Easy to Attack, Hard to Defend: The Undersea 'Achilles' Heel' That Could Collapse Everything

In May this year, an interesting article was reported in the local Taiwanese media. It revealed that negotiations between the Taiwanese government and Starlink had practically fallen through. Taiwan is among the five regions in Asia without Starlink, alongside North Korea, Afghanistan, Syria, and China. Despite Taiwan betting its future on adopting low-Earth orbit (LEO) satellites, the negotiations ultimately collapsed. While there were regulatory issues, Elon Musk's comment that "Taiwan is an integral part of China" was decisive, and the situation became more complicated amid allegations that the Chinese government pressured Musk not to provide Starlink to Taiwan. Instead, the Taiwanese government is rushing to adopt OneWeb, a European LEO satellite network, and continues negotiations with Amazon. It has even set a goal to launch its own LEO communication satellites by 2027. Why is Taiwan—a highly advanced internet society with a small land area, high population density, and over 99% of its population already using 4G and 5G—clinging so desperately to LEO satellites?

Let's look at an incident that occurred in Taiwanese waters last year. In January 2025, an international undersea telecommunications cable was damaged in the waters north of Taiwan. Taiwanese authorities suspected a cargo vessel named the Shun Xing 39. This vessel, which had been lingering in the waters around Taiwan since December 2024, turned off its identification system on the day the cable was cut and then quietly disappeared toward South Korea. Although communications were rerouted to a backup network, avoiding a large-scale outage, Taiwan took this incident very seriously. A month later, in February 2025, another undersea cable connecting Taiwan's main island and Penghu was damaged, and Taiwan seized the Hong Tai 58, a cargo ship captained by a Chinese national. Prosecutors indicted the captain on charges of intentionally damaging the undersea cable, and the court sentenced him to three years in prison. This was not an isolated incident. According to Taiwanese authorities, there were five undersea cable damage incidents in 2025 alone, and three incidents in each of the preceding two years. Of course, even if not all cable damage is due to deliberate attacks, the story changes when vessels linked to China repeatedly appear in waters close to China.

The scenario Taiwan worries about is clear: China disrupting the internet and communication networks prior to an invasion. Island nations are particularly vulnerable to undersea cable damage. In fact, in the Matsu Islands—which are located just tens of kilometers from the Chinese mainland, are small in size, and have few cables—two undersea cables were damaged in succession in February 2023, causing residents to suffer internet outages for several weeks. Online banking ground to a halt, and card payment terminals stopped working. Some residents had to gather around telecommunications company buildings to find public Wi-Fi, and internet speeds plummeted to just 5% of their usual levels. Taiwanese authorities determined that a Chinese fishing vessel and a Chinese cargo ship had damaged the cables, respectively, but whether it was intentional was never ultimately confirmed.

The problem is not simply a matter of slow internet. Interbank settlements, stock trading, international remittances, cloud servers, military intelligence, and AI training data all travel through these lines—undersea cables. If undersea cables are cut, military command systems, government administrative networks, financial networks, and emergency communication networks could all collapse. As the AI era progresses, data traffic is skyrocketing, making undersea cables even more critical. However, these undersea cables are easy to attack and extremely difficult to defend. Undersea cables are long, thin, and mostly privately owned. Because they are laid across thousands of kilometers beneath the sea, it is difficult to monitor them entirely. Even if a ship drags its anchor over them, it is hard to prove whether it was an accident or a commissioned operation. This is why merchant ships, fishing boats, and oil tankers—rather than warships—always appear in these incidents. It is precisely because of this ambiguity that undersea cables are becoming targets in gray-zone warfare.

China is not the only one employing such tactics. Europe was once thrown into turmoil by an incident attributed to Russia—or at least suspected to be its doing. On December 25, 2024, five undersea cables, including the EstLink 2 power cable connecting Finland and Estonia in the Baltic Sea, were severed simultaneously. Investigations revealed that the Eagle S, an oil tanker linked to Russia's 'shadow fleet,' had dragged its anchor for nearly 90 kilometers, and Finnish prosecutors indicted three crew members, including the captain. However, the court of first instance dismissed the case, ruling that it lacked jurisdiction because the incident occurred outside territorial waters. Although the case ended on an unsettling note, all involved countries suspected Russian involvement. Since then, Europe has begun to view the Baltic Sea as a virtual battlefield for undersea infrastructure. NATO has established a Baltic Sea monitoring mission, while the EU is discussing securing emergency repair vessels for undersea cables and strengthening surveillance systems. The U.S. Congress is also looking into the issue of undersea cable damage, examining both Chinese equipment and the possibility of Russian-style sabotage.

[Jim Risch / U.S. Senate Foreign Relations Committee Chairman (during a hearing in April this year): "More than 95% of global telecommunications traffic travels through undersea cables. Russia has developed not only advanced undersea warfare capabilities but also low-tech means that produce the same effect as dragging an anchor. To end undersea sabotage, we must hold them clearly accountable when such incidents occur."]

Following the hearing, the United States actually tightened regulations on undersea cables containing Chinese equipment. It is also pushing for legislation to protect undersea cables of the U.S. and its allies and to support the construction of new cables that reduce reliance on Chinese-made equipment. Undersea cables are no longer treated merely as communication networks, but as national security assets like military bases and ports.

This issue is not unique to Europe and Taiwan. South Korea also relies heavily on undersea cables for most of its international financial transactions, cloud services, and AI data transfers. In particular, South Korea, the world's largest exporter of memory semiconductors, exchanges vast amounts of data in real time with companies in the U.S., Europe, and Japan during semiconductor design, production, and R&D processes. This means that South Korea's entire industry is highly dependent on undersea cables. In the AI era, the volume of cross-border data transfer is exploding. If data is the new oil, undersea cables are the pipelines that carry it. War no longer begins only on the front lines. The internet could be cut before missiles fly, and financial networks, communication networks, and military command systems could be shaken before a single gunshot is heard. The first scene of a war might not be a massive explosion, but rather a connection failure and the collapse of daily life. This is why the world is now focusing on undersea cables, and why we must closely watch what has unfolded in the Baltic Sea and the Taiwan Strait.

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