Undersea Cables: The Hidden Fiber of Global Connectivity

Undersea Cables: The Hidden Fiber of Global Connectivity

Beneath the oceans lies a vast network of fiber‑optic cables – the unheralded backbone of the global Internet.  These undersea lines now carry an estimated 95–99% of all intercontinental Internet traffic .  Stretching over 1.2 million kilometers worldwide , they connect continents and countries with astonishing speed.  A single global bank, for example, moves roughly $3.9 trillion in transactions per day over these lines .  In practical terms, almost every email, video stream, stock trade or business call across the globe is relayed through these cables – not satellites or microwave links.  (Indeed, submarine cables carry vastly more data and are far more efficient than satellites .)

*Figure: Map of the world’s submarine cable network.  Undersea cables (red and blue lines) weave a web around coastlines and ocean basins, linking countries and continents .

1. A Brief History: From Gutta-Percha to Gigabits

The history of undersea cables stretches back almost two centuries.  In the 1850s engineers first laid copper telegraph wires under the sea, insulated with natural gums like gutta‑percha.  For example, in 1850 a British company laid a simple wire across the English Channel, and in 1858 the US and UK succeeded (briefly) in linking America and Europe by telegraph .  (The first 1858 Atlantic cable was extremely fragile – it carried a short message in 17 hours before failing .)  By the late 19th century dozens of telegraph cables crisscrossed the oceans, and in 1866 the transatlantic cable was made permanent.

With the telephone age came the next jump.  Mid‑1900s technology replaced telegraph wires with coaxial cables and amplifiers, carrying hundreds of simultaneous phone calls.  In 1956 the first transatlantic telephone cable (TAT‑1) opened, and more followed.  By the 1980s, fiber optics revolutionized the capacity of cables.  The first transoceanic fiber‑optic cable (TAT‑8) began operating in 1988, transmitting tens of thousands of voice channels over thousands of kilometers .  Since then every new generation of fiber cable has had more capacity (often by using more pairs of fibers or wider lightband signals) and better technology.  For example, the 6,600 km MAREA cable (Virginia–Spain) commissioned in 2017 can carry on the order of 160 terabits per second – equivalent to tens of millions of simultaneous HD video streams.

*Figure: Cross-section of a historic 1867 submarine telegraph cable.  Early cables had a single copper conductor (center) insulated with gutta‑percha and wrapped in layers of cloth and tar for protection .

Early cables were extremely fragile.  An 1867 illustration shows a single copper wire coated in gutta‑percha (a rubbery tree sap) inside cloth wrappings .  These early cables often failed after months of use.  Modern cables are far more robust: a fiber‑optic core (thinner than a human hair) is surrounded by multiple layers of tough strength members (steel or aramid fibers), waterproof sheaths and armoring to withstand ocean pressure, abrasion, and fishing gear.  (A modern deep‑sea cable is about 25 mm thick and weighs roughly 1.4 tonnes per km .)  Over time, undersea cable design evolved through new insulators, better amplification and multiplexing, ultimately supporting terabits per second over single cables .  Today’s cables last decades, and operators routinely upgrade the electronics (amplifiers and modems) on each end to squeeze more speed and efficiency from the same fiber.

2. Under the Waves: How These Cables Work

At the core of every submarine cable are optical fibers – hair-thin glass threads that carry data as pulses of light.  A laser at one end sends a modulated light signal down the fiber; at the other end, photodetectors translate it back into electrical data.  To prevent signal loss, each fiber is surrounded by a transparent glass cladding (of slightly lower refractive index) so that light stays confined by total internal reflection.  The fiber bundle is encased in a jelly‑filled tube to block water, then wrapped in layers of steel or aluminum strength members and armoring to protect against crushing forces .  The outermost jacket (often polyethylene) keeps out seawater entirely.  In shallow or coastal waters the cable may have extra thick armor; in the deep ocean, much lighter casing is sufficient.

Along the cable, repeaters (submarine amplifiers) are placed every 50–100 km or so to boost the signal.  These repeaters house electronic amplifiers (typically erbium-doped fiber amplifiers, EDFAs) that convert the weak light signal to electricity, amplify it, and re-inject it into the next fiber segment .  These units require power, which is fed as a constant DC current along thin metal conductors in the cable.  In effect, each repeater is a powered pump sustaining the light beam across thousands of kilometers.  Without repeaters, the practical range of a fiber link would be a few hundred kilometers at most ; the repeater chain allows transoceanic spans of thousands of kilometers.

Laying a cable is a major engineering feat.  Before laying begins, ships and ROVs survey and map the ocean floor along the planned route, looking for obstacles (wrecks, rocks) and choosing stable terrain .  Then a specialized cable‑laying ship deploys the cable.  The massive cable is stored on board on a rotating carousel or in tanks.  Using GPS and dynamic-positioning, the ship slowly moves along the route, feeding the cable out behind it.  In deeper water, the cable is simply lowered to the seabed.  Near coastlines or in shallow areas it is often buried (with a plow or jetting tool) up to a few meters under the sediment for protection .  Throughout laying, sensors monitor cable tension, position and depth to ensure it is laid smoothly without kinks .  In total, installing a single intercontinental cable can take many months and millions of dollars, with multiple ships and crews working in relay.

Once in service, cables are constantly monitored for faults.  If a break occurs (often due to an anchor hit, trawling net, or geological event) special repair ships are dispatched.  The fault is located by sending optical time-domain reflectometry (OTDR) pulses down the fiber to pinpoint the break, then grappling up and recovering that section of cable to the ship.  Technicians splice in a fresh length of cable and re-lay it on the seabed .  Even under ideal conditions, cables do sometimes fail: rough estimates suggest some 100–150 undersea cables are cut or damaged each year, mostly accidentally by fishing gear or ships .  Extensive global coordination (via cable owners and international committees) ensures that redundant paths and backup systems can reroute traffic until repairs are done.

3. Pillars of Power: Geopolitical and Economic Stakes

In our digital age, undersea cables are national assets.  Almost every important bit of global commerce, communication and finance depends on them.  Consider the scope: an estimated $10 trillion of daily financial transactions traverse undersea cables .  A single smartphone video call or e‑mail often bounces across multiple countries via these fibers.  Thus, secure and high‑capacity cable links are as vital as highways or power lines.  Governments, banks, corporations and individuals all rely on these lines for mail, money, news and emergencies.

Strategically, cables confer influence.  Early on, British control of global telegraph cables gave it a major advantage in the 19th century .  Today, cable ownership and landing sites still have geopolitical weight.  For example, many U.S. military and intelligence networks run on American‑owned cables.  In recent years, tech powers have sought to build “cable alliances.”  The G7 nations have openly declared plans to collaborate on secure undersea links .  The U.S., Japan and Australia jointly funded the New Cross‑Pacific cable (EAC) in 2023 to strengthen Pacific connectivity and counter single‑vendor risks .  Likewise, Japan’s “Data Free Flow with Trust” initiative and G7 communiqués stress that cables should preferably connect like‑minded countries .  Conversely, China’s rapid expansion of cable projects (e.g. under its “Digital Silk Road”) is viewed by some as extending its digital influence .  Today only a handful of countries have the infrastructure and know-how to build these systems, so alliance networks matter for global power.  In short, undersea cables have become a silent theater of great‑power competition, shaping economic influence and intelligence access .

Economically, the payoffs are huge.  Better cables (higher capacity and lower latency) mean faster Internet, more cloud computing and new services.  For developing regions, landing a major cable can revolutionize broadband access and investment.  For instance, landing new fiber in coastal cities of Africa or South America often triggers local tech investment and cheaper connectivity.  In Asia and Europe, governments negotiate cable routes and stations to ensure redundancy.  The broadband boom has also attracted non‑telco players: over the past decade Internet companies like Google, Meta (Facebook) and Microsoft have invested billions in their own cables, joining telecom consortia to secure capacity .  Globally, these cables “carry everything from streaming videos and financial transactions to diplomatic communications and essential intelligence” .  The modern digital economy would literally grind to a halt without them.

4. Who’s Behind the Lines: Major Players

Undersea cables are built, owned and operated by a mix of telecoms, tech giants, and a few specialized manufacturers.  Construction and technology:  Almost all submarine cable manufacture (cable design and laying) is controlled by four firms: America’s SubCom, France’s Alcatel Submarine Networks (ASN), Japan’s NEC, and China’s HMN Technologies (formerly Huawei Marine) .  Together these four account for roughly 98% of cable manufacturing and installation .  Smaller builders exist, but large multi‑year undersea projects require enormous expertise, making this a very concentrated industry .

Owners and operators:  Commercial undersea cables are usually funded by consortia of telecom operators and big tech companies.  For decades main telephone carriers (e.g. AT&T, BT, Orange) co-owned cables.  In recent years the major Internet content/cloud companies have jumped in.  As of the early 2020s, Amazon, Google, Meta and Microsoft together own or lease roughly half of all undersea bandwidth .  (These companies typically buy long‑term capacity rights on new cables – for example, Google’s cables include “Grace Hopper” (USA–Europe) and “Equiano” (Africa–Europe), while Meta’s include “Havfrue” (USA–Europe) and “2Africa” around Africa.)  The remaining cables are owned by telecom consortia (often international carriers in Asia, Europe, etc.), governments, or joint ventures.

Landing countries:  The United States and China are each landing hubs, but cables land in dozens of nations.  The U.S., UK, Japan, Singapore, France, Australia and Russia are among countries with major cable stations.  Often smaller nations strive for multiple cable connections to avoid isolation – for example, Taiwan’s Matsu Islands had only two cables and was briefly cut off when they were severed .  Island nations like Tonga or Pacific atolls depend on single cables for all connectivity, so international aid groups and governments have been helping to build new redundant links.

In sum, a global cast of telecom, tech and national actors shape the undersea network.  The three Chinese cable firms (HMN and state carriers) now compete with long‑time Western players.  The U.S. government works closely with SubCom and allied companies on defense-related cables .  In late 2024, China accounted for about 11–18% of the total cable length built in recent years , while U.S./European contractors built the majority.  This ownership mix has strategic implications: for example, U.S. laws now forbid American companies from landing fiber directly into Hong Kong, and U.S. military cables are built only by trusted (U.S. or allied) firms .

5. Under Threat: Security and Resilience

Because cables carry vital data, they are targets for damage or espionage.  Accidental damage is common – anchors, trawler nets, dredging and fishing gear are the leading causes of cable cuts worldwide.  About 100–150 undersea cables are broken each year (mostly near coasts) by such accidents .  Geologic events can also strike.  Earthquakes, landslides and volcanoes occasionally sever multiple cables at once.  For instance, a 1929 Newfoundland earthquake triggered a submarine landslide that snapped transatlantic cables.  More recently (2022) a massive volcanic eruption in Tonga generated seafloor avalanches that damaged both domestic and international cables to the island .  Although natural disasters are relatively rare compared to human mishaps (perhaps 5–10% of faults ), they can knock out connectivity to entire regions.

Beyond accidents, sabotage and espionage are escalating concerns.  State and non‑state actors may deliberately cut or tamper with cables as a form of covert attack.  In 2023, Taiwanese authorities charged the captain of a Chinese-flagged ship with deliberately dropping anchor on a cable near Taiwan .  The island’s coast guard noted multiple recent cable failures they suspect were intentional “gray‑zone” pressure tactics by China .  In another case, attacks by Houthi militants in 2023 damaged cables in the Red Sea, briefly isolating parts of East Africa and Middle East .  In Europe, a 2023 Baltic Sea incident damaged a telecom cable and a gas pipeline simultaneously; officials investigated possible sabotage by foreign ships .  Meanwhile, surveillance is also a worry: intelligence agencies can tap fiber cables to eavesdrop on data.  During the Cold War and again today, there have been accusations (and some evidence) of cable tapping by major powers on foreign cables.  Every new landing of foreign cables is closely scrutinized for backdoors or vulnerabilities.

Legally, protecting cables is tricky.  International law (e.g. the UN Law of the Sea and the 1884 Cable Convention) does require nations to outlaw attacks on cables in their waters , but enforcement is uneven.  If cables are cut in international waters, no single authority can easily punish the saboteur .  In practice, countries increasingly emphasize mutual cooperation: for example, in 2023 the G7 agreed to create new mechanisms for cable security, and NATO opened a London center to coordinate protection of undersea lines .  Industry groups like the International Cable Protection Committee (ICPC) also promote best practices (e.g. marking cable routes on nautical charts).

Given the stakes, redundancy is key.  Most regions now aim to have multiple cable routes.  When one cable fails, traffic can be rerouted dozens of extra milliseconds through another path.  However, truly isolated places (like some islands) can suffer total outages, as seen in Taiwan’s Matsu and Tonga .  Cable owners now factor resilience into planning: they may build new branches, consortia fund alternate spurs, and even use satellite links as temporary bridges.  For example, SpaceX and other satellite constellations can provide stopgap Internet to cut‑off regions, though with much lower capacity than fiber.  (Indeed, analysts stress that fiber cables remain far more efficient and higher‑capacity than any current satellite network .)  In sum, cable security now involves naval patrols, legal frameworks, and technical measures — reflecting how indispensable these lines have become.

6. Looking Forward: Innovations and the Satellite Debate

Undersea cable technology continues to evolve rapidly.  Researchers and companies are pushing the capacity limits of fiber.  Modern cables already use dense wavelength division multiplexing (DWDM), sending dozens of different colored laser signals down each fiber.  Coherent modulation and better error correction have dramatically increased per‑channel speed in recent years.  For instance, new transoceanic amplifiers (like Ciena’s WaveLogic 6) can push 1 terabit per second per wavelength over 12,000 km , a 15% jump in efficiency over prior gear.

Engineers are also adding more fibers to each cable.  Traditional cables had maybe 4 fiber pairs; now new designs often have 8, 12 or even 16 pairs per cable (a concept called spatial-division multiplexing).  By packing more fiber threads into the same sheath, total capacity multiplies.  Figure: compared below shows a traditional 4‑pair cable versus a next‑gen “SDM” cable with 16 pairs – greatly boosting throughput without needing a second ship.

Figure: Spatial-Division Multiplexing: New cable designs pack many more fiber pairs into one cable.  For example, traditional cables (left) had 4 fiber pairs, whereas SDM cables (right) may carry 16 or more pairs for massively greater capacity .

Another frontier is multi-core fiber.  Here, each fiber strand contains not one but multiple separate cores, each acting like its own fiber.  (In effect it doubles or triples capacity within the same glass sheath.)  Early trials of 2‑core and 7‑core optical fibers suggest huge capacity gains, if the adjacent cores’ signals can be managed properly .  Figure: the diagram below illustrates a single-core fiber vs. a multi-core fiber with two separate cores.  Such advances could theoretically double or triple throughput on future cables.

Figure: Multi-Core Fiber:  Traditional fiber has a single glass core (left).  Multi-core designs (right) embed two or more optical cores in one fiber jacket, multiplying data capacity .

Beyond fiber itself, new amplifier and modem technologies promise further gains.  Coherent optical modems and advanced error correction can tweak light signals to squeeze every bit of data through each wavelength.  Labs are exploring things like mid‑infrared lasers and new rare‑earth dopants for amplifiers.  For now, the practical path has been to build more cables: dozens of new routes are under development worldwide.  In 2023–2025 alone, plans were announced for dozens of cables linking Africa, South Asia, the Pacific Islands, and more, often funded by international consortia with government support.  One notable example is the planned India–Middle East–Europe Express cable, intended to bring massive capacity from India through the Middle East to Europe with minimal hops.

What about satellites?  In recent years, “mega-constellations” of low-Earth-orbit (LEO) satellites (e.g. Starlink, OneWeb, Kuiper) have been hyped as a global Internet solution.  While these can provide broadband to remote locations, they cannot replace submarine cables for bulk data.  The physics simply don’t allow equal capacity: an undersea fiber carries terabits per second with a physical beam of light, whereas any satellite beam is gigabits-level at best.  Analysts note that cables remain far more cost-effective and high-capacity .  Instead, satellite networks may play a complementary role – for example, quickly restoring minimal connectivity after a cable cut, or serving ships and planes.  But for the foreseeable future, the world’s data highways will remain under the ocean, not in space.

In the coming decades, we may also see new routes (such as planned Arctic cables taking polar shortcuts, or mesh networks of shorter regional links), as well as better real-time monitoring.  For instance, emerging techniques can use the fibers themselves as seismic sensors, turning cables into distributed earthquake detectors .  Governments and industry are also discussing global cooperative frameworks (via the UN or ITU) to secure cables against attacks and provide rapid repair.  Whatever the innovations, one fact is clear: undersea cables remain the critical arteries of the digital age.  As one expert put it, these cables are “information superhighways” on the ocean floor, and their security and capacity will shape how all of humanity communicates in the future.

Sources: Authoritative industry reports and news from 2020–2025, including the International Cable Protection Committee, TeleGeography and TechCrunch, as well as analyses by think tanks (CSIS, Hinrich Foundation, etc.) and news outlets like Reuters . All facts and figures above are drawn from these recent sources, which detail the history, technology, strategic importance, and challenges of the global submarine cable network.