ASW in a Box: How UK and Dutch Containerised Sensors Plan to Expose Russian Submarines in the Channel

The Royal Navy is facing a basic numbers problem.

At the end of the Cold War, Britain had about 50 frigates and destroyers and around 30 submarines. Today, it has six Type 45 destroyers and five Type 23 frigates. The submarine fleet includes six Astute-class attack submarines and four Vanguard-class ballistic missile submarines.

More ships are being built, including Type 26 and Type 31 frigates. But they cannot solve an immediate shortage.

Meanwhile, Russian naval activity around Britain has increased. Activity in British waters rose by about 30% between 2024 and 2026. During 2025 and 2026, the Royal Navy carried out 116 missions to follow Russian warships and commercial vessels linked to the shadow fleet.

In July alone, British forces spent 21 days continuously monitoring Russian naval movements.

That requires ships, helicopters and crews. And those assets cannot be everywhere at once.

This is where a relatively small sensor system could make a difference.

What is “ASW in a box”?

OptiArray is essentially a towed acoustic sensor that comes in a 10-foot shipping container.

The system uses fibre-optic hydrophones to listen for sounds underwater. Unlike traditional electronic systems, it does not produce an electromagnetic field or electronic noise. It also does not need external power from the vessel carrying it.

That makes it easier to install on platforms that were never designed for anti-submarine warfare.

The system can reportedly detect large oil tankers at distances of up to 100 kilometres and frigates at around 50 kilometres in favourable conditions. Loud unmanned surface vessels can be detected at distances of tens of kilometres.

Those numbers need to be treated carefully.

The actual range depends on water depth, temperature, underwater conditions, background noise and the type of vessel being tracked. A large tanker is much easier to hear than a quiet modern submarine. The busy and relatively shallow waters of the English Channel make the problem even more complicated.

So the important point is not that one container can “see” everything within a 100-kilometre radius.

Its value comes from putting many sensors in the water.

A network instead of a few expensive ships

The Dutch Ministry of Defence has already awarded Optics11 a contract for containerised arrays that can be used on manned and unmanned platforms.

The company is also developing OptiBarrier, a static seabed system intended to monitor critical infrastructure such as energy pipelines and data cables.

Britain is considering taking the idea further by putting similar passive sensors on commercial cargo vessels operating in the English Channel and North Atlantic.

That would change the way maritime surveillance is organised.

Instead of asking a frigate to follow every suspicious vessel, some of the initial monitoring could be done by commercial ships, unmanned vessels and fixed sensors. Military platforms could then be sent to investigate contacts that actually require them.

This matters because Russian activity is not limited to conventional warships.

British forces have been monitoring Russian naval vessels as well as commercial ships associated with the shadow fleet. In June, UK authorities intercepted the sanctioned tanker Smyrtos in the English Channel.

Russian warships have also been moving through European waters. The destroyer Admiral Levchenko and frigate Neustrashimy escorted a sanctioned cargo vessel and oil tanker through the Baltic and English Channel towards Egypt. The frigate Admiral Kasatonov, armed with Zircon hypersonic missiles, was deployed near Germany's Fehmarn Island.

Then there is the underwater threat.

Russia has begun sea trials of the nuclear-powered Khabarovsk submarine, which is designed to carry up to six Poseidon autonomous nuclear-powered torpedoes.

For Britain and its allies, the problem is therefore not simply counting Russian warships. It is maintaining awareness of what is happening above and below the water.

Why cables are becoming part of the problem

The growing interest in underwater sensors is also linked to the vulnerability of subsea infrastructure.

Underwater cables carry 99% of international data, while pipelines are critical for energy supplies. Protecting them requires knowing what is happening around them before an incident occurs.

Fixed seabed sensors such as OptiBarrier could provide permanent monitoring around particularly sensitive areas. Mobile systems on ships could cover wider areas and move when needed.

Unmanned surface vessels could add another layer without putting a crew at risk.

None of these systems is a replacement for a frigate or submarine. But they could reduce the number of times those expensive platforms have to perform routine monitoring.

That is important for a navy with only 11 destroyers and frigates available for this kind of work.

The civilian shipping problem

Putting military sensors on commercial ships also creates a difficult question: what happens to those ships if a conflict begins?

A cargo vessel carrying an acoustic surveillance system may still look like an ordinary civilian ship. But if it is collecting military information, an adversary could view it differently.

That creates potential legal questions about the status of such vessels during armed conflict.

There are also practical problems. Who receives the information? Who controls it? How is sensitive data protected? What happens when a commercial vessel enters another country's waters?

The crews themselves could also be placed in a difficult position. They may work for a commercial company, yet the ship could be performing a task with clear military value.

The same feature that makes commercial vessels attractive - their large numbers and constant movement - could therefore create new risks.

A way to buy time

Britain has already allocated £1.5bn to a hybrid fleet that will include uncrewed sensor and missile ships. It is also spending £330m over four years on protecting critical subsea infrastructure.

OptiArray fits into this wider effort.

The system does not solve Britain's shortage of warships. It does something more modest but potentially useful: it allows the Navy to put more eyes and ears into the water without building a new frigate for every surveillance mission.

That could be especially valuable in the English Channel and North Atlantic, where Russian warships, shadow-fleet vessels, commercial shipping and critical infrastructure all share the same increasingly crowded waters.

The bigger change is that anti-submarine surveillance is no longer being designed entirely around specialised naval vessels. Sensors can be placed on unmanned craft, fixed to the seabed or carried by commercial ships.

For a navy struggling with numbers, that is an attractive proposition.

But it also means that the line between civilian shipping and military infrastructure is becoming harder to draw - and that may become one of the most difficult consequences of turning the commercial fleet into part of Europe's maritime surveillance system.