Undersea cables are the Achilles' heel of the digital world. There are increasingly frequent cases of sabotage and damage to undersea cables, which carry about 95% of the world's data traffic. It has been seen that the world's telecommunications are poorly protected against deliberate actions.
Where do the main undersea cables run?
Important undersea cables include high-voltage direct current (HVDC) transmission cables, which carry electrical energy over long distances, for example to islands or to connect offshore wind turbines. They are more efficient than alternating current systems.
Telecommunication cables consist of fiber optic wires that carry about 95% of the world's data traffic, including internet and telephone calls. This is done with little signal delay. For example, calling up a website in the US from Europe takes about 60 milliseconds, the blink of an eye. There are also special cables for data centers or large network nodes, as well as more heavily shielded special cables for military communications or scientific work.
Why aren't satellites an alternative?
Only a small part of international communication is carried by satellite. This is because submarine cables can transmit much more data at a lower cost. Satellite connections are also slower and more susceptible to interference.
However, the US and the EU are investing in satellite technologies such as Starlink and the IRIS (Infrastructure for Resilience, Interconnectivity and Security by Satellite) program to create more secure, alternative communication channels.
Where are the submarine cables?
About 1.4 million kilometers of cables have been laid in about 500 directions around the world. The cables are so long that they could circle the Earth at the equator 30 times. New cables are added every year. Most cable connections are in the Atlantic Ocean between Europe and the US and in the Pacific Ocean between the US and East Asia. However, there is no complete world atlas that shows the exact location of all the cables. Platforms like submarinecablemap.com or Telegeography offer maps, but without precise location information.
The map also shows the hotspots: For example, around 90% of data traffic between Europe and Asia passes through 14 cables off the coast of Yemen. And the Houthi rebels there, in addition to disrupting shipping traffic, used a hijacked cargo ship in 2024 to attack three undersea data cables.
Who lays the undersea cables?
Until recently, the market was dominated by telecommunications service providers such as AT&T and China Telecom. Today, major technology companies such as Google, Microsoft, Meta and Amazon are investing heavily in undersea cables.
Google currently owns six active undersea cables and plans to build more. Meta has a stake in 16 existing cables and is planning its own global cable network. The presence of almost 1.5 billion people on the African continent is a particularly interesting target group for the Facebook and Instagram group.
Construction of submarine cables
Modern submarine cables consist of several layers. The inner layer is made of optical fibers that use light pulses to transmit digital information. A protective layer of steel wire (armor), polyethylene and waterproof materials is placed on top of them. They protect against the extreme pressures and conditions of the deep sea and guarantee a service life of about 25 years.
How are submarine cables laid?
Geologists and engineers determine the best place to lay the cable, taking into account obstacles such as unevenness and dips in the seabed, ocean currents, fishing grounds and shipping routes. In the North Sea and the Baltic Sea, around 1.6 million tonnes of discarded munitions from past wars also pose a major challenge.
Where there is a risk to the cable - on the coast or in shallow water - a trench up to 3 metres deep is usually dug, in which the cable is laid. A special plough is used for this purpose. The trenches are not backfilled, as the sea currents do the job themselves.
In deeper waters, where the risk of damage is lower, the cable is often laid directly on the seabed by special cable-laying vessels. Particularly large submarine cables with a diameter of over 20 cm can weigh between 40 and 70 kg per linear metre – because of their protective sheath.
The distance between the laying vessel and the point where the cable touches the seabed can be up to 8 kilometers. It is important to keep the cable taut during the laying process. Otherwise, loops can form. However, if it is too taut, the cable can also break.
Damage to submarine cables
Most damage is caused by trawls or anchors. Deliberate sabotage as part of hybrid warfare has been known since the Cold War. As early as 1959, the Americans accused the Russians of deliberately damaging an underwater cable with fishing nets.
Espionage is also a serious problem, especially when the cables belong to systemic rivals such as China or the United States, as underwater cables can be tapped or intercepted.
Repair of underwater cables
Repair is complicated by the extreme pressure conditions and unpredictable weather conditions. Specialized equipment can measure the loss of signal and determine the location of the damaged section. With modern fiber optic cables, damage can be determined with an accuracy of up to 50 meters.
Depending on the damage and depth, divers can repair the cable using so-called dry chambers. If this is not possible, a cable repair ship carefully raises it to the surface, where technicians on board replace the damaged sections of the cable with new ones. This takes a lot of time, as all connections must function flawlessly even under adverse conditions. After extensive testing, the cable is carefully lowered back into the water and, if necessary, reburied. However, there are only a few ships in the world that can carry out such repairs. Sometimes they need weeks or even months to repair a broken cable.
Protective measures for underwater cables
Underwater cables are well protected from natural threats, but they are often insufficiently protected from deliberate damage by hostile states, secret services or terrorists. The use of underwater drones and acoustic sensor systems can help to detect potential sabotage early.
At the same time, additional cable connections are being set up as backup systems so that data can be transmitted even if one cable fails. Recently, the countries affected have been developing coordinated protection strategies so that they can act quickly and jointly in the event of an attack. This also requires close cooperation between countries, submarine cable operators and international organizations.
New legal frameworks are also needed at national and international level. This is because there are currently no specific provisions in international law to protect submarine cables in the event of conflict.
Author: Alexander Freund