How Submarine Cables Power Our Lives, Shape Politics, and Face Growing Threats
Over 99% of international data traffic travels through fibre optic cables laid on the seabed known as undersea communications cables, or submarine cables. This hidden but essential infrastructure has a history that spans 200 years and involves technological advancements as well as political conflicts. Let’s analyse how modern undersea cables were developed, how they are constructed and placed today, analyse their role in global politics and their future outlook.
The Birth of Undersea Cables
The story of undersea cables begins in the 1840s, after the telegraph had been invented and ideas for a transatlantic submarine line for communication between Europe and America began to take root. After some experiments using different types of insulators to protect the telegraph wire in water, the first successful submarine communications cables were laid in the 1850s. 1858 saw the establishment of the first transatlantic cable, although it was only operational for a month. More successful attempts were made in 1865 and 1866.
After that, it only took a few more years for all the world’s continents (except Antarctica) to be connected, after a cable was laid between the island of Java and Darwin, Australia in 1871. After the telegraph, subsequent generations of cables carried telephone traffic and then data communications traffic. The early cables used copper wires in their cores.
The first transatlantic telephone cable was laid in 1956. In the 1980s, fibre-optic cables were developed, which are the cables we use today to carry digital data including telephone, Internet and private data traffic. They are the most efficient and reliable means we have of transmitting data across great distances. The undersea telegraph cables from almost 200 years ago ended up revolutionising communication and paving the way for the modern Internet.
How Undersea Cables Are Built – Not Your Phone Charger Cable
Modern undersea cables use fiber-optic technology, which comprises thin optical fibers made of glass or plastic and operate based on the principles of light transmission – data is converted into light pulses, which bounce off the inner walls of the fiber, reflecting back and forth until they reach the other end. It’s a very efficient way to transmit data.
In order to withstand undersea conditions, undersea cables have multiple layers for protection and durability. The optical fiber makes up the core of the cable, which is then covered by cladding, a protective layer to ensure that none of the light leaves the fiber and minimise data loss. Next, layers of plastic and metal provide structural support and protect the cables from water or other physical damage from the environment.
Laying the cables on the seabed requires a lot of prep. First the route of the cable needs to be determined and thorough marine and geological surveys are performed to ensure that the route is secure. Once a safe and efficient route is found, it also needs to be cleared of any obstructions. Then the cable is loaded onto the cable laying vessel and transited to the site, where it is laid on the seabed and, in shallower waters where it needs more protection, buried under the seabed.
Specialised ships are also needed for cable maintenance. If cables are damaged, for example as a result of a natural disaster, these ships will locate and repair the damage, which could take up to several weeks.
The process of setting the undersea cables essential for modern communication is fraught with challenges, mostly due to their submarine environment, and the time from initial planning to the finished laying of a cable may take multiple years.
The Global Network of Cables
Undersea cables now connect all the continents except Antarctica, allowing information to be transmitted quickly throughout the whole world (although some more remote places still rely on satellites). Over 99% of the world’s data goes through undersea cables. As of early 2025, there are about 600 active and planned undersea cables globally.
The world’s largest undersea cable was the so-called SEA-ME-WE3 cable connecting South-East Asia, the Middle East and Western Europe, with 39,000 kilometres of length. However, the cable was declared end-of-life in December 2024 and is no longer in use. Meta is planning to build the next largest cable connecting the US, India, South Africa and South America, which would be 50,000 kilometres long. That’s more than the Earth’s circumference, which is 40,075 km. However, this project will take several years to complete and is currently only in its planning phase.
The most important routes of undersea cables are the transatlantic route from Europe to North America, the transpacific route from North America to East Asia, and the aforementioned SEA-ME-WE route reaching from South-East Asia to Western Europe through the Middle East. There are important hubs in coastal areas on every continent, some of which include Singapore, Egypt, Marseille, Tokyo, Fortaleza and Oman. In Europe, underseacables connect Scandinavia with the Baltic countries, Iceland with Europe, North Africa with Italy, Spain and France, the Balkans with Italy. The Caucasus is connected to Bulgaria and the rest of Europe through cables under the Black Sea.
Cables as Geopolitical Tools
Undersea cables have been used as a political tool since the very start of their history. In World War I, Britain’s first action after declaring war on Germany was to cut the five cables linking Germany with France, Spain and the Azores, and through them, with North America. This meant Germany could only communicate by wireless, which was easier for Britain to intercept.
As recently as November 2024, two undersea cables in the Baltic Sea were disrupted. While no clear culprit has been identified, many have been pointing fingers at China (who had a cargo ship in the vicinity during the incidents) and Russia (who may have been influencing China). The Chinese cargo ship is under investigation by European authorities. In January 2025, a similar incident happened in the Baltic Sea, in relation to which a Russian-crewed ship is under investigation. With multiple incidents happening in close succession, many consider it unlikely to be a coincidence.
Whether or not this specific disruption was intentional, the potential vulnerability during a time of global tension cannot be ignored. With most of our global communication relying on undersea cables, their protection is important.
Historically, the construction and laying of undersea cables has been dominated by three companies – SubCom from the USA, NEC Corporation from Japan and Alcatel Submarine Networks from France. Due to the high costs and risks associated with the projects, cables are usually owned by a consortium of parties, which helps to make them politically more neutral – it is in everyone’s interests to keep the cables running smoothly.
Things changed in 2008, when Chinese HMN Technologies entered the market, and by 2020, they had built or repaired almost 25% of the world’s undersea cables. The USA particularly wants to keep China from having too much control over global communication routes, thus pressuring other companies to unite to keep China out of the market, sparking a potential tech-war.
Others think the geopolitical tech-war is based on fearmongering more than actual threats. An EU report from 2022 suggests that any large-scale purposeful damage inflicted via undersea cables is highly unlikely. Rather, the pressure to keep China out of the market, thus essentially creating two global blocs with different levels of access to submarine communications infrastructure, could deepen global inequalities. International cooperation in keeping communication lines open is crucial. Yet being prepared for conflict is also a very smart thing to do, as many experts also thought the Russian invasion into Ukraine to be unlikely.
The Future of Undersea Cables
While satellites have been creating more buzz lately (Starlink and so on), there is no doubt that undersea fiber optics cables are still the best method for transcontinental data transmission. Satellites are cheap and effective options for remote areas that don’t have access to undersea cable infrastructure, but for the vast majority of the population, undersea cables will remain the primary method of staying in touch with the world for the foreseeable future.
Undersea cables are invisible but critical infrastructure in our globalised, connected modern world. Next time you view a website hosted by a server situated across the ocean, know that it’s travelling to you through glass fibers under the sea. We need to appreciate and protect these essential cables and keep geopolitical conflicts from (literally and figuratively) cutting our access to the world. And when a conflict is unavoidable, taking a firm stance against an aggressor is usually the best deterrent.
As global tensions rise and the world becomes increasingly multipolar and unstable, undersea cables—critical to our digital infrastructure—are likely to face more frequent and sophisticated attacks from various actors. On one hand there are the usual suspects, dictatorships eager to disrupt the system, but potentially also criminal organisations or pirates looking for ransom money. Overlooking this emerging threat would not only be naïve but also perilous, given the potential for significant disruptions to communication, finance, and national security.
Sources:
1. Diagram: https://en.wikipedia.org/wiki/Submarine_communications_cable#/media/File:Submarine_cable_cross-section_3D_plain.svg
2. Map: https://commons.wikimedia.org/wiki/File:Submarine_cable_map_umap.png
