Article Series 01 • Fundamentals • Submarine Cables
We live in a "wireless" age — Wi-Fi, 4G, 5G, signals seeming to flow freely through the air. But that impression is a beautiful illusion. In reality, more than 95% of international internet traffic doesn't travel via satellite — it flows through silent cables on the ocean floor. Every international call, every cross-border financial transaction, every webpage loading from an overseas server uses submarine cables.
Global financial markets process more than $10 trillion in daily transactions through submarine cables. If these cables were suddenly cut, it wouldn't just disconnect a region — the global economy could descend into chaos.
A submarine cable looks like a thick rope — about 70mm in diameter in shallow water, just 17mm in the deep sea. But inside is precision engineering, with each layer serving a specific purpose:
The entire cable is laid by specialized cable ships at about 6–10 km/h. Laying a cable connecting two continents can take weeks to months.
The fiber inside cables transmits data as light pulses. A single modern fiber strand can carry tens of Tbps — equivalent to simultaneously streaming millions of 4K movies. A cable may contain dozens of fiber pairs, with total capacity of hundreds of Tbps.
Because light attenuates as it travels through fiber, repeaters are needed every 50–100 km to amplify the signal. These repeaters are powered via the copper conductor in the cable, with electricity supplied from shore stations at each end. A transpacific cable may have over 300 repeaters.
As an island nation, Taiwan's entire digital connection to the outside world depends almost entirely on submarine cables. Taiwan currently has 14 international submarine cables and 10 domestic cables (connecting outer islands). What they carry isn't just Netflix streams or messaging apps — but Taiwan's semiconductor export orders, financial market data, military communications, and government command systems.
But the issue isn't just outages. Submarine cable repairs are extremely time-consuming — the 2023 Matsu cable incident took nearly 50 days to repair. Global cable repair ships are scarce, and if multiple cables are damaged simultaneously, the repair queue becomes very long indeed.
Strategically, submarine cables are the weakest link in Taiwan's "digital resilience." Any action aimed at isolating Taiwan and cutting off its external connections would almost inevitably target submarine cables. This is precisely the core concern that this monitoring site addresses.
Submarine cables are not Cold War relics — they're among the most critical infrastructure of the 21st century, yet they have long received insufficient attention and protection. Their importance operates on three levels:
This is precisely why submarine cables have become ideal targets for "gray zone conflict": the damage is significant, but the perpetrator can claim "accident" and avoid accountability. The next article explains the AIS vessel tracking system and how we use it to detect suspicious behavior.
An ocean-crossing cable is born from a globally scarce fleet of cable-laying ships. These specialized vessels coil thousands of kilometers of fiber-optic cable in giant tanks and pay it out at a few knots along a pre-surveyed route.
In shallow, fishing- and shipping-heavy coastal waters (like the Taiwan Strait), cables are ploughed into a trench and buried to reduce the risk of being snagged by fishing gear or anchors; in the deep sea, where human interference is rarer and burial is costly, cables usually lie directly on the seabed.
Maintenance depends on standby repair ships: once a break is located, a repair ship sails to the site, grapples up both severed ends, splices them, and lowers the cable back to the seabed. The worldwide fleet able to do this is small and often must be dispatched across regions — which is why repairing a single break frequently takes weeks, even months.
The concepts on this page can be verified against these public, authoritative sources:
This page is for research and education; detection signals are leads to investigate, not legal or factual findings. See the methodology.