Taiwan Expands Cable Patrols as China Linked Threats Put Seabed Security Under Strain

A cable route becomes a daily security mission

Taiwan is running continuous coast guard patrols around vulnerable undersea cable routes, watching 96 blacklisted vessels linked to China and tracking nearly 400 more as it tries to protect the connections carrying its communications. The operation has focused on TP3, a cable deliberately severed in February in a case that brought Taiwan's first criminal conviction for intentionally damaging undersea infrastructure.

On August 28, Captain Juan Chung ching guided a vessel weighing 100 tons along TP3's route in the Taiwan Strait, passing ships moving slowly nearby. His boat, equipped with water cannons and an autocannon, is part of a patrol force that must protect cables while continuing rescues, pursuing smugglers and enforcing maritime law.

As of September 11, 2025, Taiwan regards repeated cable disruptions as part of China's gray zone pressure: actions that force an opponent to spend time, money and manpower responding while stopping short of open conflict. Beijing denies using civilian ships to harass Taiwan and says many cable failures arise from ordinary maritime activity or accidents.

TP3 is one of roughly two dozen cables serving Taiwan and its offshore communities. Its vulnerability has made the seabed a daily security concern, with coast guard crews checking vessel movements, issuing radio warnings and following ships that ignore requests to move away.

For the officers assigned to the route, the challenge is constant attention. A slow vessel near a cable may require investigation, while the same patrol crews remain responsible for emergencies elsewhere at sea.

What happened before the patrol expansion?

Taiwan's concern has grown through several disruptions involving domestic and international connections. The consequences have ranged from prolonged poor service on offshore islands to a prosecution over deliberate damage.

• In 2023, two cable connections to the Matsu islands were cut, leaving about 14,000 residents struggling with degraded internet service.
• In early January 2025, an international cable was damaged near Keelung in northern Taiwan. Authorities investigated the movements of the Hong Kong owned freighter Xing Shun 39.
• In February, TP3 went offline. Coast guard officers escorted the Chinese crewed Hong Tai 58 for investigation within hours.
• Later in 2025, a Taiwanese court convicted Hong Tai 58's captain of deliberately damaging undersea infrastructure and sentenced him to three years in prison.
• On August 28, a patrol along TP3 demonstrated the continuous surveillance now being directed at sensitive cable routes.

The February incident made cable protection a top priority for Juan's unit. Its officers had escorted Hong Tai 58 after the outage, bringing them directly into the investigation that led to the conviction.

Why these connections matter to Taiwan

Submarine fiber optic cables carry well over 95 percent of international internet traffic. They transmit information through fibers laid across the seabed, linking networks in different countries and connecting Taiwan's offshore communities with the main island.

At least a dozen of Taiwan's roughly two dozen cables connect internationally to places including the United States, Japan, South Korea and China. Those connections support an economy driven by exports and central to critical parts of the global semiconductor supply chain.

Chip design, banking, logistics and telemedicine depend on reliable communications. Military coordination and emergency alerts also rely on the wider communications network. Damage can therefore affect both ordinary transactions and services needed during a crisis.

Cable operators can redirect traffic when a line fails. This redundancy means having alternative routes available, much as drivers can use another road when one closes. A single damaged cable rarely produces a complete internet blackout, but repeated cuts can slow connections, increase costs and, in extreme cases, isolate regions.

Matsu's experience in 2023 showed how difficult daily life can become when several links fail. Satellite and microwave connections can keep essential services operating, but their capacity is limited. Higher latency, the delay between sending information and receiving a response, can make video calls, cloud services and some financial transactions lag.

Repairing a submarine cable often takes weeks. A specialized ship must reach the location, find the break, lift the cable to the surface, join the damaged sections and test the connection. Rough seas and safety restrictions in contested waters can complicate every stage.

How the coast guard identifies suspicious movements

Taiwan's coast guard now operates around the clock near TP3 and other sensitive corridors. An alert system flags vessels moving slowly within about 1 kilometer of TP3, while radar station operators examine tracks and help crews identify ships needing closer attention.

Officers begin with radio warnings. If a vessel ignores requests to keep clear, patrol boats can follow it and maintain a visible presence. In cases considered especially risky, cutters maneuver between the ship and the cable route to separate them.

Taiwan is expanding its Submarine Cable Automatic Warning System, a digital fence that helps authorities and cable operators map ships approaching seabed infrastructure. The system combines information about where cables lie with vessel movements so patrols can respond to activity near vulnerable routes.

The watchlist includes 96 boats linked to China, many registered under flags of convenience. This means a ship flies the flag of a country other than the country associated with its ownership or operation. Authorities also track nearly 400 other vessels linked to China, including cargo ships that officials worry could be adapted for military use during a crisis.

Names, flags and routes can change, requiring repeated updates to the watchlist. Security officials say Taiwan shares the live positions of blacklisted vessels and other ships under observation with friendly capitals. Those exchanges also help partners watch ships traveling beyond the Taiwan Strait.

The people and resources behind the patrols

The patrol area has eight boats and nearly 500 officers. Those resources cover cable security alongside rescues, fisheries emergencies, action against smugglers and other maritime law enforcement. Commanders describe the expanded mission as demanding and their workload as stretched thin.

Captain Juan Chung ching said repeated incursions and cable disruptions had weakened public confidence and required Taiwan to respond continually. Explaining why his crews were increasing their presence, he said:

Their incursions have severely undermined the peace and stability of Taiwanese society. We are stepping up patrols in this area, monitoring for any vessels engaging in disruptive or destructive activities.

Lin Fei fan, Deputy Secretary General of Taiwan's National Security Council, pointed to the island's proximity to China and the concentration of cables near busy shipping routes. Cable crossings in these areas are exposed to both anchors dragged accidentally and deliberate interference.

Lin described Taiwan's exposure in these terms:

Taiwan ranks among the top countries facing this issue. We are very close to China and many densely populated submarine cable areas are highly vulnerable to damage.

A disruption at a crowded crossing can affect connections beyond the immediate location. Taiwan's patrol effort therefore concentrates on places where ship activity and cable routes meet, while trying to preserve enough capacity for its other duties at sea.

Two investigations show the enforcement challenge

Hong Tai 58, crewed by Chinese nationals, became the central case in Taiwan's response this year. Authorities said the freighter operated under changing identities. After officers escorted it for investigation following February's TP3 outage, a court found its captain guilty of intentional damage and imposed a prison term of three years.

The judgment was Taiwan's first conviction of this kind. It showed that prosecutors and judges were prepared to handle deliberate cable damage as a criminal act when evidence supported intent.

The January case near Keelung exposed a different problem: reaching a suspect ship and collecting evidence. Chunghwa Telecom notified the coast guard after an international cable was damaged. Taiwan tracked Xing Shun 39, a freighter owned in Hong Kong that at one point sailed under Cameroon's flag, and described its movement as erratic.

Bad weather prevented officers from boarding the ship at sea. Taiwan then asked South Korean authorities in Busan to collect evidence after the vessel arrived. An investigation could therefore depend on cooperation at a foreign port after a ship had left the area of the cable break.

Investigators describe several ways operators can obscure responsibility. Shell companies can conceal ownership, while changes to vessel names, call signs and registration complicate tracking. Some ships deactivate their tracking systems or move slowly near cable routes.

Legal scholars describe this use of civilian operations and uncertain responsibility as civil exploitation lawfare in maritime form. The idea is to use gaps or ambiguity in legal arrangements to create disruption while keeping any connection to a state difficult to trace.

Why cheap ships can create expensive damage

Jenson Chien, who leads a coast guard flotilla in the area, said old cargo vessels and fishing trawlers can inflict serious damage using basic equipment. An anchor or dredging gear can reach infrastructure that is costly to manufacture and install.

Chien described an imbalance between the resources needed to cause disruption and those needed to repair it:

Those ships are like cannon fodder, piles of scrap metal. They employ minimal resources to disrupt and sever our connections, sowing unrest throughout Taiwanese society.

Cables can cost millions of dollars per kilometer to manufacture and lay. A vessel of little commercial value can therefore force a cable operator to undertake expensive repairs while authorities spend additional time and money guarding routes.

Taiwan sees that pressure as part of a wider pattern involving espionage, influence operations, military exercises and cyber activity. Taipei has accused ships linked to China of causing several cable cuts since 2023, an increase from the preceding three years.

Security assessments published in 2025 judge that there is a better than even chance China will continue testing Taiwan's defenses around cable routes. Beijing's Taiwan Affairs Office rejects the accusation that civilian vessels are being used to harass Taiwan. It says Taipei is manipulating claims before the facts are clear and points to routine maritime activity and accidents as common causes of failures.

Why determining intent is difficult

Industry groups record roughly 200 submarine cable faults worldwide each year. Most are caused by fishing equipment or anchors dragged along the seabed. Earthquakes and underwater landslides can also break connections.

A fishing trawl can slice a cable as cleanly as a saw when its angle and the seabed conditions align. Investigators must therefore reconstruct what happened from vessel movements, marks on the cable's outer covering and other physical evidence. Inspection of a suspect vessel may require help from authorities in another country.

Forensic work at depth is difficult, and the frequency of ordinary faults creates room for deliberate operators to deny responsibility. Taiwanese security officials focus on clusters of incidents near sensitive routes, unusual ship behavior and ownership arrangements that are hard to trace when assessing possible coercion.

The United Nations Convention on the Law of the Sea (UNCLOS) sets maritime rights and responsibilities, but provides limited enforcement tools for protecting cables. Infrastructure in international waters is particularly difficult to defend unless officers catch someone damaging it.

The Taiwan Strait combines heavy commercial shipping with competing claims to authority. Taiwan says it can board ships in its contiguous zone, extending up to 24 nautical miles from its coast. A senior official said authorities would seek to board suspect vessels entering that area.

Stopping or inspecting foreign ships near contested waters carries a risk of confrontation. Even after officers reach a vessel, establishing that damage was deliberate remains the hardest part of a prosecution.

The Baltic cases widen the security concern

European governments have confronted similar threats to infrastructure beneath busy seas. In late 2024, two fiber optic cables were damaged in the Baltic Sea, prompting Nordic scrutiny of a freighter owned in China that had traveled from a Russian port.

Around the same period, investigators examined a tanker linked to Russia that was suspected of dragging its anchor across electricity and telecommunications connections. A year earlier, a vessel flying China's flag and traveling from Russia had been tied to a gas pipeline rupture.

NATO subsequently increased protection of critical Baltic infrastructure through Baltic Sentry. The operation uses frigates, patrol aircraft and naval drones to watch cables and pipelines, while retaining the option to stop ships posing a threat.

Officials in Europe and Taiwan describe recurring behaviors: suspect vessels blend into busy shipping lanes, travel at unusual speeds or on unusual courses, and sometimes switch off tracking beacons. Ownership can lead through companies whose connections are difficult to establish.

Western investigators generally reserve direct accusations until they have physical evidence. Even so, activity around cables has prompted concern from Taipei to Helsinki and encouraged closer documentation of ship movements.

Taiwan's blacklist and intelligence exchanges fit that growing practice. European efforts also include boardings where legally permitted, stronger protection for places where cables reach shore and better detection of unusual activity.

What changes are being proposed at sea and in law?

Legal specialists and former officials argue for a broader international response focused on cable routes. Proposals include a maritime security group, clearer financial responsibility and penalties for reckless operations near cables, and greater transparency about ship ownership and tracking.

Supporters want tighter scrutiny of vessels that repeatedly change flags or identities. Faster exchanges of evidence between jurisdictions could help prosecutors connect a ship's activities across several ports and establish the responsibilities of captains and owners.

Governments could also use sanctions or port state controls against companies whose ships repeatedly loiter near cables and refuse lawful inspections. Port state controls are checks exercised by authorities over visiting foreign vessels.

Another proposal is a public reporting system naming persistent offenders, supported by satellite information and cable operator records. Its purpose would be to increase the costs of disruptive behavior by making vessel activity easier for governments and companies to follow.

Taiwan already shares live positions of suspect ships with friendly partners. Officials say those partners help monitor vessels that may travel from the strait to distant ports, where authorities could have another opportunity to collect evidence.

Taiwanese lawmakers have raised penalties for damaging critical infrastructure and are pursuing further legislation specifically addressing submarine cable protection. Alongside the expanded warning system, the government is tightening inspections of foreign vessels within 24 nautical miles.

Protecting cables while preparing for more outages

Navies and companies are developing ways to observe activity below the surface, where radar and ordinary ship tracking offer limited visibility. Proposed seabed sensor networks can detect anchors or equipment scraping near cables.

Autonomous underwater vehicles can patrol routes, check cable condition and assist repairs. New underwater drones can descend thousands of meters, change their tasks during a mission and send alerts ashore in near real time.

Sensor networks marketed under names such as Blue Sentry aim to combine acoustic, magnetic and optical information. In simple terms, they bring together sound, changes in magnetic signals and visual observations to detect activity conventional surface monitoring might miss.

Military leaders in the region say adversaries have attempted to sabotage cables around Taiwan. U.S. Indo Pacific Command has called for stronger intelligence collection to detect and disrupt such attempts, together with investment in alternative connections that keep communications running if several cables fail.

Chinese patents for equipment capable of cutting fortified cables at depth have also drawn attention in trade reporting. Detection and protection technology is developing alongside tools capable of damaging infrastructure.

Taiwan's preparations extend beyond catching suspect ships. Agencies are exploring more varied cable landing locations so connections are less concentrated along vulnerable routes. They are also testing satellite services in low Earth orbit as a backup for essential communications.

Cable operators say they have refined plans for redirecting traffic during repairs. Patrols, warning systems and inspections address the immediate danger at sea; alternative routes and backup connections help keep the economy and public services operating when a break occurs.

Key Points

• Taiwan has expanded continuous patrols near TP3 and other sensitive cable routes, using alerts for vessels moving slowly within about 1 kilometer of TP3.
• Authorities have blacklisted 96 vessels linked to China and are monitoring nearly 400 more, while eight patrol boats and nearly 500 officers also handle other maritime duties.
• A court sentenced Hong Tai 58's captain to three years in prison for deliberately damaging undersea infrastructure after TP3 failed in February.
• The January investigation involving Xing Shun 39 required a request for evidence collection in Busan after bad weather prevented boarding near Taiwan.
• Beijing denies directing civilian ships to harass Taiwan and says accidents account for many cable failures.
• Roughly 200 cable faults occur worldwide annually, mostly involving fishing equipment or anchors, making physical evidence central to investigations.
• Taiwan is combining stronger inspections and legal penalties with intelligence sharing, expanded warning systems, alternative cable routes and satellite backup tests.
• NATO's Baltic Sentry and emerging seabed sensors reflect wider efforts to protect cables and pipelines from disruption.