Submarine Cables: Visible Above the Silicon Shield, the Lifeline Invisible Below

30-second overview: On February 2 and February 8, 2023, the two submarine cables connecting Lienchiang County (Matsu) to Taiwan's main island were severed in succession within six days ¹. Chunghwa Telecom took roughly 50 days to repair the first; the second cable, Taiwan-Matsu No. 2, took a total of 4 months and 23 days to fully repair — Ministry of Digital Affairs Deputy Minister Que Ho-ming said this "exceeded the international average for cable repair" because of "interference from Chinese coast-guard vessels" ². Taiwan's outbound internet traffic relies on submarine cables for 99% of its volume; the 14 active international cables ³ all land at four sites on the main island: Tamsui, Bali, Toucheng, and Fangshan ⁴. In 2024, Chunghwa Telecom quietly opened a fifth landing station in Dawu, Taitung. Locals can only call it the "Building 506" by its street number — a knowledgeable source said this is "a backup external-communication safety net for cross-strait wartime contingencies" ⁵. TSMC's clean rooms are the heroic camera angles above the silicon shield; these 14 lines, buried 1,300 meters down, are the lifeline below that no one sees: they can detach 23 million people from the world without firing a single shot.

"Building 506" Has No Road Sign

Dawu Township, Taitung County. Drive south along Provincial Highway 9, past Dawu Station and a fishing port, and on the roadside stands an utterly ordinary concrete building. No sign, no company logo, no welcome plaque. Locals call it "506" — that's its street number ⁵.

This is the fifth submarine-cable landing station for outbound traffic that Chunghwa Telecom quietly completed in June 2024. It connects to the TPU cable (Taiwan-Philippines-US) — 13,470 km long, 260 Tbps capacity, brought into service October 2025, linking Taiwan to the Philippines and on to the U.S. West Coast ⁶.

But Chunghwa Telecom invited no local officials, no central-government dignitaries to its opening day. The United Daily News later cited a knowledgeable source: this is "a backup external-communication safety net for cross-strait wartime contingencies" — Taiwan's other 14 international cables are concentrated at three points on the west, north, and south coasts facing China. Dawu, Taitung is the first east-coast landing station facing the Pacific, with greater wartime invisibility than any current site ⁵.

📝 Curator's note
Ministry of Digital Affairs Deputy Minister Que Ho-ming told Rest of World: "If you have a cable that isn't on the map, in general it will be cut more often." ⁷ (Cables not on the map tend to get cut less often.) Building 506 is Taiwan's first geographically "concealed" outbound submarine cable, and that line moved from technical advice to physical construction. It tells us this: in Taiwan's 2025 strait dynamics, "not being seen" has itself become a design parameter for infrastructure.

Hair-thin glass, carrying the outbound traffic of 23 million people

Which path does a message from Taipei to San Francisco travel?

Not satellite. Globally, 95% of international internet traffic moves through submarine cables ⁸. Taiwan's 99% of outbound data transmission depends entirely on submarine cables — a conclusion converging from the U.S.-China Economic and Security Review Commission's November 2025 report and the Global Taiwan Institute's June 2025 report ⁹.

The phrase "submarine cable" sounds like a thick pipe, but the optical fiber inside is only as thick as a strand of hair. The body of a trans-Pacific cable is just a few bundles of glass fiber wrapped in insulation, copper tubing, water-proofing, and steel-strand armor. They are plowed into the seabed at a depth of 1.5 to 2 meters, traversing tens of thousands of kilometers across the Pacific trenches at depths reaching 8,000 meters ¹⁰.

Taiwan's 14 active international cables include APG, NCP, FASTER, TPE, EAC-C2C, APCN-2, SJC, SJC2, Apricot, PLCN, China-US, FNAL/RNAL, the Trans-Pacific series, and the newly online TPU — plus SeaMeWe-3, which was retired on December 2, 2024 ¹¹.

Three orders of magnitude apart ¹². As CNA summarized: "Submarine cables transmit at TB units, microwave at GB units, satellite at MB units."

Cheng Ming-tsung, Director-General of the Resilient Infrastructure Department at the Ministry of Digital Affairs, used a more direct analogy: "Wired submarine cables are like the freeway, wireless satellite is the country lane. If both Northern Highways 1 and 2 are completely destroyed, you can't really replace them with the West Coast Expressway and country lanes." ¹³

A Matsu LINE message takes 15 minutes

On February 2, 2023, the Taiwan-Matsu No. 2 cable was suspected to have been severed by a Chinese fishing vessel ¹⁴.

On February 8, 2023, the Taiwan-Matsu No. 3 cable was suspected to have been severed by a Chinese cargo ship dropping anchor. Within six days, both of Matsu's main outbound submarine cables were down.

Over the past 5 years, Matsu has had at least 27 cable breaks in cumulative count ¹⁵: this is no longer news, but the everyday norm of local communications. But two cables down at once was a scenario neither the NCC nor Chunghwa Telecom had handled before. Matsu's microwave backup at the time had only 2.2 Gbps of capacity, against peak demand of around 8 Gbps — far insufficient ¹⁶.

DPP Lienchiang County chair Lee Wen described it on PTS: "A single LINE text message took 15 to 20 minutes to send." ¹⁷ The line was a physical fact, not rhetoric. During those 50 days when Matsu's network was down-throttled to basic communication, the peak season's "Blue Tears" tourists hit checkout systems that worked intermittently, hospitals lost remote consultations, students couldn't get into online classes, elders' digital health-insurance cards wouldn't read.

Chunghwa Telecom emergency-deployed microwave antennas from backup stations in Nantou and Pingtung, expanding Matsu's capacity to 3.8 Gbps (a 76% increase). On March 6, fixed-line internet reopened. On March 31, the first cable, Taiwan-Matsu No. 3, was repaired ¹⁸ — taking about 50 days in total ¹⁹.

But the story didn't end there.

Que Ho-ming later told The Reporter: "The Taiwan-Matsu No. 2 cable took 4 months and 23 days to repair, exceeding the international average for cable repair, in part because of 'interference from Chinese coast-guard vessels.'" ²

⚠️ From 50 days to 4 months and 23 days
Mainstream coverage tends to remember "Matsu disconnected for 50 days." That is the time to fix the first cable — striking, but incomplete. 4 months and 23 days is the real time it took to fix both — adding up to roughly two cable-repair cycles, from the February 8, 2023 break to a full restoration of bandwidth at the end of June. Submarine cable repair isn't "send a boat to splice a knot": you first have to locate the cable with sonar, do seabed operations, lift both ends from hundreds of meters of depth, splice in new fiber, perform thermal-fusion insulation, and lay it back down. And in this case, the cable ship working the accident waters was repeatedly "interfered with" by Chinese coast-guard vessels.

Togolese-flagged, Hong Kong-owned, Fujianese crew, Taiwanese seabed

Two years after the Matsu cable break, 2025 became the year submarine-cable incidents in Taiwan exploded. In a single month, six events occurred. The National Security Bureau's three-year average is 7 to 8 human-caused cable breaks per year ²⁰. The U.S.-China Commission's November 2025 report even noted that between 2019 and 2023, at least 27 cables were damaged in Taiwanese waters ²¹.

These "unidentified vessels" share a common structural pattern.

Shunxing 39, a Cameroon-flagged cargo ship, owned by a Hong Kong company, with 7 Chinese crew. From October 2024, it moved in and out of Taiwanese territorial waters for 3 months, with AIS repeatedly switched off. On January 3, 2025, it severed a section of the TPE international cable in the northeast sea area. Taiwan's Coast Guard intended to board, but failed due to weather. The vessel left port — never entered judicial proceedings ²².

Hong Tai 58, a Togolese-flagged cargo ship, with Chinese crew, called a "Chinese black ship" by the KMT. From February 22 to 25, 2025, it dropped anchor in a no-anchor zone and circled Taiwan-Penghu No. 3 cable. At 3 a.m. on February 25, it severed the cable. Coast Guard boarded the same day and escorted it to Anping Harbor. On April 11, 2025, charges were filed against Chinese captain Wang Yu-liang. On June 12, 2025, the first-instance ruling sentenced him to 3 years and ordered NT$18.22 million in restitution to Chunghwa Telecom — the first case of "new internal waters" judicial jurisdiction ²³.

Togo, Cameroon, Hong Kong, China, Fujian, Taiwan — these six place names overlap with seemingly random regularity in every suspicious vessel. The ship's legal nationality is registered to Togo or Cameroon (because they are "flag-of-convenience states" — cheap registration, lax checks); the actual capital comes from a Hong Kong company; the captain is Chinese; the crew comes from Fujian; the operating waters are Taiwan's. Legally you cannot reach the People's Republic of China, because that's a Togolese-flagged vessel.

Que Ho-ming used a striking English line for Rest of World: "I say this is 'accidental,' and they also said it was 'accidental,' so 'accidentally' all this happened within a week." ⁷ The translation cannot quite capture the rhetoric of the original, but that triple "accidentally" tells you, more directly than any national-security report, how Taiwanese officials view these "accidents."

💡 Did you know?
The National Security Bureau report classifies human-caused damage into four types: (1) mass sand mining exposing and damaging cables; (2) fishing trawlers tearing cables; (3) large cargo ships dragging cables with anchors; (4) Chinese flag-of-convenience vessel cover-ops ²⁴. Taiwan's 2025 "blacklist" identifies 52 Chinese flag-of-convenience vessels, of which 15 pose a high threat, 4 a moderate threat, and 10 a "certain degree of threat" ²⁵. But the "blacklist" is a Taiwanese administrative classification, not a judicial conviction — that is the physical meaning of the "gray zone": you can see it, but you cannot prove it.

China tries to bypass Taiwan, finds it can't

April 21, 2017. Google, Facebook, and a company called Pacific Light Data Communication (PLDC) filed an application with the U.S. FCC to lay a trans-Pacific cable called PLCN (Pacific Light Cable Network). The designed route: U.S. – Hong Kong – Taiwan – Philippines ²⁶.

PLDC's parent company was China's Dr. Peng Telecom.

Trump had not yet taken office. China-Hong Kong cables were still routine engineering for the U.S. side.

In June 2020, U.S. Team Telecom (an inter-agency review body) recommended that the FCC partially deny PLCN: refuse the U.S.-Hong Kong direct link, refuse Chinese shareholder participation — but preserve the U.S.-Taiwan and U.S.-Philippines segments ²⁷. Google and Facebook withdrew the original application and refiled (no Hong Kong segment, no Chinese shareholders). In January 2022, the FCC approved commercial operation of PLCN's U.S.-Taiwan and U.S.-Philippines segments.

From that moment, "bypassing Hong Kong" became the new political principle of Pacific cable construction. China's original plan to enter trans-Pacific cable projects through Dr. Peng was cut off, and subsequent cables like HKA, HK-G, and Bay-to-Bay Express were rejected or rerouted ²⁸.

Chunghwa Telecom Chairman Chien Chih-cheng summarized this turn for CNA: "Cables led by the U.S. side avoid landing in Hong Kong as much as possible, and more cables now land in Taiwan." ²⁹ "Future international cable deployments will avoid politically sensitive segments where permits are hard to obtain, and equipment will be required to de-Sinicize the supply chain."

This is, paradoxically, a windfall for Taiwan. Hyperscalers (Google, Meta, Microsoft, Amazon), which might otherwise have routed cables around Taiwan, now choose Taiwan as their Asia-Pacific hub:

• Google: FASTER (2016) + PLCN (2022) + TPU (2025) + Apricot co-investment + Topaz (2024)
• Meta: Apricot + Bifrost + Echo + the Candle project (announced October 2025, online 2028, the largest Asia-Pacific capacity) ³⁰
• Microsoft + AWS: co-investing in AUG East with Chunghwa Telecom (NT$2.9 billion, completion 2029) ³¹
• Chunghwa Telecom also invests NT$4.6 billion in E2A (online second half of 2028)

In the short run, this density makes Taiwan a cable hub. But the flip side is the same fact: when you become an unbypassable point, you become a target.

The freeway is bombed; back roads can't pick up the slack

After the Matsu break, the Ministry of Digital Affairs accelerated the rollout of backup systems.

Microwave backup went from 2.2 Gbps to 3.8 Gbps, expanded again in 2025 to 12.6 Gbps ¹⁶. Low-orbit satellite backup chose OneWeb (Eutelsat), not Starlink — by the end of June 2024, OneWeb signal covered Taiwan's main island plus Kinmen, Matsu, and Penghu, and by the end of 2024, 700 user terminals + 70 base-station backhaul links were complete ³².

The choice of OneWeb over Starlink was political. Musk's restrictions on Starlink service to Ukraine alerted Taiwan: "political reliability" of satellite backup is as important as technical capacity. But OneWeb capacity falls far short of Starlink — that is the cost of "distributing trust."

In Q1 2025, Chunghwa Telecom introduced mid-orbit satellite (SES) commercial service as the third layer of backup, beyond microwave and low-orbit satellite ³³.

But the physical fact of three orders of magnitude difference doesn't change. To rephrase Cheng Ming-tsung's freeway analogy: if all 14 international cables go down, Taiwan won't become a "silent island" — but it will throttle down to "basic communication": LINE text gets through, but Netflix, cloud work, AI model calls, and cross-border financial settlement all stall.

Feng Kai-ming, professor of electrical engineering at National Tsing Hua University, gave PTS a chilling line: "If the PLA wants to attack Taiwan, just attacking our submarine cables would very easily isolate Taiwan from the world." ³⁴ Ting Shu-fan, emeritus professor at NCCU's Graduate Institute of East Asian Studies, added: "Just by using precision-strike weapons against the four international cable landing stations, you could destroy the entire network system in one go." ³⁵

📊 Data: The U.S.-China Economic and Security Review Commission's November 2025 report estimates: if China cuts all of Taiwan's cables, Taiwan's daily economic loss is US$55.6 million (~NT$1.73 billion) ³⁶. The figure is conservative, because it only counts the direct loss from interrupted internet services — it doesn't include the suspension of semiconductor exports, freezing of cross-border financial transactions, or the cascade of multinational corporations losing connection to their Taiwan branches.

A ship for 22 days, a ship at NT$800,000 per day

How long does it take to repair a broken submarine cable?

January 2025 TPE international cable incident: Japan's KDDI Ocean Link arrived in Taiwan on January 13 and completed repairs on January 20 — 7 days ³⁷.

2023 Taiwan-Matsu No. 2 cable: 4 months and 23 days.

What's the difference? International cables are prioritized over domestic cables (because of consistent shareholder structure and ship fleets), and the Taiwan-Matsu No. 2 repair in 2023 ran into "interference" from Chinese coast-guard vessels.

Globally there are only about 60 cable ships, of which roughly 50 have repair capability and 22 are dedicated to repair ³⁸. Taiwan owns no cable ship of its own; it has joined two repair-ship zones: YOKOHAMA and SEAIOCMA (Southeast Asia and the Indian Ocean), with a total of 6 cable ships that can be dispatched to Taiwan ³⁹. The ships' nationalities are Japanese, Korean, Singaporean, and Chinese (Hua Hai Long); Taiwan has none of its own.

A single repair runs NT$10–20 million; a cable ship's daily charter is around NT$800,000 ⁴⁰.

Why doesn't Chunghwa Telecom build its own repair fleet? Chien Chih-cheng's answer is direct: "Building our own repair-ship team probably wouldn't be economically viable." ⁴¹ Que Ho-ming added another structural reason: "Microwave and satellite backup are already 100% government-funded. Submarine cables are inherently profitable, so additional government funding for them would run counter to the original direction of Chunghwa Telecom's privatization." ⁴²

Chien Lien-kuei, professor of harbor and river engineering at National Taiwan Ocean University, leaves a little room: "Maybe with some accumulated experience, the next step could be to start with near-shore work, taking on repairs ourselves." "There probably aren't more than three [vendors with repair capability]." ⁴³

The other half of the silicon shield, or — the soft spot

Foreign media's favorite metaphor for Taiwan's digital sovereignty is the silicon shield: a Chinese attack on Taiwan would paralyze TSMC and collapse the global supply chain, so the U.S. will intervene.

But submarine-cable logic is asymmetric.

The silicon shield triggers U.S. intervention; the cable gray zone does not. A Togolese-flagged cargo ship dropping anchor in Taiwan's no-anchor zone and severing a Taiwan-Penghu No. 3 cable does not, under international law, constitute an "armed attack." It does not trigger the defense-cooperation clause of the Taiwan Relations Act. It does not send the Seventh Fleet to sea. The cumulative effect of 7 to 8 cable breaks per year by Chinese flag-of-convenience vessels can slowly strangle Taiwan's outbound communications without being deemed an act of war.

British Foreign Policy columnist Elisabeth Braw analyzed it for PTS: "The Matsu disconnection event was very likely China rehearsing the blockade of Taiwan's outbound communications, testing how the Taiwanese government responds. This is a form of harassment, and a textbook gray-zone strategy." "China can of course say it was just a fishing boat, just a merchant ship — there were no warships, no military strikes against Taiwan." ⁴⁴

Journalist Samanth Subramanian, author of The Web Beneath the Waves, summed it up in colder English: "Were a foreign power to snap those fifteen international cables, Taiwan — the West's buffer against China, and the semiconductor factory to the planet — would be unmoored from the world it needs and the world that needs it." ⁴⁵

The silicon-shield metaphor holds, but only halfway. Submarine cables are more like a soft spot, not a shield.

The "Submarine Cable Seven Laws," the Hong Tai 58 judicial first, and one repair of 4 months and 23 days

Still, Taiwan has done some things in these 24 months.

On April 28, 2025, the Pingtung District Prosecutors Office established the country's first "Submarine Cable Safety Joint Defense Regional Response Platform" ⁴⁶. On September 8, 2025, the Executive Yuan passed amendments to the "Submarine Cable Seven Laws." On December 16, 2025, the Legislative Yuan completed the third reading ⁴⁷:

• Intentional sabotage of submarine cables: up to 7 years' imprisonment plus NT$10 million fine
• Negligent acts also penalized
• Offending vessels can be seized directly
• Violation of vessel-identification requirements: up to NT$10 million fine

The Hong Tai 58 case, in which Chinese captain Wang Yu-liang was sentenced in June 2025 to 3 years plus NT$18.22 million in restitution, with the second-instance ruling upholding the 3-year sentence, is the "first case of new internal waters judicial jurisdiction" — Taiwan's first clear judicial victory at the boundary between "gray zone vs. law" ⁴⁸.

The Control Yuan in 2025 passed an investigation report (by Yeh Yi-jin and Lai Ting-ming) that affirmed the Submarine Cable Seven Laws but called for refinements ⁴⁹. In 2025, Chunghwa Telecom added the Taiwan-Penghu-Kinmen cable and the Taiwan-Matsu No. 4 (200 Gbps, completion June 2026). Microwave backup expanded to 12.6 Gbps; OneWeb user terminals were fully deployed.

But none of this changes one physical fact: globally there are only 60 cable ships, Taiwan can dispatch only 6 of them, and a single cable repair takes on average 7 to 30 days; if seas are rough or someone is "interfering," that stretches to 4 months and 23 days. The outbound-communications lifeline of Taiwan's 23 million people hangs on those 14 strands of hair-thin glass fiber, buried 1.5 meters beneath the seabed.

✦ "If you have a cable that isn't on the map, in general it will be cut more often." — Que Ho-ming ⁷

That is why Building 506 has no signboard.

Further reading

• The Reporter: a decade of rescuing investigative reporting from a line item to a public good (報導者) — another case study, alongside this article, on Taiwan's civic society and the credibility of infrastructure since 2015
• Taiwan new media art (台灣新媒體藝術) — the digital cultural infrastructure also carried by the internet beneath the cables
• Social movements and civic participation (社會運動與公民參與) — the larger context for the Submarine Cable Seven Laws legislation, local response platforms, and civil-society pressure
• justfont and the development of Taiwanese typography — another axis demonstrating the dimension of "cultural infrastructure"

References