Every day, $22 trillion in financial transactions flow through the 745,000 miles of undersea fiber-optic cables lining the ocean floor. So does 99% of all intercontinental internet traffic — not satellites, not the cloud, but physical cables buried beneath the sea. On April 11, 2026, China’s research vessel Haiyang Dizhi 2 completed a successful test of a device capable of cutting those cables at 11,483 feet below sea level. It is the deepest publicly confirmed cable-cutting capability in the world.
The technology — and why this depth matters
Traditional hydraulic systems work like a bicycle brake: a central pump pushes fluid through long pipes to move mechanical parts at the other end. Powerful, but at 3,500 metres of ocean pressure, long fluid lines are a liability — they rupture, leak, and fail under the crushing weight of the deep ocean.
China’s device uses an Electro-Hydrostatic Actuator (EHA) — technology originally developed for aircraft like the F-35. Instead of one central pump and long fluid lines, each actuator is a self-contained unit with its own pump, motor, and fluid reservoir built in. No long pipes. No single point of failure. Far more precise. Far more reliable under extreme pressure. The device is further protected by a titanium alloy shell and oil-compensated seals that prevent it from imploding under the crushing pressure at 3,500 metres depth.
The cutting element is a diamond-coated grinding wheel running at 1,600 rpm — hard enough to penetrate the steel armour, rubber, and polymer layers protecting a submarine cable, precise enough to cut without disturbing the sediment layer on the ocean floor. Robotic arms with advanced positioning technology ensure accuracy despite limited visibility at depth. The device successfully sliced through 60mm-thick cables in ground trials before the sea test.
The depth advantage is specific and significant. The best known competing ROVs reach 3,000 metres. China just demonstrated 3,500 — clearing that threshold by 500 metres. The device can be integrated with both crewed and uncrewed submersibles, meaning it can operate entirely without surfacing.
What is already happening in shallower waters
The more immediate concern isn’t the deep ocean — it’s the 0–1,500 metre range where cables are armoured and strategically critical. In these shallower zones, a simpler method has been documented: vessels dragging anchors across cable routes. In 2026 alone, Taiwan has reported five cases of cable malfunctions — up from three each in 2023 and 2024. There have been 11 incidents of underwater cable damage in the Baltic Sea since 2023. You don’t need sophisticated deep-sea equipment to cause serious damage. An anchor and a cargo vessel are sufficient.
The EHA device is engineered for deep water. The pattern of real-world incidents is happening in shallow water. Understanding the distinction matters for assessing where the actual risk lives today.
Question — Abhilash Gopinath
Cutting undersea cables would cripple global communications and financial systems — including whoever does the cutting. Would any actor ever deliberately use this capability? To me, the consequences feel beyond nuclear.
Answer
The mutual destruction argument is the strongest deterrent against any large-scale cable cutting campaign. Unlike a nuclear strike, which is geographically contained, severing major undersea cables would collapse global financial markets, internet infrastructure, and supply chains simultaneously. The actor responsible loses alongside everyone else — arguably more so, since modern economies are entirely dependent on the same digital infrastructure.
But the realistic threat isn’t total cable warfare — it’s selective, targeted, and deniable. Cut one cable serving a specific region. Blame a fishing trawler anchor. The pattern of shallow-water incidents already shows this is happening today without any sophisticated technology at all. The deep-sea device adds a new dimension — the ability to cut at depths where repair ships struggle to operate, dramatically extending the window before a severed cable is fixed.
So the honest answer: deliberately taking down the global internet is self-defeating. Targeting specific cables quietly, with plausible deniability, is a different calculation entirely — and one that doesn’t require a single dramatic decision.
Question — Abhilash Gopinath
Is anyone actively monitoring these cables end-to-end — any international body, any consortium of nations? Or is 745,000 miles of the world’s most critical infrastructure essentially unguarded on the ocean floor?
Answer
Largely unguarded — and that’s not an exaggeration. There is no international monitoring body, no equivalent of air traffic control for undersea cables. The cables are owned by private consortiums — including major technology companies and telecoms — and protected primarily by the sheer inaccessibility of the ocean floor.
Some nations maintain cable protection zones near shore where anchoring is prohibited. A handful of specialist cable repair ships exist globally. But across the vast majority of 745,000 miles, detection relies entirely on traffic disruption alerts — meaning you know a cable was cut only after communications start failing. There is no real-time physical surveillance of the ocean floor at scale. The infrastructure carrying the world’s data is monitored only by the data flowing through it.
Question — Abhilash Gopinath
If undersea cables were deliberately cut at scale, could Starlink step in as a backup? Is satellite internet actually capable of replacing what runs on the ocean floor?
Answer
Starlink would help — but it cannot replace undersea cables, and the gap is enormous. Today’s best satellite internet delivers roughly 100–200 Mbps per terminal. Undersea cables carry terabits per second — thousands of times more capacity. The entire global Starlink constellation combined carries a fraction of what a single modern undersea cable delivers.
For individuals in a crisis — yes, Starlink keeps people connected. Email works. Basic communication is possible. But the financial system, cloud infrastructure, bulk data replication, and intercontinental business networks that the world’s economy depends on require bandwidth that satellites simply cannot provide at anything near current scale.
Starlink is a lifeboat, not a replacement. If the cables go down, the internet as the global economy depends on it goes with them. SpaceX is expanding capacity significantly — but the gap between satellite and undersea fiber optic remains vast, and closing it will take years, not months.
Sources: South China Morning Post · Gizmodo · TechRadar · Lowy Institute · Newsweek · The Telegraph via Yahoo News
