The Unseen Backbone: Undersea Cables, Geopolitics, and the Race for Reliable Connectivity

<p>At 6:39 on the morning of 5 August 1858, the ship HMS <em>Agamemnon</em> dropped the shore end of a copper wire onto the beach at Knightstown on Valentia Island, off the west coast of Ireland. Days later, on 16 August, Queen Victoria sent a 98-word message of congratulation to President James Buchanan across that wire. It took nearly seventeen hours to transmit, and the cable failed within three weeks after the engineer Wildman Whitehouse pushed too much voltage through it. However clumsy, that message did something no rider, ship or pigeon had ever managed: it carried words across an ocean in a single day. The submarine cable had arrived, and it never left.</p> <p>Today the internet is imagined as something ethereal—the &ldquo;cloud&rdquo;, satellites overhead, signals in the air. The reality is heavier and wetter. Somewhere between 95 and 99 percent of the world&rsquo;s intercontinental data—every transatlantic video call, every trade order between London and New York, most of what you have ever streamed from another continent—travels through fibre-optic cables lying on the seabed, many no thicker than a garden hose. Satellites carry a rounding error by comparison. The romantic idea of a wireless world sits on top of the least wireless infrastructure humanity has ever built.</p> <h2 id="what-a-cable-actually-is">What a cable actually is</h2><div class="ad-unit ad-in-article" aria-label="Advertisement"> <span class="ad-label">Advertisement</span> <ins class="adsbygoogle" style="display:block;text-align:center" data-ad-client="ca-pub-3726833845844946" data-ad-slot="3291553914" data-ad-format="auto" data-full-width-responsive="true"></ins> <script>(adsbygoogle = window.adsbygoogle || []).push({});</script> </div> <p>A modern submarine cable is a marvel of miniaturisation wrapped in brute-force armour. At its heart sit a handful of glass fibres, each finer than a human hair, carrying pulses of laser light. Around them are layers of petroleum jelly, a copper conductor to feed power to the repeaters, steel wire for strength, and an outer sheath of polyethylene. In deep water, where nothing much can reach them, the cables are relatively slender. In shallow coastal water—where anchors drag, trawlers scrape and curious sharks have genuinely been filmed biting them—the armour thickens considerably.</p> <p>Because light loses strength over distance, repeaters are spliced into the cable roughly every 50 to 100 kilometres to amplify the signal. A single transatlantic system can now carry data at rates measured in hundreds of terabits per second. The physical object doing this work would fit comfortably in your hand, and it is sitting in permanent darkness under several kilometres of cold water.</p> <p>Laying one is a slow, deliberate business. A specialised cable ship carries thousands of kilometres of line coiled into vast circular tanks below deck, paying it out over the stern at walking pace—perhaps 200 kilometres a day—while a plough towed behind cuts a shallow trench in the seabed near shore to bury the cable below the reach of anchors and trawl nets. In the deep ocean the cable is simply laid on the bottom. A single crossing can take weeks, and a route survey to find a path that avoids underwater cliffs, active fault lines and existing cables can precede it by years. Each system is a bespoke object, negotiated, surveyed, financed and sunk one careful kilometre at a time.</p> <h2 id="a-history-written-in-broken-wires">A history written in broken wires</h2> <p>The story of these cables is a story of failure survived. Cyrus West Field, an American paper merchant with no engineering background, sank much of his fortune and more than a decade of effort into the first Atlantic crossing. The 1858 cable died within weeks. A second attempt in 1865 snapped mid-ocean and the loose end was lost. Only in 1866 did the <em>Great Eastern</em>, then the largest ship afloat, lay a durable line and recover the 1865 cable as well, finally giving Europe and North America a stable telegraphic link.</p> <p>From there the pattern repeated with each new technology. Telegraph gave way to telephone cables in the twentieth century; the first transatlantic telephone cable, TAT-1, opened in 1956. Then came coaxial systems, and finally the shift to fibre optics in the late 1980s, which multiplied capacity beyond anything the Victorians could have dreamed. Each generation inherited the same essential vulnerability of its ancestors: a thin line, a long way from anyone who could fix it, in water shared by every nation and owned by none. The desperate, expensive persistence that got the first wire across the Atlantic is echoed by the sheer effort behind other engineering firsts, from grand endurance events to feats of stamina like <a href="/story/the-great-london-marathon-a-race-through-time/">the London Marathon</a>.</p> <h2 id="the-politics-of-who-controls-the-pipe">The politics of who controls the pipe</h2><div class="ad-unit ad-in-article" aria-label="Advertisement"> <span class="ad-label">Advertisement</span> <ins class="adsbygoogle" style="display:block;text-align:center" data-ad-client="ca-pub-3726833845844946" data-ad-slot="3291553914" data-ad-format="auto" data-full-width-responsive="true"></ins> <script>(adsbygoogle = window.adsbygoogle || []).push({});</script> </div> <p>A cable is not neutral. Whoever lands it, routes it and taps it holds leverage, and governments have understood this since the telegraph age. During the First World War, one of Britain&rsquo;s opening moves was to cut Germany&rsquo;s transatlantic cables, forcing German traffic onto lines the British could intercept—a lesson in the strategic value of controlling the physical layer that has never been forgotten.</p> <p>The modern version is quieter but no less pointed. Cables are increasingly financed and built by a small number of large technology firms rather than telecom consortia, which raises questions about who really owns the arteries of the internet. Landing stations—the coastal points where cables come ashore—are chokepoints of enormous interest to intelligence agencies, because a tap installed there sees everything that passes. Nations negotiate hard over which routes avoid which territorial waters, and repair ships have on occasion been delayed by governments unwilling to grant them access to sensitive zones. The same logic of contested infrastructure and strategic hardening runs through the wider debate about <a href="/story/the-dangers-of-space-debris/">defending shared orbital and communications infrastructure from deliberate and accidental damage</a>.</p> <h2 id="why-the-sabotage-question-refuses-to-go-away">Why the sabotage question refuses to go away</h2> <p>Most cable damage is accidental and mundane—an estimated two-thirds of faults come from fishing gear and ship anchors, and a smaller share from undersea landslides and earthquakes. The 2006 Hengchun earthquake off Taiwan severed multiple cables and disrupted connectivity across East Asia for weeks, a reminder that geology alone can isolate whole regions.</p> <p>But deliberate damage has moved from theoretical worry to active concern. In late 2024 and into 2025, a cluster of cable and pipeline breaks in the Baltic Sea—involving vessels dragging anchors across the seabed for suspicious distances—prompted several NATO states to launch a monitoring mission and openly discuss the possibility of state-sponsored sabotage. Because the sea floor is dark, vast and lightly policed, attributing such damage is genuinely hard, and that ambiguity is itself a weapon. An adversary who can plausibly deny an anchor-drag enjoys the disruption without the accountability.</p> <h2 id="the-race-to-lay-more-and-lay-smarter">The race to lay more, and lay smarter</h2> <p>The response to all this fragility is redundancy. The engineering answer to a cut cable is another cable somewhere else, so the industry is in a sustained building boom: dozens of new systems are laid every year, deliberately taking diverse geographic paths so that no single earthquake, anchor or hostile act can sever a region entirely. New routes are being pushed through the Arctic and around the coast of Africa specifically to avoid the crowded, contested chokepoints of the Red Sea and the Mediterranean.</p> <p>The same encryption arms race that protects data in transit matters here too, because a tapped cable is only as dangerous as the plaintext it carries—an argument that connects directly to the longer-term work of <a href="/story/quantum-safe-cryptography-explained-future-proofing-your-organizations-data/">future-proofing communications against tomorrow&rsquo;s code-breaking</a>. Faster cable-laying ships, better fault-detection systems that can pinpoint a break to within a few metres, and international agreements on protecting and repairing cables are all part of a slow, unglamorous effort to make the backbone harder to break.</p> <h2 id="fun-facts">Fun facts</h2> <ul> <li>Sharks really have bitten submarine cables; Google added Kevlar-like sheathing to some of its lines partly in response to filmed shark attacks on fibre near the equator.</li> <li>The <em>Great Eastern</em>, the ship that finally succeeded in laying a durable Atlantic cable in 1866, had been a commercial failure as a passenger liner and found its true purpose only as a cable-layer.</li> <li>There are only a few dozen specialised cable-repair ships in the world, and they spend much of their working lives waiting for a fault so they can steam out and haul a cut cable up from the seabed to splice it.</li> <li>The first official transatlantic telegram in 1858, from Queen Victoria to President Buchanan, was so degraded by the failing cable that operators had to send it letter by letter over many hours.</li> <li>A single modern fibre pair can carry more data in a second than the entire 1866 cable could carry in years—the 1866 line managed roughly eight words per minute.</li> </ul> <h2 id="a-closing-reflection">A closing reflection</h2> <p>There is something clarifying about remembering that the most abstract-seeming technology we own rests on the most physical foundation imaginable. We talk about data as if it were weightless, and then a fishing trawler in the Baltic drags an anchor and a country&rsquo;s traffic reroutes halfway around the planet. The genius of the system is that most of us never notice; the fragility is that the people who do notice—the ones watching the anchor tracks and the fault reports—are increasingly worried. The wire Cyrus Field spent a decade fighting the ocean to lay is still, in essence, the wire we all depend on. It is worth knowing it is down there.</p>