Exploiting the underwater battlespace: Part 1 – characterising the subsea threat

In the modern world, most of us probably assume that the ubiquitous nature of today’s wireless communications renders reliance on physical infrastructure a thing of the past. The truth is actually quite the reverse. 

More than ever, we are dependent on networks of undersea cables which travel across the seabed to connect countries, companies and individuals around the world. This infrastructure enables us to communicate globally and keeps entire industries running; various estimates suggest that subsea cables carry more than 95% of global internet traffic and facilitate more than $10 trillion of financial transactions daily. Our reliance on them even extends to power, oil and gas which – together with communication networks – present an attack surface that we cannot afford to leave unprotected.

In short, subsea cables represent critical infrastructure that is indispensable for national security purposes and to a fully functioning modern society. And they are facing increasing threats – both in terms of frequency and severity – ranging from accidental damage to deliberate sabotage. In this first blog in a three-part series exploring the underwater battlespace, we outline the backdrop to the modern subsea threat. 

An increasingly contested domain

To quote from a recent Policy Exchange paper, “From Seabed to Space”, released in 2024: “Technological and operational developments have brought geopolitical competition to the seabed. As the ability to manoeuvre, map and operate at greater depths increases, critical maritime infrastructure along the seabed resembles the exposed underbelly of national security in a new age of undersea warfare.”

Clearly, the threat is significant and concerning. While undersea warfare is nothing new, recent incidents have served as a wake-up call regarding the growing threat to critical infrastructure on the seabed and the resulting risk to national security. 

For example, in November 2024 two fibre-optic cables running under the Baltic Sea from Germany to Finland and Sweden to Lithuania were severed, followed by Estonia’s power supply being significantly impacted when the main undersea electricity cable linking Finland with Estonia was damaged. These incidents highlighted the Baltic region’s status as a global centre for suspected subsea infrastructure sabotage over the last few years.

This spate of incidents recently prompted NATO to launch a new mission called "Baltic Sentry", increasing surveillance of ships in the Baltic Sea with aircraft, warships and drones in an effort to protect these crucial undersea cables at a time when geo-political tensions have never been higher.

One of the key challenges facing governments is that the maritime threat is evolving beyond traditional domains to incorporate more grey-zone, sub-threshold tactics and strategies as necessary vehicles for delivering effect and maintaining the competitive edge. Threat levels are increasing, a wider group of sophisticated adversaries are emerging, and the pace of change is only expected to accelerate. 

And, with the ocean covering more than 70% of our planet, it is challenging to secure such a large area – particularly in a persistent, cost effective manner that prioritises sensors, platforms and effectors in a way that allows us to detect and deter interference before it happens.

Characterising the threat

Three capability areas are becoming ever more important due to the increasing threat. These are: Intelligence, Surveillance and Reconnaissance (ISR); Anti-Submarine Warfare (ASW); and Critical Undersea infrastructure Protection (CUIP). Not only are governments and commercial operators seeing an exponential increase in threats in these key areas, but they are facing the realisation that traditional, conventional capabilities and countermeasures are becoming less and less relevant and effective.

In ISR, the risk appetite to deploy a crewed submarine to conduct up-threat tasking is low, and in certain operational scenarios, not possible. Yet the need to gain intelligence early from strategically positioned indicators and warnings, that give a competitive advantage over adversaries in the underwater domain, is only increasing. 

Similarly, the demand for information and intelligence to inform timely decision-making to counter the ASW threat in multiple regions, simultaneously and persistently, is significant. In fact, the sheer scale of this challenge outmatches many nations’ current force structures.

Overlaid on these threat vectors is the growing risk to CUI, on which so much of global economic activity and prosperity relies. Whilst this critical infrastructure has traversed the globe for decades, it has until the recent past been largely unreachable and therefore unrecognised as a target of adversary effort. As we know from national and international media, the undersea character of conflict is now changing, and vulnerabilities in CUI are being actively targeted.

Ultimately, humanity’s growing ability to manoeuvre, map and operate at greater depths is putting critical maritime infrastructure along the seabed – a backbone of national security and resilience – increasingly at risk a new age of undersea warfare. What’s more, the pivot to uncrewed platforms is making the threat even more potent. 

So, how can we counter the threat to subsea cables? Stay tuned for the next blog in our ‘Exploiting the underwater battlespace’ series, where we’ll outline what the UK needs to do to enhance its subsea threat response and why a vital capability gap could be hindering progress.