The Hidden World of Undersea Cables

The internet largely runs beneath the oceans. Here's how it works—and why it matters.

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Where is the internet?

That sounds like rather a strange question, but when most people try to answer it…they can’t. We have a vague sense that the internet must have some physical basis, but, for most of us, our precision doesn’t go much beyond the idea that there are probably a lot of wires and servers and computers somewhere.

Part of the answer lies in sprawling data centers. Most of the time you write an e-mail, for example, odds are pretty good that the data will pass through Loudon County, Virginia. 300 data centers are clustered in a tiny area outside of Washington, DC. They process, by one estimate, 70 percent of the world’s internet traffic every day.

But, in a way, there’s a better answer than data centers. It turns out that most of the internet runs through roughly 500 undersea cables that connect the world, totalling about 900,000 miles—enough to wrap around the entire circumference of the Earth nearly forty times.

As Google’s Jayne Stowell told the New York Times: “People think that data is in the cloud, but it’s not. It’s in the ocean.”

The hidden world of undersea cables is a fascinating one, and entering this unknown world takes us from colonial-era telegraphs to sharks, volcanoes, saboteurs, and spies.

A current map of undersea cables, from TeleGeography.

Early Undersea Cables, Gutta-Percha, and the US Civil War

When the telegraph emerged, rapid communication over vast distances became possible for the first time in history. It ushered in a misplaced optimism. As Charles F. Briggs and Augustus Maverick wrote in 1858: “It is impossible that old prejudices and hostilities should longer exist while such an instrument has been created for the exchange of thought between all nations of the earth.” If only.

But harnessing the power of the telegraph posed a technological conundrum: how can you lay wires across oceans? Various solutions, such as wrapping the copper telegraph wires with tarred cotton or hemp, were unworkable at scale and wouldn’t provide sufficient protection at the bottom of the sea. Then, in the 19th century, European colonists learned about “gutta-percha,” a natural rubber-like substance that comes from trees native to southeast Asia. The Malay people had long used it to make tools, but it proved astonishingly effective at coating telegraph wires. Suddenly, the world could be connected across endless stretches of water.

Just as the technology for the undersea cables was derived from colonial power, so too was the demand for the rapid construction of telegraph networks. As the historian John Tully notes, colonial powers struggled to crush uprisings because they often only learned of them six months later. When an 1857 rebellion threatened the East India Company’s rule, colonists pushed for urgent action. By 1865, “Karachi had a near-instant communications line to London.”

This timespan, from 1857 to 1865, also saw attempts to lay a physical connection between the United States and Europe for the first time. The first attempts, in 1857, failed; the cables snapped repeatedly. But on July 29, 1858, two ships that had been unspooling cables for thousands of miles met in the middle of the Atlantic and successfully spliced the two ends together. The first message was sent just over two weeks later: “Glory to God in the highest; on earth, peace and good will toward men.”

Shortly thereafter, Queen Victoria wrote a short note of congratulations to the US president, James Buchanan. Then, as Duncan Geere writes:

Buchanan shot back a rather more flowery response which said that “it is a triumph more glorious, because far more useful to mankind, than was ever won by conqueror on the field of battle. May the Atlantic telegraph, under the blessing of heaven, prove to be a bond of perpetual peace and friendship between the kindred nations, and an instrument destined by Divine Providence to diffuse religion, civilization, liberty, and law throughout the world.”

His verbose message will have caused headaches for the operators. The reception across the cable was terrible, and it took an average of two minutes and five seconds to transmit a single character. The first message took 17 hours and 40 minutes to transmit.

Grandiose congratulations notwithstanding, the cable was short-lived. It broke after three weeks, on September 3, 1858.

In 1865, then, the only way for news to spread across the ocean was by ship. As I previously wrote, this created an arms race in which faster ships could be used to make money. One Wall Street speculator, James Fisk, decided to capitalize on British ignorance about the end of the US Civil War.

Recognizing that the Confederate Army was likely to soon surrender to General Ulysses S. Grant’s forces, he readied fast boats to cross the Atlantic quicker than the ordinary steamers that carried the mail. Typically, it took ten days for information to cross the Atlantic. If Fisk could travel faster, he could short-sell Confederate war bonds after the surrender had happened. He would know that they were already useless, but hapless investors in London would remain in the dark.

Fisk won the race. For a few days, he was the only person in Europe who knew that the Confederates has lost the war. He sold the useless war bonds to clueless speculators and made millions. (Racing against Fisk to break the news to Europe was a man named Paul Reuter, the founder of the news service that we know, to this day, as Reuters).

One year later, a new undersea cable was successfully laid across the ocean—and the era in which informational edges were measured in days, rather than minutes, drew to a close.

How Cables Are Laid Today—and How to Repair Them

About fifteen years ago, I spent a summer living in Togo, in West Africa. The internet speed was atrocious. I could barely load my e-mail. A year later, I spent several months in Madagascar. The internet was fast. I could stream live radio broadcasts of Minnesota Twins games, listening to hometown baseball from an isolated island off the coast of Africa. By 2018, Madagascar’s internet had become the fastest in Africa—so fast, in fact, that it outpaced average speeds in France, its former colonial power.

Both countries were among the poorest in the world. What accounted for the difference? The reason: Madagascar had become a hub for a major undersea cable.

Today, roughly 99 percent of the traffic on the internet is carried by about 500 submarine cables, the invisible backbone of our digital world. But to lay and repair nearly a million miles of undersea cables, you need specialized ships.

These ships carry not the copper telegraph wires of the past, but cutting-edge fiber optic cables that transmit information near the speed of light. The New York Times describes the manufacturing process:

The cables move through high-speed mills the size of jet engines, wrapping the wire in a copper casing that carries electricity across the line to keep the data moving. Depending on where the cable will be located, plastic, steel and tar are added later to help it withstand unpredictable ocean environments. When finished, the cables will end up the size of a thick garden hose.

That’s it—much of the world runs on a series of slightly oversized garden hoses, filled with protective coverings and bundles of fiber optic cables. And a fully loaded ship can carry up to 4,000 miles of cable at a time.

Here’s a zoomed-in look at today’s robust array of transatlantic cables, via TeleGeography:

Every three days, on average, one of the world’s undersea cables experiences a problem—it gets cut, or caught on something, and needs to be repaired. Cables closer to shore are sheathed in a protective metal cover and buried in the seabed, since there’s far more human activity in those stretches of water. Most of the time, when a cable is cut, fishing boats are to blame, as their anchors or trawlers inadvertently snag a cable and cause a breakage. When that happens, a specialist ship grabs hold of both ends of the cable—even in deep ocean—brings them to the surface and splices them back together, putting the repaired bit in a sturdier casing to protect it from future cuts.

Landfall: 60 Hudson Street

Of course, all of the cables make landfall somewhere—on average, in about five different locations. When they do, the cables are often routed through interchanges, which can sometimes be large buildings filled with a tangled mess of wires and cables. One of them, for example, is in the Tribeca neighborhood of Manhattan, at 60 Hudson Street. This is what the building looks like from the outside:

The building, fittingly, started as a telegraph connection hub for Western Union. It became known as “The Telegraph Capital of America.” As the internet emerged, the building was sold and repurposed into a colocation center, meaning that companies could lease out space to relay data through the building. Now, it’s home to countless wires and servers. Through this one structure, New York is directly connected to the UK and the rest of the EU.

If power was cut to the building, a considerable chunk of internet infrastructure would be at risk, so the building also houses an enormous backup generator, ensuring a steady supply of power even in an emergency. Thousands of people walk by that building every day, unaware that they are passing by one of the crucial pieces of international infrastructure that makes modern life possible.

Photo: Carl Glassman/Tribeca Trib

Sharks, SCUBA Divers and Volcanoes, Oh My!

Back at sea, power cuts aren’t the issue. Instead, there’s another threat: sharks.

This was first reported, by the New York Times, back in 1987:

Slate, which has since reported on the phenomenon, helpfully provides this video of a shark trying to eat the internet:

But don’t worry. Your Netflix isn’t at risk from a Tiger Shark for much longer. That’s because Google—and others—have started coating their fiber cables in Kevlar (the same material used for bulletproof vests) to protect the internet from shark bites.

What they can’t protect it from, however, is the awesome power of Mother Nature. In 2022, the eruption of a volcano—and the ensuing tsunami—in the Pacific island of Tonga severed the cable that connected the island to the rest of the world. For five weeks, the island was cut off from the global internet, isolated because the physical connection had been broken.

Humans are, however, the biggest problem. And it’s not just fishing boats. In 2013, SCUBA-diving saboteurs in Egypt were caught trying to cut undersea cables off the coast.

Geopolitics

That raises the prospect that nation-states could attack undersea internet infrastructure as an act of sabotage, even as a precursor to a war. Undersea cables have become one of the latest potential flashpoints for global conflict, as physical attacks could be used to disrupt the crucial world of digital information flows.

In the 1970s, Operation Ivy Bells was a successful covert effort by the US government to wiretap Soviet transmissions across the depths of the ocean. Using a combination of submarines and specialist divers, the Americans wrapped a custom-made device around the cable that enabled a wiretap. If the cable was raised for repairs by the Soviets, the device was designed to fall off, to avoid suspicion.

These days, the battle over undersea cables is mostly being fought between the United States and China. It’s not just a question of commercial communications, or of spying, but of national security.

For example, ABC News in Australia reports that Taiwan has experienced 27 cable breaks in the last five years — a high rate. While that damage has officially been blamed on Chinese fishing boats dragging their anchors along the seabed, it has raised concerns that any attack by China could be accompanied by an effort to cut Taiwan off from the world by severing underwater cables. A systematic attack on undersea cables could prove disastrous.

As the world becomes more sophisticated and complex, there are more potential failure points than ever before. Every incentive of modern life drives us in an endless quest for ever-greater optimization, an ever-greater reliance on digital infrastructure to underpin modern life. But if we’re not careful, we might engineer a system so complex, so optimized and vulnerable, that the fates of our societies rests too much on a vast, tangled network of shark-proof cables, lurking unseen below the waves.

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