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How Undersea Cables Connect the Entire Internet

Almost none of the world's international internet traffic travels by satellite β€” it travels through cables lying on the ocean floor.

Submarine cables carry roughly 99% of intercontinental data

Despite the visibility of satellite internet, the overwhelming majority of international phone calls, video calls, and internet traffic physically travels through fiber-optic cables laid across the seabed.

They are bundles of hair-thin glass fiber, armored for protection

At the core, a submarine cable is a small bundle of optical fibers that transmit data as pulses of light, wrapped in multiple layers of insulation, steel wire, and armor, with thicker armor used in shallow coastal waters where damage risk is highest.

Specialized ships lay cable along carefully surveyed routes

Purpose-built cable ships pay out cable along a route chosen in advance to avoid fault lines, shipping lanes, and existing cables, sometimes burying it under the seabed in shallower areas using an underwater plow.

Cable breaks are repaired by hauling the cable up from the seafloor

When a cable is damaged β€” most often by ship anchors, fishing trawlers, or underwater landslides β€” a repair ship locates the fault, retrieves both cable ends, splices in a new section, and lowers it back down, a process that can take days to weeks.

Big tech companies now build and own cables directly

Historically laid by telecom consortiums, submarine cables are now increasingly financed and even solely owned by major cloud and platform companies that need guaranteed capacity for their own global data traffic.

The biggest real threat is accidental damage, not sabotage

The most common cause of submarine cable faults is unglamorous accidental damage β€” ship anchors and fishing equipment β€” though deliberate sabotage and geopolitical tension around cable routes has drawn growing attention in recent years.

Why the internet still depends on physical cables in 2026

Satellites remain useful for remote or mobile connectivity, but fiber-optic cable carries dramatically more data at lower latency and lower cost per bit than any satellite technology currently can. Redundancy β€” many cables on many routes β€” rather than any single technology switch, is how the industry manages the risk of any one cable failing.

A single country can depend on surprisingly few cables

Some regions and island nations are connected to the rest of the world by only a handful of cables, occasionally even just one or two, which means a single break can cause a significant, sometimes nationwide, slowdown or outage until repairs are completed.

Frequently Asked Questions

How long do submarine cables typically last?

A well-maintained submarine cable is generally designed and expected to operate for around 25 years, though the industry regularly lays new cables well before older ones reach end of life, both for added capacity and redundancy.

Does losing one submarine cable take down the whole internet?

For most well-connected regions, no β€” traffic reroutes through other cables and paths, though there may be a noticeable slowdown. For regions served by very few cables, a single break can cause a serious, visible outage.