Submarine cables, responsible for carrying over 99% of global internet traffic, are a vital part of Europe’s critical undersea infrastructure, which also includes gas pipelines and power cables placed along or buried under the seafloor. Recent disruptions by merchant vessels in the Baltic Sea, such as the Newnew Polar Bear in October 2023, the Yi Peng in November 2024 and the Eagle S in December 2024, demonstrate a growing trend to intentionally damage undersea infrastructure using ship anchors. 

The normalisation of this grey-zone tactic has raised security concerns amongst European and NATO states, as approximately 3,000 vessels, or 3% of the world’s total, transit through the Baltic Sea on any given day. The increased military presence and heightened suspicion of sabotage by any vessel in the area creates a tense operating environment. After two submarine cables were cut in January 2025, Norwegian authorities detained a Russian-crewed vessel, while Swedish authorities detained a Bulgarian vessel. While both were suspected of involvement, they were subsequently cleared. In May 2025, as NATO forces sought to detain a sanctioned ship suspected of attempting to cut cables, a Russian jet was deployed to ensure its safe passage. 

More than 50 submarine cables connect countries surrounding the Baltic Sea, and while network redundancies ensure operations continue with minimal impact when a single cable fails, simultaneous or sequenced cable disruptions can oversaturate networks and cut off entire regions in Europe, a problem compounded by limitations in repair capabilities. 

Resources for repairs are scarce. The fleet equipped for the task is limited, with current estimates at more than 80 cable-laying and repair vessels in operation worldwide. Due to the frequency of cable failures and an increase in global connectivity projects, these ships are in high demand. In some regions, like Southeast Asia, restrictive policies have delayed the repair process due to administrative processes and cabotage policies, which require permission to enter certain waters and the involvement of local vessels. The 40% of cable vessels owned by firms headquartered in Europe are frequently contracted to maintain existing cable systems through marine maintenance agreements driven by the private sector and designed to defray costs.

In terms of the global manufacture and installation of cables, 98% are handled by four private firms: the US company SubCom, French firm Alcatel Submarine Networks, Japanese firm Nippon Electric Company and Chinese firm HMN Technologies. Should states seek to build resilience to cable disruptions, such as by stockpiling, this concentration creates supply risks. There is therefore potential for greater diversification of the global manufacture and installation of cables, which will need to be a public-private endeavour.

Efforts in Europe are under way to strengthen the resilience and redundancy of critical undersea infrastructure. In February 2025, as part of its EU Action Plan on Cable Security, the European Commission (EC) said it intends to redirect almost EUR1bn into digital infrastructure, including submarine cables and surveillance capabilities, amid concerns over recent Baltic Sea disruptions. The EC, together with member states and industry partners, will support the development of new surveillance tools and mechanisms to monitor the vast stretches of submarine cables and improve threat response. Commercial sensors that can be placed along submarine cables or on the seabed – along with uninhabited air and subsea vehicles – can detect changes in vibration and temperature to monitor for physical cable damage, warn of potential acts of sabotage and deliver alerts in the event of an outage.

In January 2025, NATO launched the Baltic Sentry exercise to protect critical infrastructure in the Baltic Sea with the deployments of a range of assets, including frigates, maritime patrol aircraft and uninhabited maritime vehicles. The Alliance will also integrate national surveillance assets through the Critical Undersea Infrastructure Network composed of government representatives and industry experts, such as from the technology and energy sectors. The network was established in February 2024 to explore new ways to protect infrastructure and improve resilience of underwater assets. As of 2023, the European Union has also launched a Critical Seabed Infrastructure Protection project, which would improve its ability to defend undersea infrastructure using uncrewed undersea vehicles.

In the medium term, the EC seeks to secure a stockpile of spare parts and to build or contract its own reserve cable-repair fleet. This will require public-private partnership, as new cable ships cost around US$100m to build. Separately, the Italian multinational company Prysmian signed a seven-year framework agreement with Dutch subsea services specialist N-Sea in March 2025 to provide a dedicated vessel for rapid response to disruptions in Europe. Further consultation with industry might allow the EU to better support private-sector driven cable maintenance and repair agreements in the Baltic Sea, like those in the Atlantic Ocean and Mediterranean Sea. In the long term, a European push to build cable vessels could indirectly support resilience efforts in other regions, like the Indo-Pacific, and vice versa. For example, the Singapore-based company Megamas Resources signed a letter of intent with the German Lloyd Werft Bremerhaven shipbuilder to construct a new cable-laying vessel, citing the global shortage of such vessels.