If you’ve ever sent an email, streamed a video, or checked your bank account, chances are your data traveled across an undersea cable. The internet, often thought of as ethereal and “in the cloud,” is in fact deeply rooted in the physical world. Data over the internet is not beamed through the atmosphere or by satellites as I’ve found many people believe in my conversations with them about internet infrastructure. Instead, nearly 380 undersea cables stretching over 800,000 miles across the ocean floor quietly and efficiently carry 99% of international communications.
Without these cables, global communication, commerce, and government systems would come to a screeching halt. But despite their critical role, few people are aware of their existence — or their fragility.
The Internet’s Hidden Physical Infrastructure
To the casual observer, the internet might appear to live entirely in “the cloud.” However, that phrase is misleading. The internet’s power and speed come from vast networks of fiber-optic cables buried deep beneath oceans, linking the continents.
These cables are marvels of engineering. They’re made of strands of glass fibers, thinner than a human hair, through which data is transmitted via pulses of laser light. This technology allows for enormous amounts of information to zip back and forth at nearly the speed of light. To protect the delicate glass, the fibers are encased in layers of protective materials like copper, plastic, and steel. This covering enables the cables to withstand the punishing conditions of the ocean floor. Depending on where the cable is laid, it may be further wrapped in layers of tar or sheathed in steel to protect against strong currents or deep-sea fishing equipment.
But while these cables are designed to last for 25 years, their environment is anything but friendly. Currents, earthquakes, rockslides, and human activity can all damage the cables. When a cable snaps, it sets off a race against time, as entire nations can lose their internet connection. That’s where a hidden fleet of cable repair ships comes in.
Installing the Undersea Internet
The construction and maintenance of undersea cables is a precise, grueling job. The process of laying a new cable is akin to a major construction project, often involving months or years of planning to chart out routes that avoid known geological hazards. Once the path is mapped, it can take weeks just to load the cable onto a ship. A vessel like the Durable, used by Google in its projects, can carry thousands of miles of cable at a time.
Each new cable begins life in a factory where glass fibers are bundled together before being encased in protective materials. These miles of fiber-optic cable are then wound into spools the size of trucks and loaded onto ships bound for the open sea.
The cable laying process itself is slow, requiring teams to carefully deposit the cable onto the ocean floor. And the ship moves at a glacial pace — about six miles per hour — as the cable unspools.
For these cables, the deeper, the better. Deep waters provide natural protection, keeping cables away from rocky seabeds and human activity. In these regions, a cable may be no thicker than a garden hose. Close to shore, where the risk of damage is higher, special underwater plows are used to bury the cables beneath the seabed.
A Critical Structure Under Constant Threat
Once a cable is in place, it becomes part of the web of undersea infrastructure that sustains the internet, connecting servers, data centers, and individuals around the globe. But these cables are not invincible. On average, undersea cables break 200 times a year. Most of these breaks are caused by human activity: fishing trawlers that drag anchors across the ocean floor or deep-sea vessels that scrape the cables with equipment.
Natural disasters like earthquakes and tsunamis can also devastate these delicate lines. One of the most infamous instances occurred on March 11, 2011, when a magnitude 9.1 earthquake struck Japan, triggering a tsunami. The tsunami caused extensive damage to undersea cables that connected Japan with the rest of the world.
The crew of the cable repair ship Ocean Link was already at sea, having just completed a repair when the earthquake hit. The crew had to rush to safer waters as the tsunami roared beneath their ship. In the hours and days that followed, cable after cable failed, severing much of Japan’s digital connection to the outside world.
A Dangerous and Delicate Job
On July 29, 1858, two steamships met in the middle of the Atlantic Ocean, connecting a 4,000-kilometer cable for the first time. This thin copper thread brought Europe and North America together via telegraph, heralding a new era of communication. But just weeks later, the cable failed, marking the first in a long line of undersea communications breakdowns. Fast forward to today, and not much has changed.
Repairing undersea cables is an extraordinarily complex and dangerous job, requiring specialized ships and highly skilled crews. When a break is detected, one of the world’s 20 or so specialized repair ships is dispatched to the scene. The process begins by lowering a grapnel —a kind of large hook — into the ocean to retrieve the broken cable from the seabed. Given that some cables lie as deep as 20,000 feet, this can take hours or even days.
Once the broken cable is hauled aboard, the real work begins. Crew members must cut away the damaged section and splice in new cable. Fiber-optic splicing is a task that demands extreme precision, typically carried out in the ship’s cable control room. Engineers must fuse the tiny glass fibers with electric arcs, then encase the spliced section in protective material before lowering the cable back into the sea.
Because undersea cables are laid with minimal slack, each repair introduces additional length to the cable. Over time, these repairs can result in significant stretches of extra cable lying on the ocean floor. To minimize the risk of tangling or snagging, repair crews often tow the new section away from the original cable route before depositing it.
This work is physically demanding and mentally taxing. Crews can spend months at sea, working 12-hour shifts to complete a repair. Conditions are often harsh, with storms and high waves posing constant threats.
“I still get seasick,” says Walt Oswald, a technician with over 20 years of experience. “It’s not for everybody.”
The Costs of Connectivity
Despite the routine nature of cable breaks, repairing them is a costly endeavor. Each undersea cable can cost up to $350 million to lay, and repairs run into the millions as well. While technology companies like Google, Amazon, and Microsoft have invested heavily in undersea cables to ensure the smooth operation of their global services, the financial burden of maintaining the network often falls on telecommunications companies and internet service providers.
These companies are also on the frontlines of geopolitical tensions. The strategic importance of undersea cables makes them a focal point in international relations. In 2018, Australia blocked China’s Huawei from building a cable linking Australia to the Solomon Islands. They cited concerns that the Chinese government could use the cable to infiltrate Australian networks. Similarly, many nations have increased surveillance of their undersea cable networks, fearing that foreign adversaries could sabotage them.
These fears are not unfounded. Over the years, U.S. intelligence officials reported sightings of Russian submarines and spy ships near critical undersea cables. Such activity raises the specter of deliberate attacks on global communication networks, especially during times of geopolitical tension. According to naval expert Henry Sutton, the Russian Navy has unique undersea warfare capabilities designed to target communication cables. And these include special mother submarines carrying smaller underwater drones and even trained Beluga whales. More recently, the Houthis threatened to cut undersea communication cables that run through the Bab el Mandeb chokepoint between Asia and Europe.
What Happens if the Cables Fail?
While undersea cables have built-in redundancies, their failure could still spell disaster for modern society. In a worst-case scenario, the simultaneous loss of multiple cables could sever communication between continents. This would freeze financial markets, halt international banking, and disrupt supply chains.
“When communications networks go down, the financial services sector does not grind to a halt. It snaps to a halt,” warned Steve Malphrus, a former staff director at the U.S. Federal Reserve, at a 2009 cable security conference.
Fortunately, these cables are designed with many backups in mind. The world’s data is distributed across multiple cable routes, and traffic can be rerouted in the event of a break. But as the 2011 Japan earthquake showed, the loss of just a few key cables can bring a country to its knees. Within hours of the quake, Japan lost seven of its 12 transpacific cables, and internet traffic slowed to a crawl as the remaining cables struggled to handle the load.
In 2006, a 7.0 magnitude earthquake off the coast of Taiwan severed eight submarine cables, causing widespread internet outages across East Asia. In 2012, Hurricane Sandy delivered a wake-up call to the industry when it knocked out several transatlantic cables, isolating North America from Europe for hours.
But most disruptions are less dramatic: a ship drops anchor in the wrong place, or a fisherman snags a cable in a trawling net.
The Future of Undersea Cables
Despite advancements in satellite technology, undersea cables remain the fastest, most efficient, and cheapest way to transmit data across the globe. Satellites, while useful for specific tasks like weather monitoring and GPS, simply do not have the capacity to handle the enormous volume of data that flows between continents.
Even the fastest satellites can only carry a fraction of the bandwidth that a single undersea cable can support. Elon Musk’s much-publicized Starlink network is no exception either. It simply cannot match the bandwidth and latency of land-based ISPs.
As more of the world becomes digitally connected, the need for undersea cables will only grow. Cloud computing, artificial intelligence, and the Internet of Things all require fast, reliable data transmission, making these cables more essential than ever. In fact, tech companies have taken matters into their own hands. Google alone has backed at least 14 undersea cables globally, while Amazon and Facebook have invested in others. Until not too long ago, only communication companies laid internet cables.
Emerging economies in Africa, Southeast Asia, and Latin America are particularly dependent on new cable projects to connect their populations to global markets. Earlier this year, Google announced the Humboldt line, the first cable route between South America and Asia-Pacific, linking Chile, French Polynesia, and Australia.
Even as these projects proliferate, the industry faces significant challenges. There are just 20 or so repair ships dedicated to fixing cable faults, and many of them are aging. Some vessels are over 40 years old, and there is little incentive for companies to invest in new ships. The cable repair business operates on very narrow margins. Meanwhile, the crews who maintain these cables are also aging, with fewer young engineers entering the field.
For now, the world’s undersea cables continue to function as the invisible arteries of global communication. While they may be out of sight, these cables are far from out of mind for the engineers, technicians, and repair crews who spend their lives keeping them operational. Without them, our interconnected world would simply cease to function.
