How Undersea Internet Cables Work and Why They Matter
Learn how undersea internet cables work, how data travels across oceans, why cables break, how repairs are done, and why they matter to global internet access.
Raja Awais Ali
8/21/20264 min read
How Undersea Internet Cables Work and Why They Matter
When people think about the internet, they usually think of mobile towers, Wi-Fi routers, data centers and satellites. But a major part of the global internet depends on a network that remains hidden beneath the world's oceans: undersea internet cables. These fiber optic cables connect continents and allow enormous amounts of data to move between countries every second. According to the International Telecommunication Union (ITU), submarine cables carry more than 99 percent of international data traffic, making them one of the most important parts of the global digital infrastructure. The world's submarine cable network includes more than 500 cable systems and stretches for more than 1.4 million kilometers.
Undersea internet cables work through fiber optic technology. Inside each cable are extremely thin strands of glass that transmit information as pulses of light. Data from websites, cloud services, video calls, online banking systems and other digital platforms can travel through these cables between countries and continents. The technology allows large volumes of information to move across oceans at very high speeds while maintaining reliable international connections.
A submarine cable is not simply a thin fiber placed on the seabed. The optical fibers are surrounded by several protective layers designed to protect them from pressure and physical damage. Cables installed close to shore usually receive additional protection because coastal waters are exposed to fishing activity, ship traffic and anchors. In deeper parts of the ocean, cables can often rest directly on the seabed because there is less human activity around them. The design depends on the location, water depth and level of risk along the route.
The global submarine cable network has continued to expand as demand for international data capacity increases. ITU reported that bandwidth demand has been growing by about 22 percent each year since 2021. Cloud computing, artificial intelligence, video streaming, online services and international businesses are all increasing the amount of data that needs to move between different regions. Global investment in submarine cable infrastructure also increased from about $0.8 billion in 2015 to $9.7 billion in 2025, showing how important these networks have become to the digital economy.
The importance of undersea cables becomes clearer when one considers how international internet services actually work. A user in one country may access a website, cloud platform or server located thousands of kilometers away. The data can pass through local networks before reaching a submarine cable landing station, where it enters an undersea cable and travels across the ocean. At another landing station, the data returns to a terrestrial network and continues toward its destination. The same process works in reverse when information is sent back to the user.
The world does not depend on a single submarine cable. Hundreds of cable systems create different routes between continents, allowing networks to redirect traffic when a particular cable is unavailable. This redundancy is important because a damaged cable does not normally mean that an entire country's internet will stop. However, some countries and islands have fewer international connections than major digital hubs. If an important cable serving such a region is damaged, users can experience slower speeds, higher latency or interruptions to certain online services.
Submarine cables can be damaged for several reasons. Human activity is one of the biggest risks, particularly in shallow coastal waters. Fishing equipment and ship anchors can come into contact with cables and cause faults. Natural events can also damage the network, including earthquakes, underwater landslides and other changes to the seabed. ITU estimates that around 150 to 200 submarine cable faults occur globally each year, while about 86 percent of faults are linked to human activity.
Repairing a damaged cable is a specialized operation and cannot usually be completed immediately. Engineers first identify the approximate location of the fault using network measurements. A specialized cable-repair vessel is then sent to the area. The crew locates the cable, brings the damaged section to the surface, removes or repairs the faulty part and reconnects the cable. After testing the repaired section, the cable is placed back on the seabed. Weather, sea conditions, permits, customs procedures and the availability of repair vessels can all affect how quickly the work is completed. In some cases, repairs can take weeks or longer.
The location of a cable fault can also determine how serious the disruption becomes. A region connected to several independent cable routes may be able to move most traffic to alternative systems. A region with only a few international connections has less flexibility. This is why countries and network operators are increasingly focusing on route diversity, additional landing stations and faster repair capabilities rather than relying on a small number of connections.
The growing importance of submarine cables has also made their resilience an international issue. Governments, telecommunications companies and technology firms are investing in new cable systems and working on ways to reduce the effect of cable failures. In 2024, the International Telecommunication Union and the International Cable Protection Committee established the International Advisory Body on Submarine Cable Resilience. Its work focuses on improving cooperation, monitoring risks and strengthening the ability of countries and companies to respond when important cables are damaged.
The expansion of artificial intelligence and cloud computing is likely to increase the need for international data capacity. New data centers, AI services, streaming platforms and global online businesses require reliable connections between different parts of the world. ITU data shows that almost 200,000 kilometers of new submarine cables were installed in 2024, while investment in the sector reached $9.7 billion in 2025. These figures show that the global undersea cable network is continuing to grow alongside the wider digital economy.
Despite the growing role of satellites and wireless technologies, undersea fiber optic cables remain the main physical connection for international internet traffic. They provide the capacity needed to move large amounts of data between continents and support services that people and businesses use every day. Most users never see these cables or think about them, but their internet connection can depend on infrastructure lying thousands of meters below the ocean surface.
The future of the global internet will therefore depend not only on faster networks on land but also on a stronger and more reliable international cable system beneath the oceans. More cable routes, greater capacity, better protection and faster repairs can reduce the impact of individual failures. As global data use continues to rise, the thin fiber optic cables crossing the world's oceans will remain a critical part of how countries, companies and billions of people stay connected.
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