Project CABOT, transforming ASW for the Royal Navy

Project CABOT is the UK MoD’s plan to address its ASW gap and urgent need for additional sensors using a bold strategy and partnership with industry. This article looks at what the Project aims to achieve, as well as some of the companies that could be positioned to meet its requirements. 

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. 

Now, the Royal Navy and Marines maintain a total regular strength of 32,150, just marginally higher than the RAF at 30,450, according to government reporting from Q1 of 2025. Outside of support vessels and the Fleet Auxiliary, the Navy has six destroyers, ten general purpose frigates (several of which are due to be decommissioned), two aircraft carriers, six nuclear attack submarines (with one more on the way) and four submarines upholding its nuclear deterrent for a total of 17 surface vessels and 10 submarines at its disposal. First Sea Lord Admiral Sir Ben Key said that around 50% of the fleet was either at very high readiness or operationally deployed at any given time. It is clear that the Royal Navy has shrunk significantly from its Cold War status and despite the planned procurement of the Type 26 and Type 31 (eight and five ships respectively), its strength is not set to increase meaningfully . Indeed, the total fleet will number around 21 surface vessels and 11 submarines in the mid-2030s, assuming that none of the proposed 12 SSN-AUKUS submarines have been commissioned by that point. 

So what? Armed forces are shrinking – a  trend that has been clear for some time – since Soviet submarines were last regarded as a major threat, in fact. The challenge for the Royal Navy is that it must once more get to grips with Russian submarines seeking to push through the Greenland, Iceland, UK (GIUK) Gap – starting with the vast expanse of the Norwegian and Greenland seas mentioned above. There are currently five Yasen-M class submarines, with four more planned or under construction in the Russian fleet. A small portion of the total – an  estimated 64 submarines, including the nuclear missile-armed Borei class, which forms an important element of the Russian nuclear deterrent, in part because of its survivability. Altogether, this means the Royal Navy must be able to track a potent threat over a large area with fewer assets and personnel than it has ever had before. Fortunately, the number of submarines Russia has at its disposal is much lower than during the late Cold War, but there is very little substitute for lots of platforms and sensors in ASW. Here, the Navy has a plan, designated Project CABOT, which aims to help address the need for ASW assets at scale. 

Phase 1: Atlantic Net

Project CABOT builds upon Project CHARYBDIS and the ASW Barrier Smart Defence Initiative, a NATO effort led by the UK. CABOT is broken down into two phases with the ultimate goal of delivering a “portfolio of lean-crewed, remote-operated, and uncrewed/autonomous airborne, surface and subsurface vehicles, sensors and nodes to provide a deployable and persistent wide area ASW search capability,” according to the initial market engagement launched in February 2025. Documents pertinent to that announcement clarified the plan to some extent, which remains dependent upon MoD investment decisions. 

Phase 1 is referred to as Atlantic Net and envisages a contractor-owned, contractor-operated model, with autonomous platforms carrying acoustic sensors deployed across the GIUK gap. The data collected by those sensors would be triaged by artificial intelligence and fed to remote operations centres staffed by the Royal Navy. The requirements for Atlantic Net were expected to be set by the end of 2025, with the data strategy formulated out to the end of 2026 and systems deployed from the beginning of that year. The contractor-owned model is then scheduled to continue out to 2029, when a decision will be made on whether to scale or iterate the programme, or transition it to phase two, known as Bastion Atlantic. 

The Prior Information Notice, which indicates the MoD is moving the project ahead to some extent, was announced in May 2025 and valued at up to £20 million. Covering a period of 4.5 years, it focused on the contractor-owned portion of the programme. 

There are several potential players in this field, and Helsing’s prominent launch of Lura and SG-1 Fathom in May 2025 is likely positioned for the requirement. The SG-1 Fathom is the company’s autonomous glider developed in partnership with Blue Ocean Marine Tech Systems, Ocean Infinity, and Qinetiq. It is designed to be deployed for three months before being recovered and recharged to be deployed again. It is a completely passive system whilst underwater and fitted with passive sonar and a small powerful computer from NVIDIA called a Jetson, which runs a foundational AI model called Lura. A foundational model simply means that the algorithms have been trained on a range of acoustic data enabling them to detect and understand things in the operational world they might not have encountered during training. When a threat signal is identified, the SG-1 Fathom returns to the surface and transmits signals via satellite links before continuing with its patrol. Helsing indicated that hundreds of SG-1s could be deployed to continuously monitor a given area. 

Helsing is not alone, however, with Anduril having revealed its Seabed Sentry in April 2025. The system is designed to operate on the seabed with the sensors networked – allowing data to be shared between each sensor – providing persistent and autonomous situational awareness on the seafloor, the company states. It uses acoustic communications links to transmit data between the nodes, which suggests a fairly limited bandwidth and range, and a passive Sea Spear sonar from Ultra Maritime is carried. Like the SG-1 Fathom, Seabed Sentry is completed by edge AI, designed to make sense of the gathered data as it is collected. 

Other competitors might include the UK’s Kraken Technologies, which produces a range of uncrewed surface vessels as well as the Manta family of all-electric surface/sub-surface vessels, which can carry up to 5,000 kg in the K4 Manta 54 configuration, travel at 60 knots, and patrol for up to 30 days. More recently, SEA has discussed its KraitSense towed array and a partnership with ACUA that will see the system deployed from a USV. During REPMUS 2025, Zero USV and its Oceanus12 USV autonomously deployed a fibre-optic towed array from Optics11. Furthermore, as Project CABOT is badged as a component of NATO’s Digital Ocean initiative, the Allied Underwater Battlespace Mission Network project (AUWB-MN) may come to shape its future direction. AUWB-MN “will exploit both acoustic communication and more novel techniques to provide:

• Reliable underwater communications
• Interfaces to above-water terrestrial and satellite communications utilizing radio frequencies and other innovative communication bearers
• Effective command and control delivery
• And the conduit for data-harvesting, data fusion and data exploitation.”

The UK has several companies in the autonomy space that could provide solutions to Phase 1 of Project CABOT. It is probable that the potential contribution to the British economy, as well as the company’s understanding of the customer requirements, will be key to success in this competition. 

Phase 2: Bastion Atlantic 

Bastion Atlantic is set to be enacted throughout the Atlantic Net project, which suggests that getting something into the water soon is seen as a priority. The Royal Navy has reportedly indicated that the Atlantic Net is intended to free up traditional naval assets for other tasking, and it is expected to significantly increase mass and persistence at sea. This may be a reflection of the platform and personnel limits mentioned above. 

Ultimately, Bastion Atlantic will transition the project to a government-owned, government-operated model, which will constitute a large mixture of sensors and platforms. The Navy’s presentation, released with the market engagement, indicated the Type 92 USV and Type 93 extra large unmanned underwater vessels would be involved, as well as the Type 26 and Astute-class submarines. Of course, a range of airborne platforms will further complement the ASW capabilities available to the Navy, with the RAF’s P-8A Poseidons standing as key elements in wide area surveillance. The whole project is expected to have transitioned to the government-owned model by 2030, which suggests an aggressive timeline that may be difficult to meet, given the early stage development of many of the capabilities that it seeks to exploit. 

Both phases of the project contribute to the UK’s nuclear deterrent by resourcing and supporting the role traditionally performed by the Towed Array Patrol Ship (TAPS). The role has been performed by Type 23s with Type 2087 Towed Array Sonars, maintaining a constant watch throughout UK waters, the North Atlantic and Norwegian Sea looking for Russian submarines. This helps to protect the nuclear submarine fleet and keep Russian submarines away from British shores. However, with the gradual retirement of much of the Type 23 fleet and introduction of the Type 26, there is growing strain on the ability to maintain the TAPS  capability, as well as an increased need to be more effective in performing the role. The sensor fusion and greater area covered by Project CABOT should, therefore, contribute meaningfully to this vital capability. 

Calibre comment

Like the British Army, the Royal Navy is necessarily pursuing a mix of crewed and uncrewed capabilities to meet the demands placed upon it. It is clear that increasing the numbers of personnel and ships to meet the ASW demand conventionally is unlikely to succeed. Even doubling the number of Type 26s to 16 would not necessarily solve the ASW gap. So, it stands to reason that a hybrid approach is the most suitable way to ensure the Royal Navy can find and track Russian submarines. There are, however, many technological and doctrinal hurdles to be overcome between where the Navy is now and where it wants to be. 

By Sam Cranny-Evans, published on September 25, 2025. The lead image shows an RAF Poseidon on a training flight off the coast of Scotland. The Poseidon fleet is equipped to track and engage submarines using Mk 54 torpedoes. Credit: Cpl Adam Fletcher/UK MOD © Crown copyright 2021.