Increasing Submarine Cable Sabotage as a Grey Zone Strategy
 
In recent years, sabotage targeting undersea cables have occurred in multiple regions around the world, including the Baltic Sea, Taiwan Strait, and the Red Sea. However, under the current international legal framework remains insufficient to regulate such sabotage or to ensure the effective protection of submarine cable infrastructure. Undersea cables located within a coastal State’s territorial sea or archipelagic waters enjoy a certain degree of legal protection derived from the State’s sovereignty and jurisdiction. By contrast, cables laid in areas beyond national jurisdiction—particularly on the high seas—remain far more vulnerable due to the absence of comprehensive enforcement mechanisms.

Submarine cable sabotage is increasingly being employed as a form of grey zone strategy—deliberately operating in the legal and strategic space between wartime and peacetime. These operations are often difficult to attribute, strategically calibrated to avoid triggering lawful self-defense or constituting an unequivocal use of force under the UN Charter. As the physical layer of cyberspace, submarine cables are an attractive target in strategic competition, as their disruption can generate transnational effects without overt hostilities. International legal bodies such as the International Law Association (ILA) have begun to examine whether such acts may qualify as prohibited uses of force, armed attacks, or threats thereof under customary international law and the UN Convention on the Law of the Sea (UNCLOS). However, existing legal instruments—including the Tallinn Manual—remain limited in practical application, particularly when attribution is uncertain and the conduct falls short of conventional thresholds for state responsibility.

 
Insufficient Legal Protection of Submarine Cables under the Existing International Legal Framework
 
Currently, legal protection against the intentional or negligent destruction of submarine cables is primarily based on three international instruments: the 1884 Convention for the Protection of Submarine Telegraph Cables, the 1958 Geneva Convention on the High Seas, and the 1982 United Nations Convention on the Law of the Sea (UNCLOS). These instruments provide only limited remedies and apply predominantly in post-incident contexts.

Moreover, enforcement options under UNCLOS—such as the right of hot pursuit (Article 111) or the right of visit (Article 110)—are highly constrained in their applicability and do not adequately address the challenges posed by covert sabotage in peacetime.

Under the existing international law, it is inherently difficult to identify and apprehend those responsible, particularly when vessels operate under flags of convenience or conceal their ownership and activities. Even when suspects are interdicted, establishing that they willfully or with culpable negligence caused damage to submarine cables remains a significant legal hurdle. As a result, it is structurally difficult to hold perpetrators accountable, which increases the incentive for actors seeking to exploit this vulnerability.

 
International Response and South Korea’s Strategy
 
In response, countries are building multilateral cooperation frameworks, such as NATO’s recent patrol and monitoring efforts in the Baltic Sea. These include real-time data sharing, joint surveillance, and coordinated patrols. Governments are also partnering with the private sector to enhance recovery capabilities and install sensors on key cable routes. The EU has introduced a strategy to improve resilience and threat detection. Cable protection zones, like those in Australia and New Zealand, have proven effective. There is growing consensus on the need for a new international treaty, and South Korea is participating in joint statements with the United States, the United Kingdom, and Japan to promote cable security, resilience, and shared standards.
 
(1) Korea’s Submarine Cable Deployment Status
 
As of May 2025, Korea has nine international submarine cables, with two more under construction. Most routes are shared, and all but the direct Japan routes are connected via Taiwan. Although a direct cable sabotage by China or Russia is unlikely at present, Korea’s reliance on Taiwan-linked routes could expose it to collateral damage in a Taiwan-centered conflict.
 
(2) Enhancing Public-Private Coordination for Preventive Action and Joint Response
 
While direct attacks on South Korean cables remain unlikely, their global interconnectivity leaves Korea exposed to regional disruptions. To address these vulnerabilities, South Korea should strengthen international cooperation, enhance public-private preparedness, establish domestic cable protection zones, pursue legal reform and contribute to the development of international legal norms. Existing international law system lacks swift enforcement tools.
 
(3) Domestic Preparedness and Legislation
 
Relevant ministries have been working to enhance preparedness against sabotage or attacks. The Ministry of Science and ICT has been conducting legal and technical research, but no concrete national policy has yet been announced. In December 2024, Korea’s National Security Office led an interagency meeting, deciding to designate cable landfall stations as national security facilities and consider forming a public-private security coordination body.

Given Korea’s high dependency on digital infrastructure and international trade, a disruption to submarine cables would severely impact both economic and national security. Yet public awareness and protection measures remain inadequate. Therefore, cables should be designated as critical infrastructure, and domestic laws should include clearer penalties for intentional damage. Landfall stations require enhanced physical security, and a joint surveillance framework using Navy and Coast Guard assets, supported by underwater sensors and drones, should be implemented to monitor anomalies or suspicious vessel activity in real time.
 
(4) Need for Multilateral Cooperation
 
Multilateral coordination must be institutionalized in advance to ensure rapid, joint responses to cable-related incidents. For example, countries could replicate Denmark’s practice of tracking suspicious vessels—such as Yi-Feng 3—by sharing real-time maritime domain awareness systems. South Korea should pursue memoranda of understanding (MOUs), joint patrol agreements, and intelligence-sharing arrangements with key partners and alliances such as the United States, Japan, NATO, and the EU. A standing international body for information-sharing, investigation, and vessel monitoring—similar to UN sanction monitoring—would also be considered.