What Defence Stakeholders Need to Know When Protecting Critical Undersea Infrastructure

Often overlooked, the battle space beneath the waves is nonetheless a vital component of modern-day defence strategy. Undersea infrastructure and offshore energy links have become vital targets for adversaries, and for good reason. It is up to defence, government and industry stakeholders to build resilience against threats that hold the power to destabilise both security and economy. 

Why undersea infrastructure is a defence priority in 2025

Subsea data cables, energy interconnectors and pipelines to offshore wind export links, seabed sensors and cable landing stations are all examples of undersea infrastructure. These assets are essential to global economies because they support military command, intelligence backhaul and the delivery of fundamental services. 

When undersea infrastructure is disrupted, it causes severe economic aftershocks and jeopardises C2ISR (command, control, intelligence, surveillance, reconnaissance) networks. As RAND reports:

“Disruption to a subsea telecommunications cable can cost more than 24 million euros per day and often take up to three weeks to fix, resulting in an overall cost of at least 504 million euros.”

Threats now include:

-State or proxy probing – hostile nations test defences by loitering near cables or mapping routes under the guise of routine activity.
-Small, quiet UUVs/AUVs –underwater drones can now discreetly tamper with or monitor undersea infrastructure.
-Camouflage under commercial activity – sabotage can be hidden behind normal fishing or shipping operations.
-Cyber-physical attacks at shore facilities – hackers target cable landing stations on land, disrupting operations without touching the seabed.
-Attribution and plausible deniability – damage can easily be blamed on accidents or natural events, making sabotage hard to prove.

Recent incidents in the Baltic and Taiwan (whereby suspected Russian and Chinese vessels severed subsea cables during 2024–25) emphasise how vast and difficult to monitor the undersea domain truly is, not to mention the added risks created by patchy international rules.

Technologies used for seabed observation and situational awareness

We know that the seabed is a complicated area to monitor – its mere location alone proves the point. Overcoming that difficulty through seabed observation strategies, however, allows for early detection, verification and reaction to potential threats. Here are a few ways it can be done:

Persistent sensing is the foundation of undersea visibility. Distributed Acoustic Sensing (DAS) is an example of an innovative technology which has the power to turn fibre-optic cables into long acoustic sensors which detect vessel activity, anchor drags, and other disturbances along priority routes. John Potter, professor at the Center for Geophysical Forecasting in Norway, explains “[DAS can] detect, localise and classify a ship, including stern and bow waves… [and] something dragging across the seabed independently. That could include anchors, which have been blamed for cutting undersea cables.” 

On the other hand, we have mobile surveillance, which extends the reach and flexibility of USVs and AUVs. Assets are equipped with interchangeable sensor packages (such as synthetic aperture sonar, optical cameras, and magnetometers) that can investigate unusual cues along the seabed. Companies like Cellula Robotics[6] have developed long-endurance AUVs that can be fitted with various sensors, illustrating how platforms such as these can be used for both commercial and defence purposes.

Space and surface fusion can also enhance situational awareness. Satellite AIS, synthetic aperture radar (SAR), and space-based RF analytics can flag abnormal behaviour around cable corridors and landing approaches - this includes ‘dark’ vessels (ships who operate without transponders). In 2019 space-analytics firms ICEYE and Spire joined forces to demonstrate this in practice, combining SAR imagery with satellite AIS to detect non-cooperative vessels. Their collaboration intended to uncover trafficking and illegal fishing whilst simultaneously offering governments a “a new and increased ability to monitor maritime traffic, including vessels that want to avoid detection” – Pekka Laurila, ICEYE’s co-founder.

What happens after detection? Turning sensing into action

An effective defence of seabed assets relies on a layered concept: deter, detect, delay, and respond (with indeed the very act of observation itself acting as a valuable deterrent.)

Deter & detect

At the forefront of seabed defence sits the “picket.” In this context (because it varies depending on the domain) a picket is a type of USV that patrols and performs as an early warning system. While its primary role is to detect suspicious activity around critical undersea infrastructure, pickets can also cue closer inspections by autonomous or remotely operated vehicles. Other deterrents include landing stations, exclusion zones, and tamper-evident covers.

Delay

When the inevitable breaches do occur, resilience by design significantly delays disruption and helps prevent adversaries a quick win. This is achieved via diversified cable routes, mesh networks, and built-in traffic rerouting ensure that operations continue even during partial losses.[9] Wet-mate connectors with universal joints also allow for faster repairs.

Respond 

Preplanning and a quick reaction time are equally important. This is achieved via various tools such as pre-positioned spares, clamps, repair kits, solid repair vessel contracts or SLAs, and deployable ROV toolkits[10]. Finally, shore-based cyber safeguards protect the digital systems that support critical undersea infrastructure. Network segmentation, multi-factor authentication, telemetry protection, and supply-chain security help strengthen the cyber layer so that attackers cannot exploit digital weaknesses.

Governance and collective defence of the seabed 

Seabed protection will never be just a matter of technology and strategy. Law, governance and cooperation across boarders plays a huge role. 

According to the UN Convention on the Law of the Sea (UNCLOS), coastal states hold jurisdiction over their territorial sea (up to 12 nautical miles) and Exclusive Economic Zone (EEZ). However, beyond that, such as in the high seas, monitoring, enforcement, and pursuit of threats are far more limited[11]. This legal complexity means that countries need to work in an interoperable manner by agreeing on standards for evidence and setting up clear communication to support deterrence. 

Actionable information exchange relies on straight forward processes for handling data. Data must be classified properly, shared in a secure matter and delivered in a standard format so military, coast guards and agency partners can all use it. Last month’s MARSEX EU 25 (2025) exercise is a useful example; European navies, coast guards, and agencies such as FRONTEX and EMSA used platforms like CISE and MARSUR to coordinate responses to simulated sabotage of underwater pipelines. These exercises are beneficial as they validate operational systems and improve interoperability against threats in the real world. 

Open standards are important too. Common data models and agreed underwater communication protocols do well in supporting interoperability between assets from different nations and suppliers, as well as ensuring compatibility between military and civilian platforms. Notably, we have NATO’s JANUS standard for acoustic communication, which is;

“a digital underwater signalling system that can be used to contact underwater devices using a common format; announce the presence of a device to reduce conflicts; and enable a group of underwater devices… to organise themselves into a network,” 

Fundamentally, this common ‘language’ allows otherwise incompatible systems to cooperate effectively in protecting critical undersea infrastructure.

Buying smart and proving readiness 

Smart investment – that’s the goal here. Buying the latest technology will not do well in protecting critical undersea infrastructure if it lacks the ability to withstand harsh maritime environments whilst performing under pressure. Procurement demands interoperability. This is achieved through open APIs and data rights, reliability in cluttered littoral zones, and transparent lifecycle costs.

Here is a quick readiness checklist: 

·       Real-time awareness of priority routes and landing sites?

·       Are spares, repair vessels, and SLAs pre-positioned and exercised?

·       Independent route alternatives and rerouting plans?

·       Pre-agreed classification and data-sharing protocols with operators and allies?

·       When was the last multi-agency seabed incident rehearsal, and what was the measured response time?

·       Are evidence handling and escalation playbooks clear and practiced?

·       Are cyber safeguards integrated with physical protection measures?

·       Is operator and crew training current and refreshed regularly?

Using this approach ensures both procurement discipline and operational readiness. As RAND stresses, operators must be the first line of defence, designing resilience in from the start and sharing anomalies with authorities such as NATO’s Critical Undersea Infrastructure Coordination Cell.

Bibliography

Atlantic Council. Cyber Defense across the Ocean Floor: The Geopolitics of Submarine Cable Security. Available at: https://www.atlanticcouncil.org/in-depth-research-reports/report/cyber-defense-across-the-ocean-floor-the-geopolitics-of-submarine-cable-security. Accessed August 20, 2025.

Cellula Robotics. Unmanned Systems Technology. Available at: https://www.unmannedsystemstechnology.com/company/cellula-robotics. Accessed August 19, 2025.

EIS Council. “The Emerging Threat to Undersea Infrastructure.” 2025. Available at: https://eiscouncil.org/the-emerging-threat-to-undersea-infrastructure. Accessed August 18, 2025.

The Guardian. “Risk of Undersea Cable Attacks Backed by Russia and China Likely to Rise, Report Warns.” July 17, 2025. Available at: https://www.theguardian.com/technology/2025/jul/17/risk-undersea-cable-attacks-backed-russia-china-likely-rise-report-warns. Accessed August 21, 2025.

ICEYE. “ICEYE and Spire Join Forces to Enable Global Monitoring of Dark Vessels at Sea.” Press Release. Available at: https://www.iceye.com/newsroom/press-releases/iceye-spire-join-forces-enable-global-monitoring-dark-vessels-at-sea. Accessed August 22, 2025.

Leadvent Group. “Subsea Cable Maintenance: Repairing, Improving Reliability and Avoiding Downtime.” Available at: https://www.leadventgrp.com/blog/subsea-cable-maintenance-repairing-improving-reliability-and-avoiding-downtime-1. Accessed August 20, 2025.

LinkedIn. Louis Barani. “Deter, Detect, Delay, Respond: Core Functions of Security Add.” Available at: https://www.linkedin.com/pulse/deter-detect-delay-respond-core-functions-security-add-louis-barani-bh1le/. Accessed August 22, 2025.

National Defense Magazine. “Sensors, AI Possible Solutions to Preventing Undersea Cable Sabotage.” May 13, 2025. Available at: https://www.nationaldefensemagazine.org/articles/2025/5/13/sensors-ai-possible-solutions-to-preventing-undersea-cable-sabotage. Accessed August 18, 2025.

NATO. “NATO to Boost Maritime Security Cooperation.” News release, March 15, 2017. Available at: https://www.nato.int/cps/en/natohq/news_143247.htm. Accessed August 21, 2025.

Public Now. “Global Subsea Security Report.” 2025. Available at: https://ebs.publicnow.com/view/7E48A8AAFF72E0D31AB52CAE238538BBA9BD5DC2. Accessed August 22, 2025.

RAND Corporation. Protecting Europe’s Critical Undersea Infrastructure. June 2025. Available at: https://www.rand.org/pubs/commentary/2025/06/protecting-europes-critical-undersea-infrastructure.html. Accessed August 19, 2025.

RAND Corporation. Perspectives on Seabed Security. PEA3800-1. Available at: https://www.rand.org/content/dam/rand/pubs/perspectives/PEA3800/PEA3800-1/RAND_PEA3800-1.pdf. Accessed August 20, 2025.

Recorded Future. “Submarine Cables Face Increasing Threats.” 2025. Available at: https://www.recordedfuture.com/research/submarine-cables-face-increasing-threats. Accessed August 21, 2025.

Tufts University. Law of the Sea, Chapter Two. Available at: https://sites.tufts.edu/lawofthesea/chapter-two. Accessed August 19, 2025.