Protecting maritime infrastructure from attack: new technologies and tactics

In this guest article, Kamil Sadowski considers the challenges of protecting the maritime infrastructure which underpins much of Europe’s economic activity and is increasingly seen as a major vulnerability for many NATO nations.

Ensuring the security of naval bases, commercial ports and harbours, pipelines, cables, and other installations is becoming a higher priority. This is particularly true in the underwater domain, which offers the greatest scope for inflicting severe damage discreetly.

A noisy underwater environment is a natural ally for sabotage operations, with the Baltic Sea being a prime example of such conditions. Dense marine traffic provides acoustic camouflage for the stealthy insertion and recovery of all kinds of underwater assets.

The scale of the problem also varies depending on the location of protected facilities. Installations located in territorial waters or restricted areas (where navigation is difficult) present are a significantly different challenge compared to those in open waters such as the extremities of many Exclusive Economic Zones (EEZ).

Threat vectors

Stealth and deniability is the defining feature of seabed warfare, making early detection difficult and post-incident analysis equally challenging, whether the effects are damage or the installation of spy equipment. New technologies have also multiplied the threat and lowered the bar to entry beyond traditional state actors.

Known cases of suspicious activity involve surface vessels equipped with systems capable of seabed operations, observed near areas where underwater cables are laid. Such operations inevitably leave traces, and over time, collected data can reveal the full picture. Consequently, maritime traffic control systems are evolving to implement tools for early detection of suspicious behaviour. The situation becomes even more complex when operations occur entirely or predominantly beneath the surface.

The very long endurance of extra-large unmanned underwater vehicles (XLUUVs) makes it possible for them to transit from distant areas, including potentially from an adversary’s territorial waters. When stealth is critical, the force delivery role may be undertaken by submarines (including midget submarines), presenting the most challenging scenario for infrastructure protection.

Generally, the first category of adversary assets (force delivery units) will attempt to remain outside the surveillance zones of underwater systems protecting mission objectives. Their task is typically to approach to a safe distance before deploying embarked mission assets. Submarine presence is notoriously hard to detect, especially for early warning or real-time awareness.

The second category of assets comprises mission execution or close support assets, which require closer interaction with targets. Midget submarines, better suited for shallow water operations, occupy a space between the two categories. These assets constitute primary targets for systems dedicated to infrastructure protection, leaving broader anti-submarine warfare (ASW) efforts to naval forces.

Among this group, large UUVs pose distinct challenges. Being uncrewed, they offer significantly greater endurance and tolerance for operating in high-risk areas, making them ideal for Intelligence Preparation of the Operational Environment (IPOE) or for delivering equipment in advance of sabotage missions.

Many future concepts envision expanding the range of tasks that can be performed solely by unmanned assets. While human supervision may still be needed for highly precise activities, over time it may become possible to remove the human presence from the mission entirely. Future XLUUVs equipped for such operations could complete entire missions without the weak link – the human diver, and could turn the tables by being a threat to the adversary.

Fixed undersea surveillance systems

Active sonar systems designed to detect divers, commonly known as Intruder Detection Sonar (IDS) or Diver Detection Sonar (DDS), operate typically in the 60–90 kHz frequency band. Advanced signal processing allows automated detection and classification of divers and similarly sized targets. These systems achieve surveillance ranges of approximately 400–800 metres against divers (depending on open or closed-circuit breathing systems) and up to 1500 metres for XLUUVs. They provide reliable automated awareness and crucial reaction time to counter threats. IDS is deployed in harbour approaches and suspended from ships to provide coverage in unprotected areas and anchorages.

Passive sonar systems typically form layered barriers to monitor both near zones and outer areas. Passive surveillance is more challenging than active, requiring complex Low Frequency Analysis and Recording (LOFAR) techniques that are difficult to automate, and are more sensitive to ambient noise. Although passive systems offer limited real-time awareness against very silent targets such as submarines or UUVs, they are critical for long-term surveillance, acoustic intelligence gathering, and providing forensic evidence in case of an incident. Fibre-optic hydrophones, with flexible deployment and minimal maintenance needs, are increasingly used.

The optimal setup for underwater surveillance combines both active and passive sonar systems to maximise coverage and data collection. Other technologies such as Distributed Acoustic Sensing (DAS) and magnetic anomaly detectors also play important roles, particularly in areas where dense sensor coverage is not economically viable. DAS, for example, is well suited to monitoring activities near underwater cables.

Security augmentation with unmanned assets

Even if critical infrastructure facilities are well monitored, large areas, such as the spaces around pipelines and cables, remain vulnerable. Technologies like DAS help extend coverage, but gaps and limitations persist, providing opportunities for adversaries.

While infrastructure protection is a task for maritime forces, no navy has the luxury of dedicating sufficient warships and maritime aircraft exclusively to this role. Naval assets cannot be permanently assigned to infrastructure protection, and they are not proportional responses to threats like small underwater assets. Furthermore, traditional ASW sensors and effectors are not always suitable for detecting these targets.

This reality creates space for unmanned assets to augment the surveillance network and support rapid response capabilities. Properly equipped, they can become equivalent forces against the types of threats described.

Small Unmanned Surface Vehicles (USVs) – up to 12 metres in length – were among the first uncrewed platforms developed for tactical maritime warfare roles. Their compact size, endurance, modularity, and payload options make them suitable for many mission profiles, particularly those requiring lengthy operations like ASW and seabed warfare. Adaptations to ASW, using USVs as either sensor platforms or even ASW weapon carriers, are already mature.

Similar adaptations could be made for infrastructure protection missions. Active IDS provides a promising lightweight sensor base for USVs optimised against underwater threats. Importantly, USVs typically have a significant speed and manoeuvrability advantage over submersibles.

USVs can be configured with deployable packages that are lowered into the water offering reliable automatic detection like combination of IDS with deterrence loudhailer. Because IDS transmit frequency is operating outside human hearing ranges, this combination enables not only detection but also immediate deterrence if a diver is recognised.

Another option involves Intruder Detection – Variable Depth Sonar (ID-VDS), allowing for continuous slow-speed searching instead of the ‘leapfrogging’ between dipping stations. The choice between dipping sonar or VDS depends on the operational area and mission profile. As with ASW adaptations, both systems may be needed to optimise surveillance coverage.

Equipped in this way, USVs can investigate suspected underwater activity and augment fixed surveillance systems, helping to seal coverage gaps. They represent a mobile component vital to the protection network, and there is potential for future USV-based force protection assets to be embarked aboard warships or other vessel of opportunity.

Kamil Sadowski served as an officer in the Polish Navy for 21 years specialising in ASW and has experience of developing and deploying underwater weapons systems.