With threats to subsea cables increasing, European countries need to step up to secure their interests.
Editor’s Note: Russian cable-cutting and other types of sabotage pose a threat to Europe’s communications and energy infrastructure. Carnegie’s Sophia Besch and Eric Brown argue that Europe has begun to respond, but slowly, and that the EU and European states should step up their ability to detect sabotage, tighten their laws, and otherwise act decisively to deter and counter such attacks. – Daniel Byman
The web of subsea data and energy cables, already vital for the functioning of global society, will only grow in importance in the coming years. A recent string of “incidents” in the Baltic Sea involving damaged European undersea infrastructure has highlighted just how vulnerable these linkages are. The past two years have been a crash course for European authorities on how to protect their subsea cables and pipelines.
Luckily for Europeans, the recent cable and pipeline cuts in the Baltic Sea have had limited impacts on public life. And, after each incident, European authorities have responded more boldly than before. Yet, much as Europeans have learned from these recent incidents, so too have potential adversaries. Some experts even speculate that the Baltic Sea is being used as a “testing ground” for subsea sabotage techniques.
Europe risks not only continued vulnerability to isolated instances of damage if remaining gaps are left unaddressed but also the inability to respond to concerted acts of aggression. They must apply the lessons learned over recent years to achieve adequate deterrence, repair, and resilience capabilities—the holy trinity of dealing with hybrid attacks against subsea infrastructure.
First, Europeans should lead a global push to update inadequate domestic legal regimes and reinterpret international maritime law to protect against damage to subsea infrastructure. Second, European countries should create new partnerships with industry leaders to expand global cable repair capabilities, upending the current market-driven model. Third, the European Union should leverage its position to help expand trusted subsea networks to countries wary of picking sides in the broader U.S.-China technological competition. This dynamic will become increasingly important as U.S. tech moguls position themselves closer and closer to a Trump administration openly hostile toward Europe and Europeans increasingly lose trust in the firms that provide digital services and their underlying infrastructure.
The stakes are high. In February of this year, Latvia, Lithuania, and Estonia finally disconnected from Russia’s Soviet-era grid and joined the European Continental Network. This move makes the web of underwater cables that supply energy and data to European countries more critical than ever. Demand for Norwegian oil and gas, transported through pipelines to mainland Europe, has also spiked since Russia’s invasion of Ukraine. Beyond Europe, incidents of suspicious cable cuts have increased as well, particularly near Taiwan. In March 2025, the Chinese government disclosed its possession of a deep-sea cable-cutting device—the first time any country has officially done so.
Using the Full Power of the Law
The first step in deterring attacks on subsea infrastructure is to catch the perpetrators. Doing so requires advanced surveillance to identify suspected vessels and the legal authority to stop them from sailing on. In response to the recent cable cuts, both NATO and the U.K.-led Joint Expeditionary Force (JEF) have introduced new initiatives to enhance surveillance of suspicious vessels and increase naval patrolling in the Baltic and North seas. The EU has also released a new “Action Plan on Cable Security,” which emphasizes detection as a key priority. These collaborative efforts are useful; they can assist smaller countries in NATO’s northeast that lack the naval capabilities to monitor and interdict suspicious vessels on their own. European countries are also investing in new technologies, including drones and advanced underwater sensors, to gain a clearer picture of activity under the water’s surface.
Once a suspected vessel has been identified, authorities must make sure they possess the legal authority to stop it. The UN Convention on the Law of the Sea (UNCLOS) reserves criminal jurisdiction for intentional subsea cable damage beyond territorial waters (up to 12 miles off the coast) for a ship’s flag state, not the state(s) connected to the cable. Only Article X of the 1884 Convention for the Protection of Submarine Cables grants officers from warships the ability to board a vessel suspected of intentionally damaging a cable outside of territorial waters (though criminal jurisdiction for punishing actors for the damage still remains with the ship’s flag state). Several European countries—including Estonia, Finland, Latvia, and Lithuania—are not signatories to this 140-year-old document, hindering their ability to act when subsea infrastructure damage occurs in a coastal state’s exclusive economic zone (EEZ) or the high seas.
In the two most recent instances of Baltic Sea cable cuts, Finnish and Swedish authorities were willing to chase down and board vessels believed to have damaged subsea cables. In the future, consistently improving regional intergovernmental and interagency coordination will be crucial to achieve a coherent forceful response. But in both cases, the targeted vessels complied with authorities’ requests to enter Finnish and Swedish territorial waters, where they were then boarded by police. Europeans cannot assume all ships will be so cooperative, especially if engaged in acts of deliberate sabotage. Had the ships stayed outside of territorial waters, like the Chinese-flagged Yi Peng 3—which is suspected of damaging two Baltic Sea cables in November 2024—European authorities would have lacked jurisdiction under their current interpretation of international maritime law to board without explicit permission from the flag state.
Several legal avenues exist that would allow authorities to arrest vessels beyond territorial waters for damage to coastal states’ subsea infrastructure. European governments can, for instance, change their interpretation of international law from refusing to assert extraterritorial criminal jurisdiction under UNCLOS to doing so based on other existing legal principles. To be sure, any such measure will likely lead to restrictions on freedom of navigation in European waters, which could lead to spillover in other operational theaters like the South China Sea.
European states connected to subsea cables and pipelines can also introduce domestic legislation criminalizing damage to their underwater infrastructure outside of territorial waters. Estonia is already working on this, amending its domestic laws to criminalize damage to subsea cables in areas outside its sovereignty. All EU and NATO members that are not signatories of the 1884 Cable Convention should also become so immediately or, like the United States, interpret Article X of the convention as customary international law.
After a ship is caught, the next step is sufficient retribution. Unfortunately, not all European countries have domestic laws and regulations that appropriately punish both accidental and intentional damage to subsea cables in their territorial waters. EU and NATO coastal states should review their penal codes, updating where necessary, to ensure all damage to subsea cables in their territorial waters is severely penalized, including through longer prison sentences for responsible crew, fines, and the possibility to impound responsible vessels. Again, Estonia is a model here, with officials considering markedly increasing prison times and fines for intentional and accidental damage to its subsea cables. The Estonian parliament is even set to vote on legislation that would allow Estonia’s navy to sink civilian vessels that threaten undersea infrastructure and refuse to comply with authorities’ demands.
Finally, European countries should exert more pressure on states to ensure that vessels flying under their flag are not damaging critical European infrastructure. Europeans can, for instance, impose economic costs, such as sanctions or making access to EU maritime infrastructure projects conditional on zero involvement in damaging European subsea infrastructure. They must signal to captains and flag states alike that they are serious.
Fixing a Broken Repair System
The global cable repair fleet for undersea cables is small and aging. It is also nearly exclusively in the hands of the private sector, with profit motive driving many of the ships available to prioritize the more lucrative activity of laying cables during this period of high demand over repair operations. Of the limited number of repair ships that exist, many also are not able to service heavier power cables. While the average repair time for subsea data cables in 2023 was 40 days, repairs to the Estlink 2 power cable between Finland and Estonia—which was severed in December 2024—are expected to be completed in late spring 2025. It took months to even find a suitable ship and crew to conduct the repair.
The current global repair fleet is barely suited to service the 150 to 200 cable breaks that occur yearly by accident or natural hazard—let alone a crisis scenario in which multiple European cables are targeted in a concerted attack. European governments and militaries must be prepared for the worst. The U.S. government, in comparison, has established a “Cable Security Fleet,” comprising two private repair vessels that are available during emergencies to service cables connected to the United States. Washington pays the U.S. cable giant SubCom $10 million annually ($5 million per ship) as part of this agreement, though there are question marks over the future of that funding.
The EU should follow a similar model with one or more of Europe’s cable industry leaders to guarantee at least as many repair vessels are available to service European cables in crisis scenarios. Encouragingly, in its new Cable Action Plan, the EU plans in the “medium term” to both support the acquisition or contracting of additional cable repair ships, as well as establish the EU’s own “Cable Vessels Reserve Fleet.” Ideally, the European and U.S. cable fleets could then form a transatlantic trusted repair system that is less reliant on the current market-driven business model of cable maintenance.
An EU or transatlantic fleet of trusted cable repair vessels would also offer strategic advantages in regions like the Indo-Pacific. Offering better repair capacities would benefit countries in the region, which often enjoy fewer redundancies in their subsea connections than Europe or the United States. And increasing the number of non-Chinese options for cable maintenance and repair should be welcomed by officials in Washington, who for years have been pressuring partners to avoid granting access to Chinese vendors.
Investing in Redundancies
In addition to challenges related to deterrence and repair, the recent cable cuts in the Baltic Sea underscore the need for network resilience through redundancies. For example, the Estlink 2 power cable is only one of two such interconnectors between Finland and Estonia. It is no surprise that the Estonian navy sent a patrol ship to guard Estlink 1, the other power cable to Finland, immediately after Estlink 2 went offline. And in December 2024, Finnish authorities acted quickly to arrest the Cook Islands-flagged Eagle S largely out of a concern that the ship would drag its anchor over the Balticconnector gas pipeline.
European states are investing both individually and jointly to fund new projects that enhance critical underwater resilience and should continue to do so. These include initiatives like NATO’s HEIST project, which aims to reroute connectivity data to satellites in instances of cable faults, and EU-funded cable projects under the digital portion of the Connecting Europe Facility (CEF Digital).
Yet, for the EU especially, more money cannot substitute for a lack of strategic thinking with respect to what projects receive funding and how much. The EU announced more than a year ago that it would identify strategic Cable Projects of European Interest (CPEIs) but so far has yet to do so. Moreover, in the most recent CEF Digital call for proposals, even though applicants are encouraged to demonstrate that their project has geostrategic importance, projects are not evaluated on the merit of this criteria. EU personnel evaluating the proposals should prioritize a select number of strategically important proposals, rather than simply spreading funds across more projects. For example, the EU should prioritize subsea cable construction projects in the Arctic as a rapidly emerging strategic region.
So far, the EU has focused on funding cable projects that connect to Europe or its overseas territories. Policymakers in Brussels should also do more to help European cable installers, like France’s global market leader Alcatel Submarine Networks, secure new deals beyond Europe—especially those that aim to increase redundancies for less-served countries. Subsea critical infrastructure has increasingly become a new arena for U.S. technological and economic competition, with countries being forced to choose between cables supplied and operated by U.S. or Chinese vendors. EU support to help increase network resilience could be a convenient alternative for those feeling stuck between Washington and Beijing.
Implications Beyond the Baltic
The effects of any measures taken by European governments following these incidents in the Baltic Sea—whether on deterrence, repair, or resilience—will have implications around the world. Actions taken against Chinese- or Russian-flagged vessels in the Baltic Sea might have ramifications for European-flagged ships in the South China Sea. Closing EEZ corridors in Baltic Sea straits might prompt other countries to do the same elsewhere, impacting freedom of navigation in those areas. An EU or transatlantic cable repair fleet has the potential to alter the way in which cable maintenance has been conducted to date. And additional redundancies, both in Europe’s immediate neighborhood and elsewhere, can shape power dynamics among countries connected to those cables.
European policymakers must consider these effects but should not let themselves be prevented from acting decisively. Rather, the recent Baltic Sea incidents present Europeans with an opportunity to lead a global push, with partners, to reshape subsea data and power cable protection through improved legal standards, enhanced repair capacities, and expanded trusted networks. If Europe does not act now on its own terms, it risks allowing others to shape this dynamic realm in unfavorable ways.
Because of the global implications of any action taken within Europe or its waters, European countries should proactively coordinate on subsea cable protection and security with international partners like Australia, Japan, and especially Taiwan. The EU should encourage partners to endorse the “New York Statement,” a nonbinding agreement from October 2024 focused on improving cable protection, resilience, and redundancy. In doing so, the EU could also host a follow-up meeting for signatories to discuss lessons drawn from their respective regions. NATO, which has assembled a group of lawyers to work on the legal elements of subsea infrastructure protection, should lead exchanges with its partners in the Indo-Pacific engaged in similar efforts. The recent decision by Taiwanese prosecutors to charge a Chinese ship captain with intentionally damaging subsea cables makes the need for such exchanges even more timely.
Conclusion
As calls grow even louder from Washington for Europe to take responsibility for its security and defense, subsea infrastructure protection is one area in which Europeans can take the lead now—in Europe, and globally, with international partners. The increasing dominance of U.S. tech firms and their close relationship with a coercive Trump administration should hasten this process.
– Sophia Besch, Erik Brown, Published courtesy of Lawfare.
