Subsea and seabed warfare (SSW) refers to undersea warfare targeting critical infrastructure on the seabed, posing a growing threat to national security and economic stability. The seabed hosts vital infrastructure such as undersea cables and pipelines, which are increasingly at risk due to sabotage and accidents. Authoritarian states and non-state actors are becoming more willing to target these installations, with potential consequences for communications, energy supplies and financial systems. The biggest threats to subsea cables come from human activities, with anchors and fishing being the primary causes of damage. European nations and Taiwan have been particularly vulnerable to SSW, while Russia and China have developed capabilities to exploit these vulnerabilities.

An image of the ocean

To address these challenges, a variety of protective and response measures are required, including better maritime domain awareness, enhanced military preparedness, improved information sharing, strengthened operational coordination, enhanced physical cable security, cybersecurity measures, international legal efforts, and developing internationally recognised and formalised protections. Collaborative efforts between governments, military and industry are essential to ensure the security and resilience of subsea critical infrastructure.

Key takeaways

  • Warfare targeting underwater or subsea critical infrastructure is variously described as seabed warfare, or subsea and seabed warfare (SSW). It broadly refers to undersea warfare in which the seabed is the focus. Commentators note that undersea warfare is not new. What is new is the growing threat to critical infrastructure on the seabed.

  • There is a growing recognition that seabed infrastructure may be targeted in the event of conflict between major powers.

  • Undersea cables and pipelines are vulnerable and are now at risk with the sabotage of undersea installations occurring at an accelerating rate. This creates economic risks as well as disruption to essential services and critical systems. 

  • Sabotage of undersea and seabed installations is being undertaken more brazenly. Authoritarian states and rogue non-state actors are more willing to target vital infrastructure. 

  • The biggest threats to subsea cables come from human activities. As most incidents are the result of accidents, it is difficult to attribute blame and formulate appropriate responses.  

  • European nations and Taiwan have proven particularly vulnerable to SSW, but the Red Sea has also demonstrated the vulnerability of subsea and seabed infrastructure and the impacts of damage. 

  • Russia is simultaneously less vulnerable to targeting and disruption of subsea cable infrastructure and potentially more willing to exploit these vulnerabilities in other nations. China has invested research and development into technology to damage undersea cables.

  • A variety of protective and response measures are required, including:

    •  better maritime domain awareness

    • enhanced military preparedness and resilience

    • improved information sharing and best practices between civilian authorities, the military and industry

    • strengthened operational coordination efforts

    • enhanced physical cable security

    • cybersecurity measures

    • international legal efforts

    • developing internationally recognised and formalised protections. 

Subsea and Seabed Warfare 

In ‘Seabed warfare: Protecting the UK’s undersea infrastructure’, Louisa Brooke-Holland defines seabed warfare as broadly referring to undersea warfare in which the seabed is the focus. Brooke-Holland adds that undersea warfare is not new—submarines have long played a vital role in naval operations—but ‘what is new, or at least becoming more widely discussed in public, is the growing threat to critical infrastructure on the seabed and the resulting risk to national security’. The United Kingdom (UK) Ministry of Defence says the growing use of the seabed has ‘increased opportunities for adversaries to threaten Western subsea critical national infrastructure’, while a NATO Parliamentary Assembly committee draft reported that seabed warfare is ‘no longer a distant concept’ but ‘represents an immediate and legitimate threat’. 

Brooke-Holland referenced several official defence reports dating from 2021 of the threat posed by Russia which is developing ‘deep sea capabilities which can threaten undersea cables’, has ‘phenomenally increased submarine and underwater activity’ over the last 20 years, is ‘very active’ in everything related to underwater combat, and is ‘actively mapping’ gas pipelines and internet cables. In response, Brooke-Holland cites the UK Ministry of Defence’s accelerated procurement of a new ship, RFA Proteus, specifically to detect threats to the seabed and cables. 

Elisabeth Braw in ‘Russia’s Cable-Cutting Could Threaten Europe’s Whole Energy Supply, stresses that undersea cables and pipelines are now at risk with the sabotage of undersea installations occurring at an accelerating rate. Braw highlights that those orchestrating suspected cable sabotage incidents are becoming decidedly brazen, with consequences for communications and crucial energy supplies. With its transition to green energy, Norway’s energy production now depends on electricity cables—and in turn, so does the rest of Europe. In 2022, Norway became the biggest supplier of natural gas to the European Union (EU). In the first quarter of 2023, 46 per cent of the EU’s pipeline natural gas imports came from Norway. Its exports of crude oil have also increased since February 2022. Norway is also the UK’s largest supplier of gas and crude. Braw observes that with the slicing of a few cables, Russia, potentially with the assistance of China, could disrupt a continent.

Cynthia Mehboob concurs with Braw’s conclusion on the growing risk and brazenness in ‘NATO’s best-laid subsea cable security plans’. Mehboob says that incidents of sabotage like that of C-Lion1 underscore the growing willingness of authoritarian states and rogue non-state actors to target vital infrastructure. This creates economic risk but also the risk of disruption of essential services and critical systems.  Mehboob argues that as the danger to NATO nations escalates from provocation to existential threat, the West’s response must be more robust and swift. Countries must work together to create enforceable international agreements that hold perpetrators accountable and impose meaningful consequences. A stronger strategy to protect critical digital networks is required as is a direct warning to malicious actors. For Mehboob, western governments must also take immediate action to strengthen the protection of physical infrastructure and establish rapid-response protocols for real-time attacks. 

In ‘International law doesn’t adequately protect undersea cables. That must change’, Amy Paik and Jennifer Counter likewise advocate for an effective regime to hold the perpetrators of a physical attack accountable. Currently, there is no such way to do so. Paik and Counter contend that while the United States (US) and its allies and partners have come to understand how important it is to secure the world’s undersea cables, there has not yet been enough effort to incorporate all countries in a protection pact. With the prospect that lives of citizens in countries across the globe could be severely impacted, intergovernmental organisations such as the United Nations (UN) must take undersea cable security seriously, including by forming internationally recognised and formalised protections.

Sophia Besch and Erik Brown in ‘Securing Europe’s Subsea Data Cables’, reiterates Europe’s dependency on subsea infrastructure and its ‘glaring vulnerability’ to sabotage. They note that more subsea data cables connect to Europe than to any other continent around the world, but it was not until 2022 and the invasion of Ukraine that European policymakers began to pay significant attention to the security of these cables. For Besch and Brown, the involvement of a Hong Kong–flagged vessel in the October 2023 Balticconnector incident also sparked awareness among Europeans of China’s potential interest in physically damaging undersea infrastructure in and near Europe. In addition to damage, intentional or otherwise, Besch and Brown underscore authorities’ fear of a range of threats: backdoors could be installed during the cable manufacturing or repair process; cable-landing stations could become targets to cyberattacks; and rapid advances in subsea technology might allow adversaries to tap cables at sea.

Their paper briefly maps the economic significance, strategic vulnerabilities and key players of Europe’s undersea cable infrastructure. It then outlines the recent evolution of the European debate on the physical and economic security and cybersecurity of subsea cables, sketching the European perspective on the activities of Russia, China and the US in this field. European countries’ steps—taken through NATO, the EU and other multilateral groupings—to protect their subsea cable networks and increase their global competitiveness are also described. Finally, it identifies shortcomings of current approaches and offers a list of policy recommendations, with a view to improving the physical security, cybersecurity and resilience of European undersea data cables.

Rajeswari Pillai Rajagopalan in ‘Undersea Cables are Increasingly Critical and Vulnerable, illustrates that the threat is not confined to European waters, describing an alleged attack by the Houthis which tampered with many communication cable lines, including Asia-Africa-Europe 1, the Europe India Gateway, Seacom and TGN (Tata Global Network)-Gulf, and Hong Kong-based HGC Global Communications. The cuts impacted 25 per cent of the communications passing through Red Sea from Asia to Europe. Rajagopalan reminds us that while the Red Sea has long been considered a maritime shipping choke point, it is also ‘an internet and telecommunications bottleneck,’ according to experts at the Center for International and Strategic Studies (CSIS). Around 90 per cent of communications between Europe and Asia, as well as 17 per cent of global internet traffic, pass through cables under the narrow Bab al-Mandab Strait, making it a major chokepoint for the communication sector. 

Sean Monaghan, Michael Darrah, Eskil Jakobsen and Otto Svendsen in ‘Red Sea Cable Damage Reveals Soft Underbelly of Global Economy’, also reflect on this Red Sea incident, noting that Houthi rebels were indirectly culpable as the cables were cut by the anchor of the sinking Rubymar, a UK-owned commercial vessel that sunk after being hit by a Houthi missile. The authors recognise that there are no easy solutions for securing undersea infrastructure and that deterring grey zone aggression is difficult but not impossible. However, they contend that international governments and companies can act in two important areas: boosting resilience and enhancing maritime domain awareness. Both efforts would be furthered by improving public-private coordination, especially given the security and financial risks from vulnerable undersea infrastructure.

In ‘Cable Risk and Resilience in the Age of Uncrewed Undersea Vehicles (UUVs)’, Ash Rossiter points out there is increasing acknowledgement by scholars and government officials worldwide of the risks associated with near total global economic reliance on the undersea telecommunication cable network. Rossiter considers that the disruptive incidents in late 2024 affecting seabed infrastructure—including cables—have served only to highlight the network’s vulnerability. He examines how fast-paced technological developments in UUVs will affect the security of this critical infrastructure, including ‘what advantages this frontier technology offers to those seeking to harm the cable network, and, from the opposite perspective, for those concerned about protecting it’. 

Rossiter states that rapidly maturing technology in uncrewed undersea vehicles (UUVs) is transforming the ability to be present and operate on or at the seabed. There is a growing fear that seabed infrastructure will be targeted as conflict between major powers intensifies. Rossiter indicates there is now a common assumption that if war breaks out, cables will be openly targeted. A further layer of complexity to this security challenge addressed in the paper is the growing capabilities and reach of non-stated violent actors. Groups such as the Houthis now have tools that until recently were the preserve of states.

Alexander Lott in ‘The Baltic Sea Cable-Cuts and Ship Interdiction: The C-Lion1 Incident’ reinforces Rossiter’s remarks on the targeting of seabed infrastructure as a likely facet of modern war. Lott illustrates this by reference to the C-Lion1 incident, where on the same day (17 November 2024) that the restrictions on Ukraine’s use of long-range NATO missiles to attack Russia were lifted, a submarine telecommunications cable connecting Sweden and Lithuania was cut. The next day, the C-Lion1 submarine telecommunications cable linking Finland and Germany was also cut. Both cable cuts occurred in Sweden’s exclusive economic zone and were assessed as sabotage. Swedish and Finnish authorities launched a criminal investigation into the C-Lion1 incident focusing on the Chinese bulk carrier Yi Peng 3 that had a Russian captain. 

Lott states that submarine cables are difficult to protect against intentional cutting, and lists instances where the submarine cables of Norway, the UK, France and Taiwan have repeatedly been cut in recent years, likely by foreign ships in their maritime area, leading to disruptions to internet and banking services. These instances and the Nord Stream explosions of September 2022, and the Baltic connector incident of October 2023, underscore the vulnerability of Western states to intentional damage caused to their critical offshore infrastructure. These maritime nations are much more dependent on maritime connections than their land-based rivals China, Russia and Iran. Lott reflects that the dragging of an anchor demonstrates that primitive means can be effective against some infrastructure, while other incidents demonstrate that sometimes more specialised equipment is required.

In ‘Safeguarding Subsea Cables: Protecting Cyber Infrastructure amid Great Power Competition’, Daniel Runde, Erin Murphy and Thomas Bryja also emphasise that subsea fibre-optic cables, now carrying more than 95 per cent of international data, are becoming a highly consequential theatre of great power competition between the US, China and other stated actors such as Russia. The authors draw attention to the scale and exposure of undersea infrastructure, which make it an easy target for saboteurs operating in the grey zone of ‘deniable attacks short of war.’ For example, in 2023 Taiwanese authorities accused two Chinese vessels of cutting the only two submarine cables that supply internet to Taiwan’s Matsu Islands, plunging 14,000 residents into digital isolation for six weeks. Taiwan pointed to a remarkable frequency of Chinese vessels causing cable disruptions—27 times since 2018—and accused Beijing of harassing Taiwan through ‘grey-zone aggression.’ 

Dragonfly Intelligence in ‘Taiwan: Assessment of subsea cable sabotage, assessed in January 2025 that China is likely to step up these efforts to interfere with Taiwan-linked cable infrastructure in coming years; noting that three occasions of sabotage have been attributed to China in the 12 months prior to 4 January 2025, often in areas of busy shipping lanes. Dragonfly also assess that Taiwan has limited options to prevent further such incidents, but note enhanced monitoring efforts.

Runde, Murphy and Bryja flag a further vulnerability. While a trusted supplier may install subsea cables, they can be maintained by a repairer from a high-risk vendor, some of whom are Chinese. The overreliance on Chinese repair ships due to limited alternatives in the marketplace is another vulnerability if, during a time of military conflict, the Chinese government prohibits access to its repair ships and subsea cables are left damaged without timely repair. 

Turning to Russia, Runde, Murphy and Bryja highlight that Russia relies significantly less on subsea cables than either the US or China due to its position as a continental power with internet connectivity to Europe and Central Asia and less focus on international trade. This makes Russia less vulnerable to disruptions in subsea cable infrastructure and potentially more willing to exploit these vulnerabilities in other nations. Recently, Russian naval and intelligence assets have been observed loitering near undersea cable routes, equipped with submersibles capable of cutting or tapping into these cables, signalling a clear intent to exploit these vulnerabilities in a potential conflict scenario.

Many of Runde, Murphy and Bryja points are reiterated by Zelie Petit in ‘Beneath NATO’s Radars: Unaddressed Threats to Subsea Cables’. Petit described NATO’s implementation of a series of significant measures to strengthen its ability to detect, prevent and respond to threats, following the attacks on the Nord Stream pipelines in September 2022. The alliance’s first efforts to boost subsea cable security were in cooperation with the EU through the creation of the EU-NATO Task Force on Resilience of Critical Infrastructure in January 2023 to enhance preparedness and resilience. Then in February 2023, Secretary General Stoltenberg announced the creation of the Critical Undersea Infrastructure Coordination Cell (CUI-CC) to identify vulnerabilities and improve information sharing and best practices between civilian authorities, the military and the industry. NATO then furthered its efforts by announcing the creation of the Maritime Center for the Security of Critical Underwater Infrastructure (MCSCUI) within NATO’s Allied Maritime Command at the July 2023 NATO Summit in Vilnius. 

The MCSCUI’s primary goal is to act as an operational hub to coordinate efforts and enhance effective decision making. In October 2023 NATO, in collaboration with Sweden, launched the Digital Ocean Initiative to facilitate technology integration to strengthen seabed to space situational awareness. Petit assesses that these NATO efforts, while progressive steps which have positively contributed to enhancing physical cable security, still fail to address the full range of threats. For Petit, the approach of NATO has been mainly focused on Russian threats in the Baltic Sea, but needs to be broadened to a more complete approach to defend the entire infrastructure. 

Minna Ålander in ‘Death by a Thousand Paper Cuts: Lessons from the Nordic-Baltic Region on Countering Russian Gray Zone Aggression’ provides a comprehensive and astute analysis of Russian grey zone tactics in their entirety, including but not limited to attacks on critical subsea infrastructure – ‘multidimensionality’ as Ålander terms it. Attribution and response measures are two challenges, and Ålander calls for a collectively coordinated multilateral response and proposes a Nordic-Baltic Blueprint for More and Better EU-NATO Cooperation as the way forward.

Didi Kirsten Tatlow in ‘Exclusive—Chinese Patents Reveal Aim to Cut Undersea Cables’, has also revealed Chinese-language patent applications of 2020 demonstrate an interest in cutting cables and show that engineers in China have pursued inventions to sever undersea cables quickly and cheaply. The 2020 effort built on a 2009 patent application for an anchor-shaped ‘ocean towing type cutting device’ by marine engineers at the South China Sea branch of the Stated Oceanic Administration of China. The reason given for needing such a device was the existence of illegal cables off China that needed to be destroyed. Tatlow quotes a marine expert who posits the fact that ‘China has developed mechanical systems such as an 'ocean towing type cutting device' and a 'towed submarine cable cutting device and cable cutting method thereof' suggest that Beijing is keeping multiple technical options in its arsenal for manifesting seabed warfare threats toward subsea energy and telecommunications infrastructure worldwide’.

Jocelinn Kang in ‘Subsea communications cables: vital but vulnerable’, endorses the assessment that the biggest threats to subsea cables come from human activities, citing data from 2007 to 2018 demonstrating that anchors and fishing account for more than three-quarters of known cable faults. The damage occurs as anchors are dragged across the ocean floor or when bottom trawling fishing equipment entangles the cables. Kang highlights that while this is usually accidental, it could be done intentionally. Proving intention, however, can be challenging.

Kang urges protective measures. These include physical security measures, such as making cables with armour and burying cables in shallower areas to reduce the risk of damage, but also limiting access to cable landing stations where cables come ashore and are more vulnerable. Cybersecurity of the software that manages the cable network, and auxiliary systems such as security camera networks protecting cable landing stations, and network operation centres, are also essential. Further, Kang stresses that a repair capability is vital, particularly repair ships, but bemoans that there are only around 70 cable ships worldwide, and only a third are set up repairs. All this presents a significant challenge in maintaining cable system resilience. Kang references a separate report that assesses Australia’s subsea capable resilience as generally good but with persisting challenges. Kang argues for investment in enhancing physical and cybersecurity measures and repair capabilities.

In ‘Working to protect undersea infrastructure’, Commander Ian Jackson of the Australian Department of Defence announced the importance Australia is attaching to the issue of countering subsea and seabed warfare (SSW). In the statement, the ability to monitor and protect Australia’s undersea critical infrastructure is recognised as vital to Australia’s domestic security and prosperity. In February 2025, the Royal Australian Navy deployable undersea warfare forces joined the US Navy and Royal Navy in furthering SSW in an AUKUS Pillar II Undersea Warfare advanced capabilities event at Norfolk, Virginia. SSW focuses on Navy understanding and exploiting the entire water column from the surface to ocean floor to monitor, protect and defend Australia’s undersea critical infrastructure. AUKUS Pillar II, an agreement between Australia, the UK and the US, promotes the development of advanced technologies and the integration of capabilities across the partner nations. Jackson notes that undersea warfare is one of the agreed areas of focus of AUKUS Pilar II and SSW is at the vanguard of this effort, using advanced technology (robotic and autonomous systems using artificial intelligence and machine learning enabled systems) to exploit and understand the undersea environment. Jackson comments that collaborative exercises will continue as the AUKUS partners refine their skills in undersea warfare advanced capabilities in 2025.

In ‘What lies beneath: There’s more to cables than geopolitics, Cynthia Mehboob decries the narrow focus on national security in addressing the vulnerability of subsea critical infrastructure. In September 2024, during the UN General Assembly High-Level Week, the US, EU and their allies unveiled the New York Principles on Undersea Cables, committing to bolster the security and resilience of global networks, especially by encouraging the avoidance of high-risk suppliers. The principles were endorsed by 30 nations, including Australia. But Mehboob Fargued that other vital concerns, such as those around deep-sea mining and environmental impacts, are neglected. In her view, the focus on national security glosses over the complex material and environmental challenges in managing these critical systems, creating regulatory uncertainty for private actors. Mehboob highlights that industry is achieving more substantive cooperation than governments on tackling the real-world challenges of building and maintaining resilient infrastructure.

Lieutenant Robert Rushby