Seabed Warfare

Countless submarine cables are the communicative backbone of a globalized world of states. Today they form a “new front line”. The same can be said of other elements of critical offshore infrastructure like wind turbines and pipelines. However, the legal regime for the protection of submarine cables is hopelessly outdated. While treaty provisions for the protection of critical infrastructure under the law of the sea are weak, a change of this treaty regime is unlikely. A change of state practice within this framework seems to be the only viable way to improve the level of protection.

Legal Regulations for the Protection of Submarine Cables

The United Nations Convention on Law of the Sea (UNCLOS) of 1982 is a product of its time: Manganese nodules were considered a future-oriented source of raw materials (Part XI, Section 2), but it was far beyond the imagination of the drafters how much the internet is now an essential staple of societies and working environments. UNLCOS Art. 113 addresses the Breaking or injury of a submarine cable or pipeline. This merely obligates states to criminalize such acts but does not grant authority for enforcement measures against foreign ships.

Inside territorial waters of the 12-mile zone coastal states may undertake monitoring measures pursuant to their sovereignty on the basis that such activities render a passage non-innocent. It is difficult to argue in favor of a right of inspection for coastal states against vessels outside territorial waters within the Exclusive Economic Zone (EEZ) of up to 200 miles. UNLOS grants “sovereign rights for the purpose of exploring and exploiting, conserving and managing the natural resources”  (Art. 56 (1)(a)) like building wind farms but does not confer powers of law enforcement. States are authorized to protect the marine environment (Art. 56 (1) (b) (iii)). Coastal States may use their right of hot pursuit against a ship that has caused an oil spillage or gas leakage (Arts.79 (II), 221 in combination with Art. 111(2)), but a similar right does not exist in relation to submarine cables.

The International Law Association (ILA), established in 2018 a committee to examine the current international legal regime governing submarine cables and pipelines. Its third report focused on the measures that states can take in response to intentional acts of damage to submarine cables and pipelines committed by States and non-State actors in peacetime. As the ILA stated in this report: “There is nothing in the LOSC which expressly permits warships of States other than the flag State to interdict vessels suspected of breaking or injury of submarine cables or pipelines in the high seas.” (ILA, Submarine Cables and Pipelines under International Law, 3. Interim Report 2004 p. 16, No. 46.).

This makes the 140 years old Article 10 of the 1884 Paris Convention for the Protection of Submarine Telegraph Cables crucial for the current protection regime of submarine cables. Though this article is considered by some states to reflect customary international law (ILA, 2024 Report, p. 16), there is hardly any state practice regarding its implementation.  It is ultimately for a competent court to decide on the status as a rule of customary international law. Yet, this misses the point: A mere boarding and questioning of the crew before continuing its journey will not suffice to deter a vessel or state from engaging in this kind of activity.

Recent Developments in the Baltic Sea

Numerous incidents over the last months have made it difficult to keep track: On December 29, 2024, the Eagle S, a crude Oil Tanker sailing under the flag of the Cook Islands, allegedly cut two fiber-optic cables between Estonia and Finland. The vessel was seized by Finish authorities and moved to an anchorage in Porvoo, 25 miles east of Helsinki.

Just before Christmas, on December 19, 2024, Swedish, Danish, Finnish and German authorities managed to board and inspect the Yi Peng 3, a Chinese-flagged bulk carrier with a Russian captain. The ship was moored in the Kattegat off the Danish coast outside territorial waters. The legal basis for boarding the vessel was an invitation by the flag state to observe an investigation by Chinese authorities. The Swedish Public Prosecutor leading the criminal investigation into the destroyed cables was denied from boarding. After this inspection the vessel continued its voyage.

This was the result of a previous four and a half weeklong stand-off: On November 17, 2024, the Yi Peng 3 dropped anchor off Sweden and continued sailing with its anchor dragging on the ground. A submarine telecommunications cable connecting Sweden and Lithuania (BCS East-West Interlink) was cut. The next day, the C-Lion 1 submarine telecommunications cable, linking Finland and Germany was cut. Both cuts (also referred to as C-Lion1 incident) occurred within the exclusive economic zone (EEZ) of Sweden. The Yi Peng 3 sailed on toward the Danish Straits and stopped just outside Danish territorial waters.

Given prior political developments this seems to be no coincidence: On the day of the first cable-cut, November 17, 2024, the United States had  lifted the restrictions on Ukraine’s use of long-range Army Tactical Missile Systems (ATACMS) to attack Russian territory.  Since an anchor winch represents the crudest form of mechanical engineering, it seems virtually impossible for incidents like these to happen accidentally. They highlight that the legal regime for the protection of submarine cables is under pressure. This partly has historical reasons, but is also an indicator of traditional  “sea blindness” in western states.

Grey Zone Aggression and Extension of “Seabed Warfare” to the Baltic Sea

The current developments in the Baltic Sea must be placed in a greater context of so-called Grey Zone aggression. A Grey Zone conflict is not a legal term but a metaphor to describe a state between armed conflict and peace. Grey Zone operations encompass coercive actions falling below the threshold of armed conflict but surpassing normal diplomatic and economic measures.  Such an approach is becoming an increasingly common method of Chinese and Russian foreign policy and the seabed with its highly vulnerable infrastructure is a prime field of activities. In September 2024, US and British intelligence services specifically warned of a Russian campaign of sabotage activities against submarine cables. Russia is continuously developing underwater warfare capabilities, as Flotilla Admiral Christian Meyer, stated in a hearing in the German Bundestag in June 2024.

Selected security related incidents show that a dedicated situational awareness is needed in and on the Baltic Sea. The best-known events of this kind include unknown submarine sightings off Sweden, the sabotage of the Nord Stream gas pipelines, the systematic appearance of Russian research vessels near critical maritime infrastructure, the increasing traffic of a “shadow fleet” in the Baltic Sea and regular naval maneuvers the Russian Navy, sometimes with the participation of forces from China or India. As a result, German Bundeswehr naval command stationed in Rostock with the Commander Task Force Baltic (CTF Baltic) now provides additional tasks for NATO.

Conclusion

The latest developments may help to overcome a negligence of matters of maritime security, or simply “sea-blindness”. Submarine cables are attractive targets for acts of sabotage. To be less vulnerable, more effective deterrence and more resilience are required. As a major adjustment of the UNCLOS seems downright impossible, this matter must be addressed within the existing legal framework. Likewise, commendable calls for a specific convention seem pointless. Actually, a whole catalogue of measures can be taken without altering the current legal regime:

Necessary are robust enforcement measures that states may take in response to either threats or actual acts of damage to submarine cables. These enforcement measures must go beyond boarding, inspection and search of a ship suspected of prohibited conduct. They must include any combination of arresting the vessel or arresting persons aboard as interdiction of vessels. A ban issued by the EU against currently 79 (non-EU) vessels from Russia’s shadow fleet subjecting them to a port access ban and a ban on provision of services effectively increases the costs for such actions.

Furthermore, states should amend their domestic legislation and make it a specific criminal offence to intentionally destroy or damage international submarine cables. The Annex VII-Arbitral Tribunal stated in 2015 in the Arctic Sunrise case that it might be lawful for coastal States to take additional preventive enforcement measures in the EEZ against a suspected terrorist attack (para. 278) and indicated that states may resort to enforcement measures beyond UNCLOS based on general international law (para. 235). Hence coastal States may consider taking enforcement measures against suspected ships based on the customary law of necessity (Art. 25,  Draft Articles on State Responsibility).

There are serious security gaps in the current legal regime for the protection of  submarine cables and affected states are still struggling for answers. As states challenging the status quo undertake more aggressive actions, this requires far more consequent enforcement measures on part of challenged states in order to uphold international law.