발트해 해저케이블 절단 사태 : 하이브리드 전쟁의 새로운 전장, 그리고 한국에 대한 시사점

The Baltic Sea, a region of strategic importance for European energy and communication networks, has recently witnessed a series of disruptions to its undersea infrastructure. These incidents, ranging from severed communication cables to damaged power lines, have raised significant concerns among European governments and security organizations. While initial investigations pointed to accidental causes, suspicions of deliberate sabotage have persisted, particularly given the geopolitical tensions surrounding Russia and its suspected use of hybrid warfare tactics.

These events have not only intensified NATO and European Union (EU) security efforts but also sent a stark warning to other nations that rely heavily on undersea infrastructure for telecommunications, financial transactions, and military communications. One such country is South Korea, an economic powerhouse in the Indo-Pacific that faces its own set of security challenges. The Baltic incidents highlight vulnerabilities in global undersea networks and serve as a warning for South Korea about how hybrid threats could affect its national security.

The Baltic Sea Cable Disruptions: Accident or Sabotage?

Over the past year, multiple undersea cable disruptions have occurred in the Baltic Sea. One of the most widely reported incidents involved the NewNew Polar Bear, a Hong Kong-registered, Chinese-operated vessel that damaged two subsea data cables and a gas pipeline in the Gulf of Finland in October 2023. Another case involved the Chinese cargo ship Yi Peng 3, which allegedly severed two communication cables between Germany and Finland, as well as Lithuania and Sweden in December 2024. In another instance, Finnish authorities intercepted the oil tanker Eagle S in January 2025, which was suspected of dragging its anchor across the Estlink-2 power cable connecting Finland and Estonia. In the same month, the Latvia-Sweden Fiber Optic Cable was severed, and Sweden seized a vessel regarding the case.

While official investigations have pointed to accidental damage, often caused by commercial ships dragging their anchors along the seabed, security analysts remain sceptical. The repeated nature of these incidents, coupled with reports of Russian naval activities near undersea infrastructure, has led many to suspect a form of hybrid warfare designed to create disruption without triggering a direct military response.

NATO has responded by significantly increasing its military presence in the region. The alliance launched Operation Baltic Sentry, deploying maritime patrol aircraft, naval drones, and surveillance ships to monitor undersea activity. European leaders have also called for stricter monitoring of foreign vessels operating near key undersea infrastructure and have begun investing in new underwater surveillance technology. Despite these efforts, protecting undersea cables remains a formidable challenge. These networks stretch thousands of kilometres along the ocean floor, making real-time monitoring nearly impossible, and legal complexities make it difficult to respond to suspicious maritime activities without definitive proof of wrongdoing.

Implications for South Korea: The Risks of Undersea Infrastructure Disruptions in the Indo-Pacific

South Korea is one of the most digitally connected nations in the world, with its economy, financial markets, and government operations heavily dependent on undersea cable networks. While islands are particularly vulnerable to disruptions caused by severed submarine cables—given their lack of alternative land-based connections—South Korea faces a similar predicament despite being part of the Asian mainland. Due to its geopolitical reality, it effectively functions as a quasi-island state in terms of digital connectivity, as no communication infrastructure can pass through its only land neighbour, North Korea. This structural vulnerability means that any disruption—whether accidental or intentional—could have far-reaching consequences. The recent Baltic incidents highlight how even minor damage to undersea infrastructure can lead to economic and security problems, underscoring the critical need for South Korea to reassess and reinforce its maritime communication resilience.

South Korea’s digital infrastructure is built upon an extensive network of undersea cables that directly link it to the United States, Japan, China, Southeast Asia, and Europe. Furthermore, South Korea’s own islands, such as Jeju and Ulleung, are directly connected to the mainland via undersea cables, making them particularly vulnerable. A key advantage of undersea communication networks is their built-in redundancy, allowing data to be rerouted almost immediately through alternative cables if one is damaged. However, the real vulnerability for islands—or for South Korea, which shares similar constraints—emerges when multiple undersea cables are severed simultaneously, making rerouting either extremely difficult or entirely unfeasible.

While repairing a damaged cable is not prohibitively expensive—typically costing between $2 million and $3 million per repair—the logistical challenges are significant. Restoration efforts can take one to two weeks or longer, during which critical data flows, financial transactions, and national security communications may be severely impacted. The extended disruption period, even if temporary, not only affects economic activity but also presents a strategic vulnerability. During this window, adversaries could exploit weakened communication links to intensify cyber warfare, exert political pressure, or escalate military posturing. This highlights the necessity of a proactive approach to maritime infrastructure security, including early detection mechanisms and contingency plans for rapid restoration.

Much like the Baltic region, the waters surrounding South Korea—particularly the East China Sea and the South China Sea—are highly contested, creating an environment where deliberate disruptions to undersea infrastructure could become a key element of geopolitical competition. The recent case of Taiwan detaining the Chinese vessel Shunxing 39 briefly in January 2025 for suspected damage to undersea cables underscores this growing concern. Notably, Taiwan later sought South Korea’s assistance in further investigating the ship as it headed to Busan, illustrating how undersea cable vulnerabilities transcend national borders and require regional cooperation to address.

The strategic concerns extend into national security as well. The lessons from the Baltic suggest that undersea cable disruptions could be used as a form of hybrid warfare, creating economic, political, and military instability while maintaining plausible deniability. North Korea, for example, has already demonstrated its cyber warfare capabilities, and its willingness to engage in unconventional military tactics raises credible concerns that it could potentially target undersea communication networks as part of its asymmetric warfare strategy. Meanwhile, China has increased its surveillance of undersea networks, leading to speculation that it could use cable disruptions as a coercive measure in a potential Taiwan crisis.

If tensions between the United States and China were to escalate, South Korea could find itself caught in the middle of a geopolitical struggle in which undersea infrastructure becomes a high-value target. The risk of disruptions—whether from accidents, cyber-attacks, or intentional sabotage—underscores the urgent need for South Korea to start to think increasingly proactively to protect its critical infrastructure.

Focus should be on building resilience instead of protecting cables

Protecting undersea cables presents a significant challenge, as it is nearly impossible to continuously monitor infrastructure that stretches thousands of kilometres across the ocean floor. These cables are often located in deep, difficult-to-access waters, making it challenging to detect potential threats, whether from accidental damage, natural disasters, or deliberate sabotage. Increasing naval patrols and deploying autonomous underwater drones can enhance surveillance, but complete protection remains unrealistic due to the sheer scale of undersea networks and the cost of maintaining constant monitoring.

A more effective and sustainable approach may lie in building resilience rather than relying solely on direct protection. This can be achieved through a combination of redundancy in infrastructure and investment in alternative communication technologies. Expanding the number of undersea data cables along different routes can minimize the impact of a single or a single set of cable failure, ensuring that data traffic can be rerouted with minimal disruption. Coordinating with regional allies to develop shared cable networks with overlapping pathways could further strengthen resilience and provide faster repair response capabilities.

However, this approach comes with a significant financial burden. Constructing and laying new undersea cables is a highly capital-intensive process, with costs ranging from hundreds of millions to several billion dollars, depending on the length, depth, and complexity of the route. Moreover, maintaining and repairing these networks requires specialized ships and equipment, further driving up expenses.

In addition to reinforcing cable networks, investing in redundant communication systems is crucial, though also expensive. Satellite-based internet networks, present a viable backup solution. While these systems currently lack the bandwidth capacity of fiber-optic cables, they can still provide essential connectivity for emergency communications, financial transactions, and military operations in the event of cable disruptions.

By adopting a multi-layered resilience strategy, South Korea can mitigate the risks associated with undersea cable vulnerabilities. Strengthening infrastructure through redundancy, enhancing regional cooperation for shared security frameworks, and integrating next-generation communication technologies will collectively ensure that disruptions—whether accidental or intentional—do not paralyze critical national functions. However, these measures demand heavy financial investment, requiring strategic prioritization and careful budget allocation. At the same time, in an era where digital infrastructure is as vital as physical borders, ensuring the resilience of communication networks has become crucial—despite the high cost.