DSEI 2025: SEA, KraitSense, and the ASW gap

The UK company SEA has signed an MoU with ACUA Ocean to explore the deployment of its KraitSense passive sonar to ACUA autonomous surface vessels. Calibre Defence met with Darren Boyle, Technical Director from SEA to learn more about the company’s capabilities and how they can help fill the ASW gap. But to understand the scale of this challenge, it is important to first look back at how this capability has changed.

2.5 million square kilometres: that is the surface area of the Norwegian and Greenland Seas combined. Together, they are the gateway to Europe and the Atlantic for Russian submarines from the Northern Fleet. Patrolling and defending these bodies of water is critical to Europe’s way of life and security, but doing so is resource intensive and difficult. In the 1980s, as the threat of the Soviet Union began to recede, the Royal Navy was almost as large as the British Army is today, with some 57,000 personnel and 7,000 marines. 

They were deployed across 50 surface vessels, including the Type 21 and 22 frigates, as well as the Leander class and Type 42 destroyers, all of which had some form of anti-submarine warfare (ASW) capability in the shape of torpedoes and sonar. In addition, the Navy fielded six squadrons of Sea Kings specifically configured for the ASW role. Below the surface, there was a fleet of more than 30 submarines, providing attack and nuclear capabilities, as well as contributing to the hunt for Russian submarines. The Royal Navy was a fearsome presence in the North Atlantic: but much has changed since then – except for the surface area of the Norwegian and Greenland seas. 

Russia is using its submarines to stretch and test NATO’s defences. To be clear, there are far fewer Russian submarines than there were in 1980. There are a total of 24 submarines in the Northern Fleet, not all of which are operational. However, in the event of a war, they would represent one of the most significant threats to Europe. And even a modest surge of eight submarines would likely stress NATO’s ability to track them. This is why increasing ASW capabilities is so important, but the Royal Navy, and many others in the North Sea, have reduced their fleet sizes leading to a reduction in ASW capability. 

“We can’t build our way out of the ASW threat, and we face a recognised shortage of ASW operators,” Technical Director Darren Boyle from SEA told me during DSEI. He had just finished a seminar in the Naval Zone titled, Three Missions, One Truth: ASW, ISR & MSA operations – are we ready for rapid sonar deployment? The short answer is yes, the West has the technical capability to rapidly deploy a lot of sonars, but there is a gap between the capability and reality.

“We lack a CONOPS [CONcept of OPerations] for maritime uncrewed systems and need to look at adding ASW capabilities to different platforms,” Darren explained, before offering a solution: “Advances in miniaturisation are helping sonar to improve its performance. COTS solutions can provide a high-performance sonar in a compact form. This offers a new CONOPS with massed swarms of sensors alongside large conventional ASW platforms.” 

This is the drive behind SEA’s recent partnership with ACUA Ocean, which was announced during DSEI UK 2025. Under that MoU, the two companies have agreed to explore the integration of SEA’s towed array sonar systems onto ACUA Ocean’s uncrewed surface vessels (USVs). Specifically, this means SEA’s KraitSense underwater sensing product and its compatibility with ACUA Ocean’s autonomous platforms. The goal is to assess the potential for using this combined technology in ASW and ISR operations.

The MoU also outlines a framework for the companies to identify potential defence and commercial applications for the technology. SEA will support the integration of its sensor systems and will work with ACUA Ocean to develop operational concepts. 

Darren was clear that they are looking at the UK’s Project CABOT with interest. CABOT is looking for a contractor-owned, contractor-operated persistent ASW sensor solution. It has two phases, Atlantic Net and Atlantic Bastion, which are designed to rapidly improve the UK’s ASW credibility. “There is also the question of persistence; surface ships and SSNs have to return to base when they run out of resources required to keep a crewed platform (food). But low power, autonomous sensors can provide the persistence that a large vessel cannot. There is also the transit time, if you have a 100-day mission, it might take days to travel there and back,” Darren explained, reducing the operational duration.

It is worth noting that SEA do not see their systems as a replacement for large conventional platforms like the Type 26, they are very much complementary. But the idea is that getting sonar onto as many vehicles as possible will improve persistence and detection. In other applications, a small self-powered platform, was able to deploy and operate KraitSense for nine months. “For CABOT, we are trying to position ourselves as a sensor provider. We want to integrate our sonar system with  as many platforms as possible, afforded by the flexible scalable nature of our solution,” Darren said.

More sensors could be key, as sensing for ASW is also changing. Over the past 20 years, the trends in ASW have been towards passive sonar. This means that instead of emitting sounds, the sonars were just designed to receive sounds. But this is changing, and Darren has theories around how KraitSense can contribute to this new paradigm. “Passive detection against Yasen-class submarines is increasingly difficult, and this is driving a shift back to active detection. While Krait is a passive sensor, it can be used as a receiver so a transmitter can emit the noise and Krait can be used to receive that return and help with threat localisation,” he explained. 

KraitSense and training burden

Beyond the issue of platform persistence, a key challenge in anti-submarine warfare is the scarcity of trained operators, a problem that KraitSense also helps to address. In any application where an operator is required to listen to signals, you can be reasonably certain that they are very specialised. In both electronic warfare and sonar, operators will watch a waterfall screen looking for anomalies, recognised patterns, or even the absence of recognised patterns. They will know, from the sounds they are hearing or signals they are seeing, what is out there. In short, the UK RN ASW operators are highly skilled and incredibly effective in identifying contacts of interest. “Scaling the number of ASW capable platforms to meet the needs of the future will require more of these talented experts if we continue in the traditional ASW sense,” Darren explained. However, AI and Machine Learning (ML) techniques are being applied in this area to allow Detection, Classification, Localisation and Tracking to be conducted by autonomous maritime platforms, without the need to grow an ASW operator capability. “The edge processing and classification used in swarms of USVs can provide a persistent, resilient distributed network across a wide area,” he added. 

“Availability of sonar data is essential in the training of AI and ML as well as access to the skilled ASW operators to understand the techniques and doctrines used in ASW. SEA is using our own set of recorded raw sonar data to develop an advanced sonar classification tool,” Darren said. “We’ve got lots of marked sonar data, so we can say what data is a track and feed that to an algorithm. It enables the AI/ML to use that data and determine if a contact is a ferry, marine mammal, or something more sinister.” He added that SEA has worked with Mind Foundry in the UK to develop an acoustic track classifier using their Nightingale solution, trained on SEA sonar data. 

This brings a number of benefits, either helping to alleviate the sonar operator’s burden or by complementing their skills. “The operator is bombarded with data and information that places a cognitive burden, limiting how many concurrent contacts that they can analyse. However,  machine learning allows the analysis of multiple contacts, frequencies, and acoustic features across all bearings simultaneously,” Darren told me. 

Tech profile: KraitSense

KraitSense is a miniaturised passive towed array sonar system, with the KraitArray sensor measuring 20 mm in diameter. It has a low drag profile, requiring approximately 10 kg of force to be towed through water, making it suitable for low-power boats and autonomous platforms. The system’s power consumption is low, operating at less than 10 W for a 64-channel configuration. KraitSense can also be deployed statically on a buoy or seabed and can be cross-decked while in service. Its modular design allows for rapid replacement of individual components, with spare modules being portable in a pelicase. 

For processing, it uses a GPU, specifically an NVIDIA Jetson which is compact and can fit in the palm of a hand, replacing traditional chest-high 19-inch racks. The system’s software incorporates machine learning and artificial intelligence, developed in collaboration with Mind Foundry, to automate target classification and reduce the burden on skilled human operators. While primarily a passive sensor, it can function as a receiver in an active sonar system by working with a separate transmitter.

Calibre comment

Russia is definitely competitive and problematic in the sub-surface domain. While some of its capabilities, like the Kilo-class submarine are less of a challenge than they were 30 years ago, others are far more menacing. The Yasen-class is one example, but it is not alone. The Main Directorate of Deep Sea Research (GUGI), a body independent of the Russian Navy that answers directly to the Russian MoD, also represents a significant threat. GUGI operates deep-diving submarines that are capable of operating at extreme depths, where the impact of sabotage would be particularly difficult to repair. Detecting, tracking, and monitoring Russia’s activities below the water’s surface is therefore critical, and a capability that must be recovered. As noted at the outset, NATO cannot build its way out of the ASW gap. The Norwegian and UK procurements of the Type 26 ASW frigate should be evidence enough of this: Together, the two countries have ordered 13 frigates for approximately £18 billion. They are capable ships, doubtless with very effective sensors. But they do not change the reality of the area that must be covered. Autonomous vessels with effective and economical sensors are therefore the only way forward. 

By Sam Cranny-Evans, published on September 19, 2025.