The Internet is powered by more than 500 cables on the ocean floor.
A network of expensive cables, which have evolved into the essential connectors of our online life, is laced throughout the frigid depths of the world’s seas.
In London, there is a concert. You are observing it live from your Atlanta home. A network of subsea cables draped across the chilly, dark contours of the ocean floor allows for the transmission of images and sounds at the speed of light through thousands of miles of glass fiber that are as thin as human hair.
These wires, which are only little thicker than a garden hose, are technological marvels. The transatlantic cable known as Amitié, which was just finished and funded by Microsoft, Meta, and others, is the fastest and has a 400 terabit per second data transfer rate. If you’re fortunate enough to have high-end gigabit service, that’s 400,000 times faster than your home broadband.
And yet, subsea cables are also low-tech; they are covered in tar and unspooled by ships using essentially the same technique that the first transatlantic telegraph cable was laid in the 1850s. New Jersey-based SubCom, a manufacturer of subsea cables, began as a rope business with a factory near to a deep-water port for convenient ship loading.
Subsea cables, which transmit more than 99% of traffic between continents, are the workhorses of global trade and communications, even as satellite linkages are becoming more significant with orbiting systems like SpaceX’s Starlink. As the internet penetrates to every corner of the world and our lives, TeleGeography, an analytic group that analyzes the industry, is aware of 552 existing and proposed subsea cables.
You undoubtedly already know that the internet is controlled by tech behemoths like Meta, Microsoft, Amazon, and Google. Because they manage hundreds of data centers containing millions of servers, they are referred to as “hyperscalers”. They increasingly control the central nervous system of the internet, which you may not be aware of.
“The whole network of undersea cables is the lifeblood of the economy,” said Alan Mauldin, an analyst with TeleGeography. “It’s how we’re sending emails and phone calls and YouTube videos and financial transactions.”
Two thirds of traffic comes from the hyperscalers, according to Telegeography. And the data demands of hyperscalers’ subsea cable is surging 45% to 60% per year, said SubCom Chief Executive David Coughlan. “Their underlying growth is fairly spectacular,” he said.
Data requirements for hyperscalers are not solely determined by their own content requirements, such as those for globally viewed YouTube videos and Instagram photographs. These enterprises frequently run the cloud computing platforms like Amazon Web Services and Microsoft Azure that power the worldwide operations of millions of companies.
“As the world’s hunger for content continues to increase, you need to have the infrastructure in place to be able to serve that,” said Brian Quigley, who oversees Google’s subsea and terrestrial networks.
The earliest submarine cables connected cities like London and New York along important communication corridors. The west coast of Greenland, the volcanic island of St. Helena west of Africa, the southern tip of Chile, the Pacific island states, and the 8,000-person town of Sitka, Alaska, are among the newer routes providing bandwidth far off the beaten path and still essential.
All of this is a result of subsea communications gradually changing. Whereas cables were formerly the exception, connecting a select few high-priority urban areas, they are now evolving into a mesh that spans the globe. In other words, subsea cables are starting to look like the rest of the internet despite their high costs and unusual technology.
Why subsea cables are reaching everywhere
The financial benefits are significant. According to McKinsey, submarine cable links result in higher internet speeds, reduced costs, a 3%–4% increase in employment, and a 5%–7% increase in economic activity.
The telecommunications firms that had previously installed subsea cables withdrew from the market as hyperscalers’ traffic demands increased.
“Roughly 10 years ago, a lot of the traditional telco providers started to really focus on wireless and what was happening within their last-mile networks,” said Frank Rey, who leads hyperscale network connectivity for Microsoft’s Azure cloud computing business. The wait for new cables grew longer, with the planning phase alone stretching to three to five years. The hyperscalers needed to take control.
Hyperscalers initially started off by making investments in other people’s projects, which was a logical step since that consortia of numerous allies frequently operate subsea cables. Hyperscalers now create their own in greater numbers.
A substantial cable buildout was the outcome. From 2023 to 2025, according to TeleGeography, which regularly monitors subsea cables, $10 billion will be spent on new subsea cables worldwide. Curie, Dunant, Equiano, Firmina, and Grace Hopper are just a few of the Google-owned cables that have already been constructed. Two other transpacific cables are also on the way: Topaz this year and TPU, with AT&T and other partners, in 2025.
Such cables don’t come cheap: A transatlantic cable costs about $250 million to $300 million to install, Mauldin said.
The cables are critical. If one Azure region fails, data centers in another region come online to ensure customers’ data and services keep humming. In the US and Europe, terrestrial cables shoulder most of the load, but in Southeast Asia, subsea cables dominate, Rey said.
With the hyperscalers in charge, pushing data instead of voice calls, subsea networks had to become much more reliable. It might be a minor irritation to get a busy signal or dropped call, but interruptions to computer services are much more disruptive. “If that drops, you lose your mind,” Coughlan said. “The networks we make today are dramatically better than what we made 10 years ago.”
The origin story of subsea communications
Hyperscalers initially started off by making investments in other people’s projects, which was a logical step since that consortia of numerous allies frequently operate subsea cables. Hyperscalers now create their own in greater numbers.
A substantial cable buildout was the outcome. From 2023 to 2025, according to TeleGeography, which regularly monitors subsea cables, $10 billion will be spent on new subsea cables worldwide. Curie, Dunant, Equiano, Firmina, and Grace Hopper are just a few of the Google-owned cables that have already been constructed. Two other transpacific cables are also on the way: Topaz this year and TPU, with AT&T and other partners, in 2025.
But better technology was developed thanks to investors seeking to profit from speedy communications. Increased signal transmission was made possible by higher copper purity, superior sheathing to avoid cable breaks, repeaters spaced periodically along the cable to increase signal intensity, and the use of polyethylene insulation in place of the older gutta-percha tree-derived rubber insulation.
As telegraph communications were finally superseded by telephone calls, technology advanced. A transatlantic cable put in place in 1973 could support 1,800 calls running simultaneously. The first transatlantic connection to employ glass fiber optic strands rather than copper wires was constructed by AT&T in 1988, increasing capacity to 40,000 simultaneous phone calls.
SubCom’s subsea cable factory dates back to its rope-making roots in the 1800s. “Most rope in that time was used on ships or needed to be transported by ships,” CEO Coughlan said. “A factory on a deep port, with quick access to the ocean and with winding capabilities, is what was needed to transform into the telephone cable business.”
The tech inside subsea cables
Laser light pulses are used to transport data across fiber optic links. Using different light frequencies, or colors to you and me, allows for the simultaneous transmission of more data, just as terrestrial fiber optic lines. Data is encoded into the light for transmission and decoded once it is received by network equipment on land at either end of a cable.
Although fiber optics are excellent for long-distance and fast broadband data transmission, the technology has its limitations. To increase the signal power, a large bulge in the cable known as a repeater is placed every 30 to 60 miles.
However, repeaters need electricity, which is where another aspect of the cable’s design comes into play. A copper coating outside the fiber optic strands carries electricity up to 18,000 volts. Even though power is normally available from both ends for increased reliability, that is enough to power repeaters all the way across the Pacific Ocean from just one end of the cable.
Why not keep raising the laser power, so you don’t need repeaters as often? Because boosting it too high would eventually melt the fibers, said Brian Lavallée, a senior director at networking technology giant Ciena.
His business manufactures the network hardware at either end of the subsea cables, and it uses various data encoding techniques to cram as much data as possible onto each fiber by adjusting the frequency, phase, and amplitude of light waves.
“We’ve been able to get very, very close to the Shannon limit, which is the maximum amount of information you can send down a communication medium,” Lavallée said.
How ships install subsea cables
Companies that construct cables begin by choosing a route and assessing it to avoid marine issues including nature preserves, a rugged seafloor, and existing cables. Finding a mutually accepted path and acquiring approvals can be quite challenging when several nations, enterprises, and telecommunications companies are involved.
From specialist ships, the wires themselves are progressively released. That is more complicated than just unwinding your line when flying a kite in the wind.
Subsea cables are bigger, heavier, and bulkier than fiber optic strands, which are narrower. They are transported from ship to ship or from ship to shore in metal cylinders that coil and unwind the cables. Three “tanks” on one ship can contain 5,000 tons of cable, or 1,800 miles of lightweight cable plus 600 miles of cable that has been hardened for use in crowded waters.
To ensure that the right end of the cable is at the top of the coil when installation starts, SubCom must determine the installation sequence for each cable segment. This implies that the cable must be “flipped” the other way up in storage at SubCom’s depot before being loaded onboard the ship. As it is transmitted loop by loop onto the ship, it changes direction to the proper configuration, according to SubCom’s Coughlan.
Even if that’s already challenging, revisions to the installation schedule may be required due to the weather, permits, or other issues. That can necessitate maneuvering a cable while at sea between two ships. Trying to account for elements like the ships rocking on the open sea and the cable’s weight and bending restrictions turns out to be an analog difficulty in a very digital industry.
Coughlan remarked, “We have one man in particular who is really a prodigy at this. We discovered that computer modeling never works, thus he must first be able to solve it by hand using string.
With a special plow trailed behind the ship, cables are protected with steel cable and buried in the seabed close to shore. Every time the newly attached cable crosses an existing one, the plow pushes up into the water. The cable provides less protection and is simply put on the ocean floor in deeper waters where fishing gear and anchors are not a hazard.
Fixing severed subsea cables
Although submarine cables are rather durable, TeleGeography reported that one is severed every three days or so. The main offenders, which are responsible for around 85% of cuts, are fishing gear and anchors. Frequently, ships will anchor themselves to weather storms, however the storms push the ships and cause the anchors to drag
The majority of the other cuts, such as mudslides and earthquakes, are caused by the Earth itself. Another illustration is Tonga, where a volcanic explosion cut off its only undersea cable link.
Rey from Microsoft is concerned about human-caused climate change, which is causing increasingly severe storms. Large-scale climate events are what keep him awake at night, he admitted. According to him, Hurricane Sandy in 2012 severed 11 of the 12 high-capacity cables linking the US and Europe.
The majority of cuts happen nearer to the shore, where there is more boat traffic and shallower water. Even if the wires are covered in metal armor and buried in the ocean floor there, cable cuts nevertheless happen eventually, not if. According to Google’s Quigley, more than ten cables are frequently cut simultaneously throughout the world. The worst time for outages is from October to December due of both increased fishing activity and more severe weather.
Cable operators can locate where cables have been severed, but repair ships frequently have to wait for official approval. Rey claimed that repairs take two weeks on average, but Takahiro Sumimoto, head of NTT’s maritime cable division in Japan, noted that repairs often take three to four weeks. Following the 2011 Fukushima earthquake, it took two months.
“It was too deep, and the cable was cut into pieces,” Sumimoto said.
A ship must fish up one end of the damaged cable in order to make the repair, frequently by latching on with the same type of grappling apparatus that has been in use for millennia. While the other end of the cable is being retrieved, the ship floats that end of the cable with a buoy. The ship rejoins the optical cables using thicker packages to house the splices.
Faster new subsea cable tech
There is a huge incentive to cram in more data because installing wires is so expensive. There is plenty of room for more optical fibers, but that strategy is constrained by the repeaters’ requirement for electrical power.
The new cables of today use 16 pairs of fibers, whereas the 350Gbps line NTT is developing between the US and Japan uses 20 pairs of fibers. On its transatlantic connection, NEC, another major Japanese tech company, is able to achieve 500Tbps, or a half petabit per second, rates utilizing 24 fiber pairs.
“Everywhere we looked, there was a capacity shortfall, especially after the pandemic. New wires must be built immediately, Sumimoto added. “Things are a little out of control. The capacity is immediately sold out if we build a cable.
In some cases, older cables can be upgraded with new network hardware in addition to the installation of new cables. According to Lavallée, a recent Ciena upgrade tripled the capacity of fiber optic lines without affecting anything below the surface.
Microsoft is also placing its bets on basic advancements in optical fibers. It purchased Lumenisity, a firm that was producing hollow fibers with a tiny central air tube, in December. A major factor limiting the performance of networks is the communication delay known as latency. It is 47% faster in air than in glass.
The latency of transpacific cables is around 80 milliseconds. For time-sensitive computer interactions, such as financial transactions, reducing latency is crucial. Hollow fibers for shorter-haul fiber optic links are also of interest to Microsoft since they effectively put data centers closer together for quicker backup in the event of a failure.
Additionally, fibers with more than one data transmission core will soon be available. “We can’t get much more improvement in bandwidth over a single fiber,” said TeleGeography’s Mauldin.
The company revealed that two-core fibers will be used in part of Google’s TPU cable, but that is merely the beginning. A way to subsea cable capacity of 5Pbps was announced this year by the fiber optics company OFS. 20 times as much data as the newest wires available today.
Geopolitical tensions with subsea cables
There is just one internet, but tensions can emerge when it links diametrically opposed nations, like when China restricts Google and Facebook or US businesses cut their ties to Russia’s internet. Subsea cable technology has been a source of these techno-political tensions.
Three cables that would have connected China and the US directly were effectively cut off by the US, forcing them to divert via other Asian countries. The Financial Times said that the US also sought to discredit HMN Tech, a Chinese subsea cable installation and maintenance business that separated from Huawei.
However, there are several indirect ties with many other Southeast Asian nations, and more will develop. According to TeleGeography analyst Tim Stronge in a blog post from June, “there are 17 new intra-Asian cables that are currently in the works, and many more that haven’t been announced yet.” Additionally, there are almost no boundaries when it comes to the internet routing rules that control how traffic moves throughout the world. In other words, the location of the cables isn’t particularly important to the internet.
SubCom, which provides services to the US military as well as commercial businesses like Google, has found its operations challenged by the new geopolitics.
There are many nations that “exercise their power in ways they did in the past,” according to Coughlan, and it’s not just the China-US problem. Cabotage rules are being enforced by a number of nations, including Canada and Indonesia, and they call for work to be done in their territorial seas to be done by a sovereign ship of that nation.
This is making it difficult to determine how to carry out the work and how long permissions will last, according to Coughlan. These cabotage restrictions make it more difficult to install cables. They take more time. You have to wait to receive a ship from some of these nations since they only have one.
But in the end, the financial incentives to build the cable typically win out.
When it comes to local level conflicts, such as trade wars or outright wars, local governments desire these cables, according to SubCom’s Coughlan. “This is only being constructed for that reason,”
Vulnerabilities in subsea cables
Real vulnerabilities exist in cables. The greatest hazards are anchors and fishing gear, especially in packed hallways with numerous cables. Not a human attacker, but corrosive salt water is what the wires are intended to stop.
“These cables may be broken with ease. And a malicious person may pull it off,” Coughlan added. Subsea cables, according to a 2017 think tank report by Rishi Sunak, who is now the prime minister of the UK, are “indispensable, insecure.”
Subsea cables are susceptible, according to a 2021 analysis from the Center for a New American Security, a nonpartisan think tank on national security. It employed rival “red teams” to imitate military operations by China and Russia. Chinese strikes in these simulations cut off Taiwan, Japan, Guam, and Hawaii, whereas Russian assaults struggled because to the abundance of Atlantic subsea cables.
“In CNAS wargames, Chinese and Russian red teams launched aggressive attacks on undersea cables, specifically where they ‘land’ ashore. In nearly every case, these attacks allowed red teams to disrupt and degrade US, allied, and partner communications, and contributed to confusion and distraction at the strategic level as governments were forced to respond to sudden losses of connectivity,” CNAS senior fellow Chris Dougherty said in the report.
Sunak suggested a convention to safeguard cables, NATO wargames to better appreciate their significance, and sensors on the cable to more effectively identify threats. However, the most useful guidance was straightforward: add more cables for geographic diversity and redundancy.
Making the subsea network more resilient
Given the significance and danger of subsea cables, it is not surprising that efforts are being made to improve the technology.
There is a strong drive to expand to new landing places because of this. All of the strongest transatlantic cables arrived in New York and New Jersey during Hurricane Sandy. More people are currently departing from Florida, South Carolina, Massachusetts, and Virginia.
“If you run all cables on the same path, you’re an anchor drag away from multiple cables being brought down,” Quigley said.
Operators frequently exchange capacity on each other’s cables, providing each with a backup data path in the event that their line is interrupted. They aren’t really putting all of their communication eggs in one cable.
According to In-Q-Tel’s Bowsher, “people are trying to build resilience into the system.”
Ultimately, improved branching technology that makes multistop cables affordable is helping to bring about the geographic diversity Sunak needs. The new Sea-Me-We 6 cable travels via 17 other nations before reaching Singapore from France. In addition, additional cables are being constructed to link several island states, Asia, the Americas, Europe, Africa, and the Middle East.
They are everywhere, according to Ciena’s Levallée. “These cables are really interwoven,”