Subsea cables carry more than 99% of global internet traffic and make up more than £1.4 trillion (US$1.87 trillion) in daily financial transactions in the UK. Yet, this critical infrastructure faces growing threats from hostile state actors, which has exposed how vulnerable internet infrastructure can be.

The UK government announced plans in May 2026 to improve protection for subsea internet cables amid heightened Russian activity in the country’s waters. Guidance included new obligations on subsea cable operators to secure their infrastructure, with new emergency powers for the government expected to be proposed after heightened suspicious activity.

Capacity spoke with RETN CEO Tony O’Sullivan on the subject, who called for greater awareness now that the risk landscape has changed.

“Accidental damage is no longer the only threat, and operators and enterprises can no longer assume routes are safe and stable when assessing resilience,” he explained. “Rather, you have to engineer it into the network itself. Route diversity is a must to avoid creating single points of failure, as is ensuring visibility across international paths.

“Rather than trying to prevent disruption, we have to design networks to cope with it.”

Context: How the global subsea threat landscape has changed

Cable faults often happen from accidents like fishing, ship anchors and equipment failure, among other things. However, O’Sullivan explained to us that the context in which these faults occur has changed, amid rapid deployment of submarine infrastructure driven by hyperscalers, AI and cloud growth, the desire for additional routes and the need for constant connectivity through the cables.

“[These changes] are not accompanied by an expansion of repair capabilities, which can only be carried out by 60-80 dedicated ships worldwide, with several of them rather outdated,” he said. “Furthermore, due to heightened political tensions between nations, there are some crucial chokepoints, such as the Baltic Sea, Red Sea, or Taiwan Strait, that pose some risk because repair work might be hindered by political tensions.”

He added: “What is truly different in today’s risk landscape is not simply the concern about deliberate attacks, but the anxiety regarding recoverability – in the end, a cut is a cut.”

For instance, the ongoing war with Iran has halted at least three major undersea cable projects in the Persian Gulf. O’Sullivan believes this exposes a much deeper structural problem with how concentrated subsea infrastructure really is.
“The industry likes to call underwater cables global networks, but in reality, most internet traffic passes through just a few narrow corridors – and everyone knows where they are. The Red Sea, the Gulf of Oman, parts of the East China Sea, and the Strait of Dover are good examples,” he explained. “Given the volume of traffic that runs along these routes, if they do get affected, it would not just affect the edge of the internet backbone, but a major conduit.”

He added that the ongoing conflict makes clear that building more cables along the same corridors does little to help build resilience. Instead, he calls for a mix of submarine and terrestrial routes that are diversified across geopolitical regions.

“We need to choose different routes, not a different cable in the same corridor,” he said.

Why UK infrastructure remains vulnerable

The UK is a leader in global submarine cable networks, with multiple landing stations (roughly 64 cables) and a resilience that ensures business-as-usual rerouting without causing service interruptions.

While faults are often not malicious, the UK government has indicated that suspicious activity near its cables is increasingly being observed. O’Sullivan suggested a rethink is needed.

“The value of these cables from the perspective of resilience does not depend only on the presence of these resources, but rather on traffic distribution in these channels,” he explained. “It is possible for a significant volume of traffic to utilise fewer efficient and cost-effective lines. Concentrating traffic on a limited number of routes, even with a large number of physical measurements, can create a disproportionate risk if they are disrupted.”

While government bodies and businesses are working hard to increase resilience further, some links are still vulnerable. O’Sullivan cited remote islands, military and financial networks as examples.

“To sum up, business-as-usual resilience in the UK is impressive; yet, there is still work to be done by governmental institutions and industry leaders,” he explained.

If the internet were to fail in the UK, it would result in significant problems like payment systems, stock exchanges and cloud computing services going down. In severe cases, there could be payment and supply chain failures, degraded communications and emergency response being overstretched.

“Consider how latency-sensitive services will be impacted by having transaction and banking data sent through significantly longer routes, for instance,” O’Sullivan noted. “There are various sectors whose activities depend on a constant internet connection, such as energy grids and health care, and logistics management systems.”

Building resilience in a changing threat landscape

To build greater subsea resilience in the UK, collaboration between UK businesses and the government is paramount. O’Sullivan suggested that an organisation should first identify the most important data flows and ensure contingency plans are in place for each one.

“This means having another route through a separate landing station with another service provider,” he explained. “The government may help in this by introducing incentives and standards, while companies share best practices.”

UK Finance has also suggested creating channels for sharing threat information and organising scenario exercises, O’Sullivan added. He suggested the government could help in this instance by facilitating the planning of new routes and investing more in strategic assets like repair ships.

Importantly, though, public-private partnerships on infrastructure resilience will ensure successful long-term threat response.

“Education and transparency form the core elements of an effective partnership between the private and public sectors on building resilient infrastructures,” O’Sullivan added. “The truth is that resilience already exists within the global infrastructure network, but the problem lies in the fact that many do not understand the existing resilience in place.”

He explained that companies often take resilience for granted because they can see diversity on the map. However, O’Sullivan explained that their traffic flows on a much smaller number of paths designed to optimise costs.

“The key point is to start educating operators and customers on the true nature of the existing network,” he said. “Once that’s done, behaviours can change. Whereas one needs to raise customer expectations regarding what infrastructure-level thinking looks like, the other is responsible for educating the market on proper provisioning of networks and managing concentration risks.”

This is also why route diversity is a strong part of building resilience against threats. True diversity is ensuring data is physically transmitted on separate routes, rather than on multiple cables that run alongside each other.

Although this sounds logical in theory, O’Sullivan told us it’s actually a difficult and rare practice within the sector. In fact, a study by RETN found that many routes that claim diversity actually converge onto the same fibre infrastructure.

“Industry-wide, few operators invest equally in fully separate backup routes because it’s expensive,” he said. “Although the buzzword ‘diverse’ is common, actually delivering it at scale is still the exception, not the norm. We encourage businesses to scrutinise their paths – ask your carriers: “Do these cables really go different ways?” – because superficial diversity may not protect you in a true crisis.”

Confronting risk

Some businesses may feel uncertain about which step to take first. O’Sullivan’s advice is simple: “Don’t wait, start small and build out”.

RETN operates with resilience at the core of its philosophy, he explained, as the company operates its own DWDM backbone network. This includes routes deliberately made distinct to its target hubs.

“To give you an idea, our newest line between Romania and Moldova offers a totally new route in Eastern Europe, thus ensuring higher route diversity for our clients. This translates into switching to another cable, usually in another country, when one gets sliced,” O’Sullivan added. “RETN offers its clients various redundancies and exceptional uptimes of their infrastructure.”

The company has also committed to spreading knowledge about subsea issues and regularly talks about creating ‘hardwired for chaos’ networks, as O’Sullivan refers to them.

“We are well-positioned to support UK digital resilience, whether by consulting on route diversity or providing alternate transit if primary paths fail,” he added.

Looking at the pig picture, O’Sullivan advised that businesses find out what its important services are and see how they connect to the internet. He suggested at least two separate connections or providers for each service must be present to prevent a company from losing the ability to work.

“Many businesses already do this in practice. You can start with understanding your potential vulnerability and proceed to diversification, which means investing in at least a minimum number of connections/providers,” he explained. “Then test failover during off-hours.

“Remember: resilience is a journey, not a switch you flick. By taking action now – however modest – you’ll improve your readiness far more than doing nothing and hoping for the best.”

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