The JRC explains: Subsea cables: how vulnerable are they and can we protect them? JRC explains | 8 August 2025 | Joint Research CentreEven though subsea cables have been placed in our seas since the 19th century, they have gained attention in recent years due to a series of incidents in the Baltic Sea. The incidents have exposed the vulnerability of these networks to damage and disruption. Why are subsea cables important? Subsea cables, carrying electricity or data, nowadays criss-cross Earth’s seas and oceans for a total length exceeding 1.3 million km - more than 32 times Earth’s circumference at the equator.There are now over 400 active cables worldwide. They carry as much as 99% of inter-continental internet traffic and bring offshore renewable energy to shore, strengthening the security of supply. What do they look like? Typical submarine power cables can have a diameter of 7 cm to 21 cm, with a cross section of a three-core power cable. They are armoured with steel wire and have an extra protection layer known as serving or oversheath. Telecommunication networks use thinner (up to 4-5 cm in diameter), lightweight cables, consisting of optical fibres covered by layers of polyethylene, copper and possible protective steel wire armour layers. In the deep sea, where bottom trawling fishing is not carried out – over 2000 m of depth – subsea cables are directly laid on the seafloor. In more shallow waters, they are buried for additional protection. In some cases, the cables can also be freely suspended.The cost? Installing a submarine power cable costs on average between €1-2 million per km, while the costs for subsea telecommunication cables range from around €25,000 to €45,000 per km. What are the risks? Worldwide, there are about 150-200 accidental and unintentional subsea cable damages every year. In most cases, cable damage is caused by human activity, the leading cause being accidental damage by fishing vessels. While bottom trawling can cause damage and entanglement of cables up to depths of 2000m, damage due to anchors is more typically observed in shallow waters.Other “culprits” include geological events – such as volcano eruptions or earthquakes –abrasion and fatigue, caused by currents or sand waves, or issues related to an ageing infrastructure. But over recent years, a number of incidents have raised concerns about possible malicious acts by foreign actors. Media has widely reported on incidents caused by potential sabotage, although some of those may have been accidental damage. Suspicions have been raised against state-sponsored actors for weaponising fishing or oil vessels, and causing intentional damage to subsea infrastructure using anchors, fishing or trawler gear, and dredging devices.Once damaged, repair is carried out either by cable repair vessels or submersibles for cables that lie in shallower water. Such interventions are costly and, in the case of power cables, cause additional losses of power production and transmission during the repair time, which may last several weeks or months. Moreover, the lack of sufficient maintenance and repair vessels slows down recovery. How to protect them? Physical protection, such as burial techniques including rock placement and mattress coverings, can effectively prevent damage to subsea cables. But they may not be sufficient to protect against intentional damage or sabotage. Therefore, burial techniques should be combined with other protection measures, such as monitoring and surveillance, to detect and respond to potential threats. Deterrence and prevention include the use of monitoring systems such as radars, vessel monitoring systems, or automatic identification systems – i.e. short-range coastal tracking systems for ships – as well as patrolling by air, satellite use, sea and land. Recent examples include the NATO flotilla in the Baltic Sea, assembled in early 2025. Additionally, the establishment of designated offshore sectors or corridors, in which fishing and anchoring restrictions apply, can be instrumental to reduce accidental damage and identify malicious actors.Read more on risks and protection of subsea cable networksBurying subsea cables into the seabed is the most common way of protecting them in shallow sea. A subsea mechanical trencher is used where the seabed consists of very hard clay, rock, or mixed soils with gravel/stones.Source: 2010 Marine Technology Society - (CC BY-NC-ND 4.0) What is the EU doing? The EU's security and economic stability depend on the resilience of these networks, making their protection a top policy priority, reflected in the EU Action Plan on Cable Security. Published in February 2025, the plan introduces a range of measures to bolster the resilience of this critical infrastructure, addressing prevention, detection, response, recovery, and deterrence.Other pieces of EU legislation, strategies and financial instruments also contribute to the resilience and protection of subsea cables, such as the following:Directive on measures for high common level of cybersecurity, Directive on Critical Entities Resilience (CER),Revised EU Maritime security strategy, Trans-European Networks for Energy (TEN-E) guidelines,EU Strategy to harness the potential of offshore renewable energy for a climate neutral future,Connecting Europe Facility (CEF) funding for the digital and energy sectors.
Typical submarine power cables can have a diameter of 7 cm to 21 cm, with a cross section of a three-core power cable. They are armoured with steel wire and have an extra protection layer known as serving or oversheath. Telecommunication networks use thinner (up to 4-5 cm in diameter), lightweight cables, consisting of optical fibres covered by layers of polyethylene, copper and possible protective steel wire armour layers. In the deep sea, where bottom trawling fishing is not carried out – over 2000 m of depth – subsea cables are directly laid on the seafloor. In more shallow waters, they are buried for additional protection. In some cases, the cables can also be freely suspended.The cost? Installing a submarine power cable costs on average between €1-2 million per km, while the costs for subsea telecommunication cables range from around €25,000 to €45,000 per km.
Physical protection, such as burial techniques including rock placement and mattress coverings, can effectively prevent damage to subsea cables. But they may not be sufficient to protect against intentional damage or sabotage. Therefore, burial techniques should be combined with other protection measures, such as monitoring and surveillance, to detect and respond to potential threats. Deterrence and prevention include the use of monitoring systems such as radars, vessel monitoring systems, or automatic identification systems – i.e. short-range coastal tracking systems for ships – as well as patrolling by air, satellite use, sea and land. Recent examples include the NATO flotilla in the Baltic Sea, assembled in early 2025. Additionally, the establishment of designated offshore sectors or corridors, in which fishing and anchoring restrictions apply, can be instrumental to reduce accidental damage and identify malicious actors.Read more on risks and protection of subsea cable networksBurying subsea cables into the seabed is the most common way of protecting them in shallow sea. A subsea mechanical trencher is used where the seabed consists of very hard clay, rock, or mixed soils with gravel/stones.Source: 2010 Marine Technology Society - (CC BY-NC-ND 4.0)
