When you load a website hosted in another country, you might assume your data travels via satellite. It almost certainly does not. About 99% of all intercontinental internet traffic — including this article you're reading — travels through fiber-optic cables that sit on the ocean floor. These submarine cables are one of the most consequential pieces of modern infrastructure that almost nobody thinks about.
The Basics
Submarine communications cables are bundles of optical fibers, each about the diameter of a human hair, encased in protective layers of polyethylene, steel wire, copper, and a final outer sheath. The complete cable is roughly the diameter of a garden hose — much smaller than most people imagine when they hear "transatlantic cable."
Inside the cable, light pulses (representing digital data) travel through the glass fibers via total internal reflection. Each fiber can carry many terabits of data per second using a technique called wavelength-division multiplexing — different colors of light carry different data streams simultaneously. A single modern cable with multiple fiber pairs can carry tens of terabits per second across an ocean.
The Scale of the Network
As of 2025, there are more than 550 active submarine cable systems worldwide, totaling about 1.4 million km of cable on or under the ocean floor. That's enough cable to wrap around the Earth more than 30 times. The cables connect every inhabited continent and the vast majority of countries with coastlines.
The cables vary widely in age, capacity, and importance. Some short cables connect nearby islands; others span entire oceans. The longest single cable system is the 2Africa cable, which loops around the entire African continent and connects to Europe and Asia — 45,000 km of total length, scheduled for completion in 2024–2025. Major hub regions include the eastern US coast (with many transatlantic landings), the UK, Hong Kong, Singapore, and Marseille.
How Cables Are Laid
Specialized ships called "cable ships" lay the cables. A typical cable ship is about 140 m long with cable-storage tanks holding thousands of kilometers of cable wound carefully to prevent kinks. The ship sails along the planned route at about 5–7 knots (relatively slow), continuously feeding cable into the water through a stern guide. In shallow water near shore, cables are buried 1–3 m below the seafloor using underwater plows. In deep water (>1,500 m), cables typically just rest on the ocean floor, where they're relatively safe from accidents.
Laying a major transoceanic cable takes 3–6 months for the cable-laying phase alone, plus months or years of route surveys, permitting, and manufacturing before that. Total project costs typically run $200–$500 million per cable, depending on length and capacity.
How Cables Break
Submarine cables break surprisingly often — globally, there are about 100–200 cable faults per year. The most common causes are fishing trawlers, ship anchors dragging across cables, and earthquakes. Most breaks happen in shallow coastal waters where human activity is concentrated; deep-water cables rarely break unless damaged by submarine landslides or seismic events.
When a cable breaks, a specialized cable repair ship sails to the location. The ship uses sonar and grappling hooks to find the broken cable ends, lifts them to the surface, splices in new cable, and lowers the repaired section back to the seafloor. The whole process typically takes 1–3 weeks. Most internet traffic gets automatically rerouted through other cables during repairs, so users rarely notice.
Who Owns Cables
Cable ownership has evolved dramatically over time. Originally, cables were built and owned by large consortiums of telecom companies (often state-owned PTTs like the old British Post Office or French France Télécom). Today, the consortium model continues but is increasingly being supplemented and replaced by direct ownership from major tech companies. Google, Meta, Microsoft, and Amazon together now own (alone or in partnership) substantial parts of the global cable network. These four "hyperscalers" justify their cable investments by their enormous internal data traffic needs.
Strategic and Security Importance
Because submarine cables carry essentially all global internet traffic, their security is of enormous strategic importance. The cables are particularly vulnerable in shallow waters where they could be sabotaged, fished out, or cut. Russian naval activities near transatlantic cable routes have prompted NATO countries to invest in cable monitoring and protection. The 2022 explosions on the Nord Stream gas pipelines (separate infrastructure but similar vulnerabilities) heightened concerns about submarine infrastructure security.
Submarine cables also concentrate at specific "chokepoints" where many cables come ashore close together. Major chokepoints include the Suez Canal/Red Sea area, the Strait of Malacca, the English Channel, and the eastern US coast (around Virginia Beach and Long Island). Damage to cables in these chokepoints can have outsized impacts on global connectivity.
Satellites vs Cables
Satellites carry some internet traffic but only a small fraction. Starlink and other low-Earth-orbit constellations have improved satellite internet performance dramatically, but cables remain dominant for high-volume, low-latency intercontinental traffic. Light travels through glass fiber at about 200,000 km/s (about 2/3 the speed of light in vacuum), giving cable a roughly 100 ms round-trip advantage over geostationary satellites for transatlantic connections. Cables also carry vastly more data — a single modern cable system carries more data than all the world's satellites combined.
Notable Cables
Some specific cables of historical or current importance:
- TAT-1 (1956) — the first transatlantic telephone cable, between Newfoundland and Scotland.
- SEA-ME-WE 3 (1999) — Asia's longest cable, connecting Western Europe to Australia via the Middle East and Asia.
- MAREA (2017) — Microsoft/Meta cable between Virginia Beach and Spain, with capacity of 224 Tbps.
- 2Africa (2024–2025) — the world's longest cable system, looping Africa.
- EllaLink (2021) — first direct cable between South America and Europe, bypassing the US.
The Submarine Cable Map
The website submarinecablemap.com shows the global cable network in real-time, updated by TeleGeography. The map reveals both the global reach of cable infrastructure and the specific geographic patterns — high cable density in the North Atlantic, the Pacific Rim, and the Mediterranean; sparser coverage in the Southern Ocean and around Antarctica; and the few but strategically critical cables that connect Africa, South America, and various remote island nations.
Future of the Cable Network
Several trends are shaping the future of submarine cables:
- Higher capacity: New cables with 16+ fiber pairs can carry petabits per second.
- Tech giant ownership: Google, Meta, Microsoft, and Amazon increasingly build their own private cables.
- Diverse routes: New cables avoid the traditional Suez/Red Sea routing for security reasons.
- Arctic routes: Melting Arctic ice could enable Northern Sea Route cables connecting Europe and Asia with lower latency than current paths.
- Quantum networks: Quantum-key distribution over cable is being tested for ultra-secure communication.
The Cable Repair Industry
Behind the global cable network is a specialized industry of cable maintenance and repair operators. About a dozen specialized cable ships operate worldwide, maintained by companies like Global Marine, Subcom, and Alcatel Submarine Networks. These ships are stationed strategically in regions where cable damage is most frequent — the Mediterranean, the Caribbean, the South China Sea, and the major Atlantic and Pacific routes. Repair times have improved dramatically over the decades but still take 1–3 weeks on average. The most challenging repairs are in extreme weather or in waters where geopolitical tensions limit access (the Red Sea has become much harder to operate in since 2023, for example).
Key Facts
- 99% of intercontinental internet traffic travels through undersea cables.
- About 550+ cables totaling 1.4 million km of ocean floor.
- A single modern cable carries terabits per second of data.
- Most cable breaks are caused by fishing trawlers and ship anchors.
- Repair takes 1–3 weeks; rerouting happens automatically.
- Tides on Earth's surface include solid-earth tides — the land itself rises and falls by up to 40 cm.
- Jupiter's moon Io has 100-meter tidal flexing of its solid surface.
- The Mediterranean has tides of only 10–20 cm; the Bay of Fundy has tides over 16 m.
- The Pororoca tidal bore in the Amazon can be surfed for over 10 minutes continuously.
- Earth's day is getting longer by about 2 milliseconds per century due to tidal friction.
The Bottom Line
Tides are caused by the Moon's gravity (primarily) and the Sun's gravity (secondarily), modified by Earth's rotation, ocean basin shapes, and coastal geometry. The result is two high tides and two low tides per day in most places, with dramatic variation in tidal range from less than 30 cm to over 16 m. Tides shape coastlines, ecosystems, navigation, and even Earth's rotation itself over geological time.