The cables beneath
the ocean
Over 600 submarine cable systems spanning more than 1.3 million kilometres carry virtually all of the world's international internet traffic. Here's everything you need to know about them.
What is a Submarine Cable?
A submarine cable — also called an undersea cable or subsea cable — is a cable laid on the sea floor to carry telecommunication signals between landmasses. Modern submarine cables use fiber optic technology: pulses of light travel through glass strands thinner than a human hair, encoding billions of bits of data per second.
Despite the dominance of satellite communications in popular imagination, submarine cables carry over 95% of all international internet traffic. Satellites are used primarily for broadcasting, remote areas, and military applications. For the data-intensive internet — streaming, financial transactions, cloud computing — fiber is unmatched in capacity, latency, and cost per bit.
The first submarine telegraph cables were laid in the 1850s, connecting Europe and North America. The first transatlantic fiber optic cable, TAT-8, entered service in 1988 with a capacity of 280 Mbit/s — laughably small by today's standards, when a single modern cable can carry 400 Tbit/s.
How Submarine Cables Work
At their core, submarine cables are fiber optic cables — bundles of glass fibers through which laser-generated light pulses travel. Each fiber carries multiple wavelengths of light simultaneously using Dense Wavelength Division Multiplexing (DWDM), with each wavelength encoding a separate data stream. A single fiber pair can carry many terabits per second.
The key engineering challenge for long submarine cables is signal loss. Light in fiber attenuates over distance — after roughly 80–100 km, the signal is too weak to read. Submarine cables solve this with repeaters: sealed titanium housings placed at regular intervals along the cable that amplify the optical signal using erbium-doped fiber amplifiers (EDFAs).
Power for these repeaters comes not from batteries but from the cable itself. A high-voltage direct current (typically 3,000–15,000V) is transmitted through a copper conductor running the length of the cable. Power feed equipment (PFE) at the cable landing stations on shore maintains this current continuously.
From the outside in: polyethylene outer sheath → steel wire armoring (in shallow water) → copper power conductor → aluminum water barrier → polycarbonate insulation → steel strength member → fiber optic bundle. Deep-sea sections are thinner and lighter — the enormous water pressure actually helps protect them. Armored sections near shore are as thick as a human arm.
How Submarine Cables Are Built and Laid
Building a major submarine cable system is one of the most complex engineering projects in the world. A trans-oceanic cable costs between $100 million and $500 million, takes 2–3 years from contract to service, and involves specialized vessels, deep-sea robots, and coordination across dozens of countries.
The cable is manufactured in sections at specialized factories — typically in France, Japan, the United Kingdom, or the United States — and stored on enormous reels. Cable-laying ships (cable ships) carry these reels and pay out cable continuously as they follow a pre-surveyed route across the ocean floor.
Route planning is extraordinarily careful: the seafloor is mapped in detail to avoid underwater mountains, volcanic zones, fishing areas, shipping anchor zones, and existing cables. Near shore, cable burial machines dig trenches up to 1–3 metres deep to protect cables from fishing trawls and ship anchors — the two most common causes of cable breaks.
At landing points, the cable comes ashore through a conduit buried in the beach — often at night to avoid public attention — and connects to a cable landing station (CLS), a nondescript building that houses the terminal equipment, power feed, and connections to the terrestrial fiber network.
Who Owns Submarine Cables?
Historically, submarine cables were owned by telecommunications consortiums — groups of carriers that shared construction costs and capacity. This model still exists: cables like SEA-ME-WE-5 are owned by 15+ operators who each fund a portion of the build and receive guaranteed capacity (indefeasible right of use, or IRU) in return.
Since the 2010s, large technology companies have fundamentally changed submarine cable ownership. Google, Meta, Microsoft, and Amazon now own or co-own dozens of cables and are estimated to control the majority of new cable capacity being built. Google's Equiano cable (Europe–Africa) and Firmina cable (US–South America) are recent examples of hyperscaler-owned infrastructure.
This shift has implications for internet resilience and geopolitics. Private ownership concentrates critical infrastructure in the hands of a few companies. Governments — particularly in Europe and the Indo-Pacific — are increasingly funding their own cables for strategic independence.
Why Submarine Cables Break
Submarine cables are remarkably durable — deep-sea sections can last 25 years with minimal maintenance. But they do break, and the consequences are significant.
The most common cause of cable faults is human activity near shore: ship anchors dragging across the seabed, and fishing trawls catching cables. These account for roughly 70% of all reported cable faults. Earthquakes and underwater landslides are the next most significant cause, particularly in the Pacific and around Taiwan, where several major cable failures have been attributed to seismic activity.
When a cable breaks, repairs require a specialized cable repair ship to locate the fault (using time-domain reflectometry), grapple the cable from the seafloor, splice in a new section, and re-lay it. A repair operation typically takes 2–4 weeks and costs $1–3 million. Getting permits to work in territorial waters can take longer than the repair itself.
The 2006 Hengchun earthquake severed 9 cables south of Taiwan, disrupting internet across Southeast Asia for weeks. The 2022 Tonga volcanic eruption cut the sole cable connecting Tonga to the world, leaving the island nation with satellite-only connectivity. In 2024, cables in the Red Sea were damaged, affecting connectivity between Europe and Asia.
Exploring the Submarine Cable Map
GeoCables maps all active and planned submarine cables worldwide, with data sourced from TeleGeography's authoritative cable database. Each cable entry includes its route, landing points, specifications, owner consortium, and current operational status.
The interactive map lets you explore cable routes visually — tracing how data travels from continent to continent, which coastal cities are major landing hubs, and which regions rely on a single cable for their international connectivity. Landlocked and island nations with limited cable access are particularly visible.
Beyond the map, GeoCables provides tools for network engineers and researchers: a cable distance calculator that computes actual routing distance through cables (not straight-line), and a health monitor that tracks real-time performance anomalies on monitored cable corridors.
Explore the map
Browse all 600+ submarine cables, their routes, landing points, and real-time health status.