Your favorite video, email, or video call crosses oceans without you noticing. But it’s not satellites doing most of the work. The real hero is a vast network of fiber-optic cables lying deep under the sea.

More than 95% of international internet traffic travels through these undersea cables. They stretch across the ocean floor, connecting continents and countries. Even though satellites get a lot of attention, they carry less than 5% of global data across oceans.

These cables look surprisingly simple. About as thick as a garden hose, each contains strands of glass thinner than a human hair. Data travels through them as pulses of laser light. These lasers flash billions of times per second, carrying different streams of data at once.

One cable can handle hundreds of terabits per second. That means it carries massive amounts of information, like emails, movie streams, and financial transactions. To keep the light signals strong, the cables have signal boosters spaced along their length.

How Undersea Cables Are Laid and Maintained

Building these cables is a slow, careful process. First, engineers map routes to avoid underwater hazards like mountains and fault lines. Then ships carry huge spools of cable, sometimes hundreds of kilometers long, to lay them on the ocean floor.

The ship moves about six miles per hour while laying cable behind it. That’s about the speed of a light jog. The cable is carefully unspooled and placed on or under the seabed, depending on the depth. Near coasts, cables are buried to protect them from fishing gear and anchors.

Repairs happen when cables get damaged. About 150 to 200 cable breaks occur globally each year. Most are caused by human activity like fishing or ships dragging anchors. Natural causes like underwater earthquakes or currents also play a part.

Fixing a cable is tricky. Repair ships must locate the break, haul up the cable, splice it, and then lay it back down. Weather and international permits can cause delays. Sometimes, entire regions lose internet for weeks if their only cable is cut.

Why Cables Beat Satellites for Internet Traffic

Satellites sound futuristic, but they have limits that cables don’t. Signals to geostationary satellites travel 36,000 kilometers up and back down. This adds delay, which is bad for real-time uses like video calls or online trading.

New satellite constellations in low Earth orbit cut delays by orbiting closer. Still, their total data capacity remains much lower than undersea cables. Even the largest satellite networks can’t match the hundreds of terabits per second carried by a single cable.

Satellites fill important gaps. They provide internet in remote areas, on ships, or in disaster zones. But undersea cables handle the heavy lifting of global internet traffic and offer lower latency.

Growing Risks and Efforts to Protect the Network

Undersea cables are vital to daily life and the global economy. They carry money transfers, cloud services, and communications. But they face growing risks from accidents, weather, and even sabotage.

There have been incidents where volcanic eruptions, such as in Tonga, cut cables and knocked out internet for weeks. Human conflicts also raise concerns. Some countries have been caught tracking or interfering with cables in strategic areas.

To protect this hidden network, nations like the US, UK, and Australia cooperate on new technology. They develop underwater drones to monitor and defend cables. International efforts aim to reduce risks and make the internet more resilient.

The future of global connectivity depends on these cables and how well we protect them. Satellites will help, but the ocean floor remains the backbone of the internet.