Undersea Cables: The Internet's Hidden Backbone

How cables on the ocean floor carry almost all international internet traffic, who builds them, and why they matter for economies and security.

When you watch a video hosted abroad or send an email overseas, the data most likely travels through undersea cables: fibre optic cables laid on the ocean floor. They carry the vast majority of international internet traffic, far more than satellites.

How they work

Undersea cables contain fibre optic strands that carry data as pulses of light. They stretch thousands of kilometres between countries, landing at coastal landing stations. There are several hundred such cables in service around the world.

Who builds them

Historically, cables were built by groups of telecom companies. In recent years, large technology companies like Google, Meta, Microsoft and Amazon have become major investors, building their own cables to connect data centres worldwide.

Economic importance

Global trade in services: finance, software, business services and streaming all depend on cables.
Lower costs: new cables have dramatically increased capacity and reduced the cost of international data.
Development: research by Jonas Hjort and Jonas Poulsen found that the arrival of fast internet via new undersea cables in Africa increased employment, especially in higher-skilled jobs.

India’s cables

India is connected by numerous undersea cables landing mainly in Mumbai and Chennai, with new landing points being developed. India’s IT services industry depends on this connectivity.

Vulnerability

Damage: cables are occasionally cut by ship anchors, fishing, earthquakes or undersea landslides, disrupting internet in affected regions. Repairs require specialised ships.
Security: governments worry about sabotage and espionage. Several incidents of cable damage in the Baltic Sea and the Red Sea from 2023 onward raised concerns.
Concentration: some countries rely on a few cables, making them vulnerable to outages.

The cable cut

An earthquake off the coast damages several undersea cables serving a region. Internet speeds slow dramatically, and some services go offline. Businesses that rely on cloud services and international clients lose work until repair ships fix the cables, which can take weeks. The hidden backbone becomes visible when it breaks.

Thinking the internet travels mostly by satellite

Satellites help in remote areas, but undersea fibre cables carry the overwhelming majority of international data because they offer much greater capacity at lower cost.

Key takeaways

Undersea cables carry the vast majority of international internet traffic.
Big technology companies now invest heavily in new cables.
Cables support services trade, lower data costs and raised employment in Africa.
Cables are vulnerable to damage and sabotage, raising security concerns.