99% of International Internet Traffic Travels Through Cables on the Ocean Floor. There Are Only 550 of Them.

Key Takeaways

• •550+ active submarine cables carry 99% of all intercontinental internet traffic
• •The first transatlantic cable (1858) took Cyrus Field 4 years and multiple failures. It lasted 3 weeks.
• •Modern cables are 17mm thick (about the diameter of a garden hose) and are laid by specialized ships
• •Sharks bite undersea cables. Google wraps its cables in Kevlar to prevent shark damage
• •Google, Meta, Amazon, and Microsoft now own or co-own the majority of new undersea cable projects

Timeline

There's a thing most people don't know about the internet.

It's underwater.

Not metaphorically. Literally. 99% of all international internet traffic, everything from your emails to Netflix streams to billion-dollar financial transactions, travels through fiber optic cables laid on the ocean floor.

Not satellites. Not radio waves. Cables. Physical cables, thinner than a garden hose, sitting on the bottom of the ocean, sometimes 4,000 meters deep, connecting continents.

There are currently about 550 of these cables in operation worldwide, spanning approximately 1.4 million kilometers. That's enough to wrap around Earth 35 times. They carry data at speeds of up to 26 terabits per second per cable. They are, by any measure, the most critical infrastructure on the planet.

When people say 'the cloud,' they imagine something floating and ethereal. The reality is a cable thinner than a garden hose, resting on the ocean floor 4,000 meters deep, being occasionally bitten by sharks. That cable carries your email, your Netflix, your bank transactions, and your government's classified communications. All of them. Through the same tube.

— Bryte, Root Lab

And almost nobody thinks about them.

The story starts in 1858, with a man named Cyrus West Field.

Field was an American businessman, not a scientist, who became obsessed with laying a telegraph cable across the Atlantic Ocean. Everyone told him it was impossible. The Atlantic is 2,500 nautical miles wide at the point between Ireland and Newfoundland. The ocean floor was unmapped. No ship could carry enough cable. The pressure at the bottom would crush any wire.

Field tried anyway.

The first attempt in 1857 failed when the cable snapped mid-ocean. The second attempt in 1858 succeeded. For three glorious weeks, telegrams crossed the Atlantic in minutes instead of the ten days it took by ship. Queen Victoria sent a message to President James Buchanan. The world celebrated.

Then the cable died. Operators had used excessive voltage trying to increase signal speed, and the insulation degraded. The cable went silent after just 23 days of operation.

In 2008, two cables were cut by ship anchors in the Mediterranean. Seventy-five million people across the Middle East and South Asia lost internet access. Not slow internet. No internet. Two cables. That's how fragile the system is.

— Bryte, Root Lab

Field was financially ruined and publicly humiliated. He spent the next eight years raising more money, improving cable design, and planning another attempt. In 1866, the SS Great Eastern (the largest ship in the world at the time) successfully laid the first permanent transatlantic telegraph cable.

It worked. And it kept working.

That 1866 cable changed the world as profoundly as the internet would 130 years later. Before it, a message from London to New York took 10 to 12 days by ship. After it: minutes. Financial markets synchronized. Diplomacy accelerated. News became real-time across the ocean.

Every undersea cable laid since then follows the same basic principle: put a wire on the ocean floor between two points. The technology has evolved (copper to coaxial to fiber optic, manual laying to GPS-guided cable ships, manual repeaters to laser-powered amplifiers), but the concept is identical to what Cyrus Field did in 1866.

Modern submarine cables are engineering marvels.

The core is a bundle of fiber optic strands, each thinner than a human hair, carrying data as pulses of light. The fibers are wrapped in layers of protection: steel wire armor, copper power conductors (to power the optical amplifiers along the route), waterproofing, and in some cases, Kevlar. Yes, the same material in bulletproof vests.

The Kevlar is partly for strength and partly for sharks.

Sharks bite undersea cables. Nobody is entirely sure why. Some theories suggest the electromagnetic fields attract them. Others suggest they mistake the cables for prey. Regardless, shark bites on undersea cables are a documented and recurring problem. Google specifically announced in 2014 that it wraps its cables in shark-proof Kevlar sheathing.

Cables are laid by specialized ships that cost hundreds of millions of dollars. The ship feeds the cable off the back at a controlled speed while following a precisely mapped route that avoids undersea mountains, seismic zones, and shipping anchor points. The process can take months for a single cable.

When a cable breaks (and they do break, about 100 to 150 times per year globally), a cable repair ship must sail to the break point, grapple the cable from the ocean floor (sometimes from 4,000+ meters deep), bring it to the surface, splice it, and lower it back down. A single repair can take two weeks and cost over $1 million.

Most breaks are caused by ship anchors and fishing trawlers. In 2008, two cables were cut by ship anchors in the Mediterranean Sea near Alexandria, Egypt. The result: 75 million people across the Middle East and South Asia lost internet access. Not slow internet. No internet. India, Egypt, Pakistan, Kuwait, Saudi Arabia, all saw massive disruptions. Two cables. That's the margin.

This fragility should terrify anyone who thinks about it carefully.

The global internet looks resilient on a network diagram. There's redundancy: multiple paths between any two points. If one cable goes down, traffic reroutes through other cables. In theory.

In practice, many regions depend on a very small number of cables. Southeast Asia has limited cable diversity. Africa's western coast is served by a handful of cables, and outages in 2024 disrupted internet across 13 countries simultaneously. Small island nations often have just one or two cables connecting them to the global internet.

Military and intelligence agencies are very aware of this vulnerability. In 2023, the Nord Stream pipeline sabotage raised alarm about the vulnerability of undersea infrastructure to deliberate attack. NATO has increased submarine patrols near critical cable routes. Russia has been observed mapping cable locations with research vessels. China is investing heavily in cable infrastructure along the Digital Silk Road.

The geopolitical dimension is the part that makes infrastructure experts lose sleep.

But the more immediate transformation is economic. Until recently, undersea cables were owned by telecommunications companies (AT&T, NTT, Telefonica, etc.) who sold bandwidth to internet companies. That model is inverting.

Google, Meta, Amazon, and Microsoft now own or co-own the majority of new undersea cable projects. Google alone operates 33 submarine cables spanning over 200,000 kilometers. Meta (with its 2Africa cable) built one of the longest submarine cables ever, circumnavigating the African continent. Amazon connects its AWS data centers with private cables.

Big Tech didn't just build the internet's software layer. They're now building the physical layer too. The companies that carry your data also own the pipes it flows through. The implications for competition, resilience, and geopolitical power are enormous and still poorly understood.

Cyrus Field went bankrupt trying to connect two continents with a copper wire. He was called a fool, a dreamer, a con man. He tried again. And again. And again.

In 1866, he succeeded. The first permanent transatlantic cable carried maybe 8 words per minute.

Today, the cables on the same ocean floor carry 26 terabits per second. Enough to transmit the entire Library of Congress in about 0.5 seconds.

The internet isn't in the cloud. It's in the mud at the bottom of the ocean, wrapped in Kevlar, occasionally bitten by sharks, carrying everything we've ever said to each other.

That's a root worth knowing.

(Sources: TeleGeography Submarine Cable Map, IEEE Spectrum, ICPC (International Cable Protection Committee), Wired, The Atlantic, BBC Future, Google Infrastructure Blog)

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