Submarine cable
Also known as: undersea cable, submarine communications cable, subsea cable, undersea internet cable
Submarine cables are fibre optic cables laid along the sea floor that connect continents and islands, carrying the vast majority of intercontinental internet traffic.
Hundreds of them span the world's oceans, many no thicker than a garden hose in deep water. While people often assume satellites carry global internet, cables move far more data at far lower delay, and damage from ship anchors or sabotage can disrupt entire regions.
Submarine cable, explained at three levels
At home
A submarine cable is like a garden hose for light laid across the ocean floor. Inside are hair-thin strands of glass, and lasers send data down them as flashes of light, billions of times per second. When you video-call someone overseas, your call almost certainly travels through one of these cables, not a satellite, because cables carry vastly more data with much less delay.
At work
Submarine cables are fibre optic systems laid on the sea floor that carry almost all internet traffic between continents, including links between cloud regions, offices, and customers abroad. For a business, they are the hidden backbone behind international calls, software hosted overseas, and global data replication. When one is cut, traffic shifts to other cables, often slowing services for days or weeks until a repair ship fixes it.
At home
The cable itself has a few fibre pairs at its core, surrounded by steel wires for strength, a copper sheath that carries electrical power, and plastic insulation. Near shore, extra steel armour is added and the cable is often buried in the seabed to protect it from anchors and fishing gear. In deep water, it rests on the bottom, roughly as thick as a garden hose, because little down there can damage it.
At work
Light fades over distance, so repeaters spaced roughly every 50 to 100 kilometres amplify the signal, powered by thousands of volts sent from shore. Each fibre pair carries many wavelengths at once, a technique called dense wavelength division multiplexing, giving modern cables hundreds of terabits per second in total. Cables land at landing stations that connect to terrestrial networks. Repairs need one of a limited number of cable ships to grapple the cable, splice it, and re-lay it.
At home
While satellite internet has improved fast, physics favours cables. A single modern cable moves hundreds of terabits per second, more than satellites can carry across an ocean. Low Earth orbit satellites have closed much of the latency gap, but their capacity is shared across huge areas. In my opinion, the best global internet uses both, with cables as the backbone and satellites as backup for islands, remote areas, and emergencies.
At work
Cable risk is concentrated. Many routes share a few landing sites and narrow chokepoints such as the Red Sea and the Strait of Malacca, so one incident can cut several systems at once. Only a few dozen repair ships serve the world, and permits can delay fixes in contested waters. Ownership has shifted toward large tech companies such as Google and Meta, raising geopolitical questions. Cloud architects should map which cables their regions depend on and design failover across diverse routes.
Real-world examples
At home
Aisha's video calls with family in South Africa became choppy for several days. News reports explained that an undersea cable had been damaged and traffic was taking longer routes.
At work
Thomas is a network architect at a Canadian company with offices in Europe and Asia. He chose cloud regions and providers that use different cable routes, so a single cable cut wouldn't knock out international systems.
How it compares
| feature | Submarine cable | Satellite internet |
|---|---|---|
| Capacity | Enormous, many terabits per second | Much lower |
| Latency | Low | Low (LEO) to high (GEO) |
| Share of intercontinental traffic | The vast majority | Small |
| Vulnerability | Anchors, sabotage, earthquakes | Space weather, debris, jamming |
Cables carry the world's data. Satellites fill gaps and add backup.
For analysts
For businesses depending on international connections, I'd ask providers about route diversity. Knowing your traffic doesn't depend on a single cable is a cheap form of insurance.
History & origin
The first transatlantic telegraph cable was completed in 1858, though it failed after a few weeks; a lasting connection followed in 1866, landing at Heart's Content, Newfoundland. Telephone cables crossed oceans from the 1950s. TAT-8, the first transatlantic fibre optic cable, entered service in 1988. Technology companies such as Google, Meta, Microsoft, and Amazon became major cable investors in the 2010s. Cable damage made headlines repeatedly: cuts in the Red Sea in 2024 and 2025 disrupted traffic between Europe, the Middle East, and Asia, and suspected anchor-dragging incidents damaged Baltic Sea cables in late 2024, prompting NATO to boost patrols. In my view, submarine cables are critical infrastructure that deserves far more public attention than it gets.