Countering China’s Subsea Cable Sabotage

China’s Gray-Zone Warfare and the Vulnerability of Subsea Cables

China’s illegal, coercive, aggressive, and deceptive (ICAD) activities pose a mounting threat to global democracies, with subsea cable sabotage emerging as a particularly alarming tactic. These fiber-optic cables, which carry over 99 percent of global internet traffic, form the backbone of modern communication networks—underpinning economic transactions, defense coordination, and digital infrastructure. Disruptions to subsea cables can have far-reaching consequences: these incidents can paralyze financial markets, hinder government operations, and limit access to critical intelligence. As Doreen Bogdan-Martin, Secretary-General of the International Telecommunication Union (ITU), has emphasized, securing these cables is a geopolitical imperative, not just a technical challenge. Without robust protective measures for undersea communications infrastructure, democracies risk falling victim to another destructive form of Beijing’s strategic interference.

Taiwan as a Testing Ground

The Taiwan Strait has become a key battleground for China’s gray zone tactics, where Beijing frequently conducts low-intensity but persistent hostilities to test Taiwan’s resilience. Between January and February 2025, Taiwan experienced four incidents of submarine cable disruptions—three domestic and one international. 

Table 1: Incidents of submarine cable disruptions near Taiwan between January and February 2025. (Source: Created by author.)

In early 2025, the Xingshun 39 (興順39), a Tanzania-flagged vessel controlled by a Chinese entity, deliberately severed subsea cables near Keelung, disrupting Taiwan’s external communications. Investigations revealed that this ship had previously operated under the alias Shunxing 39 while registered in Cameroon—an intentional ruse to avoid detection by maritime authorities. 

Just weeks later, in late February 2025 another incident occurred when the Hongtai 58 (宏泰58)—a Togolese-registered cargo vessel suspected of having a Chinese crew—severed Taiwan’s third subsea cable linking Taiwan and Penghu. A closer examination of its voyage history exposed a troubling pattern: the vessel had frequently changed its name and registration, previously operating under the names Hongtai 168 and Jinlong 389, while cycling through maritime registries in Andorra and Tanzania. This systematic identity manipulation suggests a calculated effort to obscure ownership, evade responsibility and establish a flexible “maritime shadow warrior” network. 

These were not isolated incidents, but rather part of a troubling persistent pattern. According to Chunghwa Telecom, in 2023 cables connecting Taiwan and the Matsu Islands—Taiwan’s off-shore islands near China—were severed 12 times, resulting in repair costs of NTD $96.4 million (USD $2.9 million). [1] While China has consistently denied involvement, the pattern of repeated cable disruptions, which align with its strategy of leveraging civilian assets for military purposes, suggests a concerted effort to degrade Taiwan’s ability to maintain stable digital infrastructure.

The European Front: China’s Disruptions in the Baltic Sea

China’s subsea sabotage tactics extend beyond the Indo-Pacific. In November 2024, two major subsea cables—one connecting Finland and Germany, and another linking Sweden and Lithuania—were damaged within 24 hours of each other. A Chinese bulk carrier, the Yipeng 3 (伊鵬-3), was later discovered operating suspiciously close to both damaged sites. Joint investigations by Danish, German, and Swedish maritime authorities found physical evidence of tampering, raising concerns that Beijing is employing similar gray-zone tactics in both Pacific and European waters.

The Baltic Sea is a critical communication hub for transatlantic fiber-optic cables, supporting NATO’s defense network, financial transactions, and regional security coordination. By targeting these essential lifelines, China is not merely conducting espionage—it is actively testing Europe’s response mechanisms and exploiting weaknesses in international maritime law. If left unchecked, such actions could erode trust in digital security, weaken NATO’s strategic cohesion, and set a dangerous precedent for future cyber-physical hybrid attacks.

Why China Targets Subsea Cables: Strategic Objectives

China’s sabotage of subsea cables serves multiple strategic purposes. First, it tests the resilience of targeted nations, probing their ability to respond to hybrid threats. Taiwan’s repeated cable disruptions have exposed shortcomings in its emergency response and maritime monitoring systems. While the government has taken steps over the past two years to establish a more structured mechanism for detecting and addressing these incidents, gaps remain in enforcement and coordination. Similarly, NATO’s response to the Baltic Sea incidents has highlighted the broader challenges that democracies face in securing shared maritime infrastructure, where jurisdictional complexities and bureaucratic constraints often delay effective countermeasures.

Second, cutting subsea cables disrupts global information-sharing, financial transactions, and military coordination, which weakens the ability of democratic nations to respond effectively to geopolitical crises. By interfering with digital lifelines, Beijing can amplify political instability and economic uncertainty without firing a single shot.

Third, these acts allow Beijing to pursue its geopolitical goals through gray zone warfare, while denying responsibility under seemingly ambiguous circumstances.

Unlike acts of overt military aggression, covert attacks on subsea infrastructure provide plausible deniability, making it difficult for affected states to justify immediate retaliatory measures.

Image: Taiwan Coast Guard personnel prepare to conduct a boarding of the merchant vessel Hongtai 58, suspected of damaging an undersea cable between Taiwan and Penghu (Feb. 25, 2025). (Image source: ROC Coast Guard / CNA)

Taiwan’s Measures to Improve Undersea Cable Security

Recognizing the urgency of the situation, Taiwan has taken decisive steps to enhance subsea cable security through legislative, technological, and enforcement measures. In 2023, the National Communications Commission (NCC, 國家通訊傳播委員會) amended the Telecommunications Management Act (電信管理法) to increase the penalties and fines for damaging communications infrastructure. In 2024, the Ministry of Digital Affairs (MODA, 數位發展部) designated 10 domestic submarine cables—including the Taiwan-Matsu subsea cable—as critical infrastructure, ensuring heightened security measures and government oversight. 

Technological advancements have also played a key role in Taiwan’s strategy. The Submarine Cable Automatic Warning System (SAWS, 自動示警系統), which has been deployed on the Taiwan-Matsu cables and other select international subsea cables, automatically sends alerts to nearby ships and warns them not to drop anchor. 

Following the Xingshun 39 incident, Taiwan’s Coast Guard Administration (CGA, 海洋委員會海巡署) pledged during a session in the Legislative Yuan to implement stricter port state control (PSC) inspections on foreign vessels registered under flag states with a history of false entry declarations. If such vessels enter Taiwan’s 24-nautical-mile contiguous zone, approach restricted waters near Taiwan’s outlying islands close to China, or enter the SAWS warning zone, authorities can board the ship under the Coast Guard Act (海岸巡防法) to verify its Maritime Mobile Service Identity (MMSI) and Automatic Identification System (AIS) for potential violations.

Strengthening Subsea Cable Security: Policy Recommendations

Taiwan’s recent success in reducing cable disruptions through SAWS and Coast Guard patrols should serve as a model for other vulnerable regions. However, to counter these evolving threats, Taiwan and like-minded democracies must continue investing in proactive defenses, international cooperation, and legal deterrents. 

First, Taiwan should expand SAWS installations to additional undersea cables beyond Taiwan-Matsu in order to further increase situational awareness and rapid response capabilities. At the same time, governments must also expedite the establishment of a Coast Guard Aviation Branch (海巡署航空分署), and procure additional unmanned aerial vehicles (UAVs) to improve and enhance surveillance capabilities.

Second, international participation is essential. Taiwan should actively pursue greater collaboration with submarine cable operators and intelligence-sharing networks. In addition to leveraging the Global Cooperation and Training Framework (GCTF, 全球合作暨訓練架構), a key step in this effort would be to expedite Chunghwa Telecom’s participation in the International Cable Protection Committee (ICPC), which works closely with the International Telecommunications Union (ITU) to establish global security standards. Since ICPC membership is not limited to recognized sovereign states, Chunghwa Telecom’s involvement would create valuable opportunities to exchange best practices, strengthen international cooperation, and advocate for more robust multilateral protection mechanisms.

Lastly, legal and diplomatic responses must be strengthened. Taiwan should enact legislation to establish “restricted zones” (限制區) that prohibit vessels from dropping anchors in sensitive areas, thereby protecting submarine cables. Moreover, Taiwan’s democratic partners should continue efforts to classify intentional cable sabotage as a violation of international law, and to impose economic and diplomatic penalties on responsible actors. The United Nations and regional security alliances like NATO must take collective action to deter future gray-zone operations targeting global subsea infrastructure.

Conclusion: Defending the Digital Lifelines of Democracy

The protection of subsea cables is a national security priority. Amid repeated harassment of its subsea cables, Taiwan has steadfastly bolstered its security measures, reduced the risk of disruptions and enhanced the resilience of its digital infrastructure. This progress has been driven by coordinated legislative, technological, and enforcement efforts aimed at safeguarding these critical assets. Taiwan’s recent infrastructure designations and proactive defense measures reflect a strategic shift toward enhanced maritime security. 

However, as China continues to employ covert disruption tactics, democracies cannot afford complacency. To effectively counter these threats, Taiwan and its allies must prioritize resilience, intelligence-sharing, and multilateral coordination. Protecting these vital communication lifelines is essential to upholding a free and open international order. Failure to act will only embolden China to escalate its coercive tactics, further threatening global stability and digital sovereignty.

The main point: To counter Chinese gray zone tactics that target Taiwan’s subsea cables, Taipei needs to expand its implementation of the Submarine Cable Automatic Warning System and expedite the establishment of a Coast Guard Aviation Branch. At the same time, considering that similar cable-cutting incidents have occurred in the Baltic Sea, Taiwan should pursue greater collaboration with submarine cable operators and intelligence-sharing networks. 

[1] Repairing undersea cables is a complex process, which requires a waiting period for repair ships and may also encounter additional delays due to maritime conditions and weather. This leaves Taiwan’s communications infrastructure particularly vulnerable to persistent disruptions.