A Key Aspect of Subsea Warfare: Cable Cutting

On Christmas Day, one of two cables connecting Finland’s electricity grid to Estonia, Latvia and Lithuania was cut. Four data cables—three linking Finland and Estonia and one between Finland and Germany—were broken at the same time.

This and two earlier instances have heightened concerns about the vulnerability of Europe’s undersea infrastructure, prompting calls for enhanced security measures and international cooperation to safeguard critical communication and energy links.

It’s also a timely reminder to Indo-Pacific countries to think about how their region is similarly vulnerable to subsea sabotage.

Once could be an accident, and twice might be a coincidence. But three instances look like a trend that we shouldn’t ignore or tolerate, especially since we know malign actors like Beijing and Moscow also have the capability to disrupt our critical infrastructure through prepositioned malware.

Finnish authorities are investigating the outage. On 26 December, Finland used heavily armed elite units to board and forcibly detain a tanker, registered in the Cook Islands but in fact Russian, suspecting its crew had deliberately severed the cables. Finnish authorities say the tanker, which was carrying oil, is part of Russia’s effort to avoid international trade sanctions. The ship is also reported to have been equipped for listening to radio transmissions as an intelligence gatherer.

Finnish authorities could board the ship and arrest its crew without the consent of its owner or the country of registration only because it was in Finnish waters. But doing so still required Finland to have the political will to take bold action.

Several data cables and a pipeline connecting Finland and other Nordic countries to the European mainland have been severed in the past year in suspected deliberate anchor-dragging incidents. Jukka Savolainen, a Finnish navy officer and director of the European Center of Excellence for Countering Hybrid Threats, a body established by NATO and the European Union, has suggested publicly the high number of similar cable breaks shows that the perpetrators are testing whether cheap civilian ships can cause disruptions of critical infrastructure.

The latest Finnish incident follows the simultaneous severing of two undersea data cables in mid-November. The BCS East-West Interlink cable, connecting Gotland to Lithuania, was severed around 17 November, causing substantial disruptions to telecommunications services.

The next day, the C-Lion 1 submarine telecommunications cable, linking Helsinki to Rostock, Germany, was also cut. The damage was detected near the southern tip of Sweden’s Oland Island. The operator, Cinia Oy, said an external force had severed the cable.

Both cables were restored by 28 November. Investigations are ongoing, involving authorities from Sweden, Finland, Lithuania and Germany. A China-flagged ship, Yi Peng 3, which was present near the disruption sites, has been a focus.

On 23 December Swedish authorities said China had denied a request for prosecutors to conduct an investigation on the ship. It left the area soon after. If, as seems very probable, the crew were saboteurs, investigators cannot now hold them accountable. Swedish authorities have criticised China for withholding full access to the vessel.

According to the United Nations Convention on the Law of the Sea, China, as the home state of the vessel, is not obliged to give other countries access to it. And only China holds the sole authority to prosecute. The ship was detained in international waters, so Swedish police could only observe the situation; they could not investigate. An accident commission could separately interview the crew and examine the anchor but could not prosecute. Legally, Sweden has limited options beyond seeking economic compensation from the ship’s owner.

Since China has persistently breached the same convention in the South China Sea, its disregard for the interests of other countries in the Yi Peng 3 case comes as no surprise.

The key point is the rest of the world, which does care about such rules, can’t afford to let malign actors continue to get away with it.

Beijing’s refusal to cooperate fully with investigations erodes trust and transparency. These are particularly crucial in incidents involving shared resources, such as undersea cables, which serve as critical infrastructure for multiple nations. A refusal to comply with international investigative norms also encourages other states to act similarly.

China is also ignoring its responsibility to assist in uncovering the truth and ensuring accountability, undermining cooperative norms that underpin a global rules-based order. Under international law, states must prevent and address harm caused by their vessels in foreign or international waters.

Furthermore, disruption of undersea cables not only affects regional communications; it also has significant economic implications and poses risks to broader economic stability. So, China’s non-cooperation exacerbates tensions in Europe and raises concerns about its commitment to preserving the stability of global infrastructure.

Good international citizenship requires states to act in a manner that supports global security. They should be transparent and accountable. China’s refusal to cooperate fully and Russia’s continued effort to break sanctions are at odds with these principles. These incidents show how the Russia-China axis is increasingly working in sync to the peril of the rules-based liberal order. Political will, and unity of purpose, is needed to make clear this is intolerable.

Jakub Janda is director of the European Values Centre for Security Policy, and James Corera is director of ASPI’s Cyber, Technology and Security Program.

Published on 30 December 2024 by ASPI.