspicious cable incidents. It's that law and order in the ocean - and even on land - is deteriorating, and in the midst of all this we're experiencing suspicious cable incidents.

Ars Technica: These submarine cables are obviously of great national interest to governments and may even require military protection in some cases. But at the same time they are being developed by private operators, including many tech giants. We've just seen Meta announce that it's going to lay the first petabit capacity cable across the Atlantic Ocean, and that's part of a much broader undersea cable build. What does this private ownership but conflict of public interest mean for whom, especially with increasing threats?

Brow: This is a very important question. Ever since the first cables were laid on the seabed, they have been privately owned. The cables that were then connected to them were also privately owned. Then in the 1900s, postal services in various countries took over the work of cables. Many cables were government.

Then later in the 1900s, we saw more private cables again. And today, almost all cable is privately owned, typically by consortia. But shorter cables are often owned by the same company. And an important development is what you mentioned as well, is that hyperscalers build their own cables for their own traffic. So, these are private operators, but [cables] are critical national infrastructure. And what governments want may be different. It is actually different from what the operators want.

So people often ask me, "Shouldn't operators install more cables to make sure they always have cables that are operational?" And yes, it can be said that it should, but every cable is a cost in the installation and operation of the cable. Companies look at the hard facts and figures and probably in many cases conclude that the risk of their cables being damaged in destructive ways is less than the cost of adding more cables, and that's a business calculation, right? Whereas for national governments, it would clearly be to their advantage and they would like to see more redundancy. But they don't own the cables and commercial operators are there to make money.

The only other alternative is for governments to subsidize new cables. And I also write about this in the book, what happened to the Matsu Islands [administered by Taiwan]. But we don't have that kind of money to back up every cable on the seabed. Therefore, this conflict is, so to speak, the interests of the owners of Kabul and the interests of the national governments.