Hybrid warfare on the seabed?

It's an inconspicuous cable, thinner than a firehose, but equipped with eight high-performance fiber-optic pairs coated in steel and a waterproof protective layer.

The underwater communication cable Cinia C-Lion 1 connects the Finnish capital, Helsinki, with the German port city of Rostock, about 1,200 kilometers away. It serves as a sort of data highway, connecting data centers in northern and central Europe.

When it was laid across the Baltic Sea, an underwater plow was used to carve a meter-deep trench in the seabed to ensure that the cable would be very well protected. And yet, despite this, it was broken near Oland, an island just off the coast of Sweden, in the night of Sunday into Monday. Shortly before, another data cable running between Sweden and Lithuania sustained similar damage off the coast of Gotland, another Swedish Island.

The crew of a Chinese freighter, along with its Russian captain, are now suspected of sabotage. The cargo ship is believed to have passed both sites when the damage occurred. Citing public maritime data, the Swedish television channel SVT reported that the ship sailed from a Russian port. It was also said to have temporarily switched off the transponder required to determine its position.

According to the website marinetraffic.com, the ship is currently anchored in open water between the coasts of Sweden and Denmark. The Danish authorities report that their navy is closely monitoring the vessel.

A Danish naval vessel keeps the Chinese freighter Yi Peng 3 under surveillance in the Kattegat straitImage: Mikkel Berg Pedersen/Ritzau Scanpix Foto/AP/dpa/picture alliance

Not the first incident in the Baltic Sea

Moritz Brake, an expert in maritime security at the Center for Advanced Security, Strategic, and Integration Studies (CASSIS) at the University of Bonn, says these events closely resemble an incident on October 7, 2023, which also occurred in the Baltic Sea.

Here too was a Chinese cargo ship involved. A container freighter sailing between Sweden, Finland, and Estonia under a Hong Kong flag damaged two data cables and the "Baltic Connector" gas pipeline with a trailing anchor — supposedly by accident.

Brake does not believe this was unintentional. "The anchor was dragged across the seabed for about 180 kilometers. That can't possibly be an accident, where nobody notices that it's happening."

Furthermore, the freighter was accompanied by supposed Russian research vessels, and the incident occurred on the birthday of Russian President Vladimir Putin.

"Those are just too many coincidences coming together all at once," says Brake.

Western intelligence agencies have long been concerned about supposed Russian research ships cruising the seas of northern Europe and potentially spying on Western infrastructure.

As far as the recently damaged data cables are concerned, they may not have needed to. The locations of undersea cables worldwide can easily be found in open-source data online.

In the case of the severed C-Lion 1 cable in the Baltic Sea, the Finnish operator Cinia had previously explained in a promotional video (now archived) that a large part of the cable was laid in 2015 parallel to the Nord Stream pipeline, which supplied Europe with Russian gas. This allowed Cinia to "rely on existing seabed surveys, enabling the project to be realized just one year after planning was initiated."

The Nord Stream pipeline was itself targeted with explosives in September 2022. It has still not been established who was behind that attack.

Gas leaking from the Nord Stream pipeline, which was targeted with explosives in September 2022Image: Danish Defense Ministry/Xinhua/picture alliance

Limited damage but a powerful signal

The actual damage from this latest act of sabotage is limited.

"It happens 100 to 150 times around the world that cables are accidentally damaged," Brake told DW. "That's why infrastructure is designed so that other cables can offset the damage. It's really not a problem; generally, users don't even notice."

However, Brake emphasizes that this is critical infrastructure. More than 90% of global data traffic flows through undersea cables.

"If you deliberately target key nodes, if you demonstrate, as here, that two cables can be damaged within a short space of time, then it's possible that next time, even more cables could be damaged. And then we'll quickly encounter serious problems."

These acts of sabotage also affect our market economies, he says. Investors might be deterred from putting money into maritime infrastructure if protection cannot be guaranteed.

 "In Sweden, the government had to cancel several offshore wind projects because of defense concerns," Brake explains.

Sweden, a global leader in wind power, was forced to cancel projects in the Baltic Sear over defense concernsImage: Dalibor Brlek/picture alliance

These actions also indicates something that should not be underestimated: There is a developing and "increasingly close collaboration between not just China and Russia, but also Iran and North Korea," Brake says. 

"They've been working together for a long time now to act against Western interests worldwide, sometimes with extreme measures, and now we see it in cases like these."

He believes that the West is being tested by these acts of sabotage. "The question is: How will we react to such an incident? Detaining the ship, NATO channels, information sharing — this is definitely the other side testing our response strategies."

Impossible to provide 100% protection

But how can we better protect ourselves against these acts of sabotage? Oceans cover three-quarters of the Earth's surface, and more than 500 data cables now lie in their waters, a total length that would go around the Earth 30 times. Data networks, maritime trade, oil and gas pipelines — all are affected, and, as Moritz Brake says, it's impossible to monitor and secure all of them comprehensively and all of the time: "The enemy only needs to succeed in one place, while we must constantly protect the entire global system."

Analyst Moritz Brake believes NATO will need to expand its naval surveillance capabilities to counter-sabotageImage: Ramon van Flymen/ANP/IMAGO

So Western societies will have to find ways of dealing with acts of sabotage — but Brake says they are not powerless against them. "We can at least strengthen our monitoring capabilities so that we will be able to detect, document, prove, and reveal when other actors are wreaking havoc on our infrastructure."

This, he says, could be a way of deterring them. "We can show them: If you threaten us somewhere here, we can take countermeasures. Not in the same place, maybe, but somewhere else."

To Brake, the meaning of the latest incident is clear: "There are aggressors at sea who hope to remain unidentified. And we have to do something about that."

This article has been translated from German.