Royal Navy says it led anti-submarine scenarios as NATO REPMUS exercise tested uncrewed systems

The Royal Navy said on 1 October 2026 that, with the UK's focus on anti-submarine warfare (ASW), it acted as "the lead for the operational scenarios and trials" at Exercise REPMUS, the annual autonomous wargame that the Navy describes as a NATO exercise, hosted this year by the Portuguese Navy at Troia. In its account the UK was testing uncrewed and autonomous equipment it says will inform the Royal Navy's Atlantic Bastion programme.

This piece rests on the Royal Navy's own news release. It is a Ministry of Defence account of its own part in the exercise: it names no companies, and it gives no detection rates, test results or other performance figures.

Who took part

• The Royal Navy says it "sent around 200 people, including sailors, scientific support staff and industry, to Troia", where it was "leading an international contingent from ten NATO and partner nations".
• The release says the exercise "was supported by five support ships from Germany, France, the Netherlands and NATO’s Centre for Maritime Research and Experimentation".
• It says Sweden "deployed fixed wing airborne drones for intelligence, surveillance and reconnaissance missions", and that Portugal "also flew drones which drop sonobuoys and relay the data back to a command centre ashore".

According to the Navy, participants "were looking to develop their ASW capabilities and their ability to conduct surveillance of underwater infrastructure".

What was tested

The release describes three strands of equipment:

• Underwater gliders. The release says: "Several types of underwater gliders were deployed from those feeding back real-time assessments of the oceanography to larger sentinel gliders using long acoustic vertical arrays to detect and track potential threats."
• Squads of uncrewed surface vessels. "Squads of small and medium uncrewed surface vessels were used to gather acoustic data and provide real time contact reports of submarine targets". The Navy calls this "a proof of concept for larger squads and versions of such vessels".
• Two larger autonomous boats. It says "two autonomous boats – one 12, the other 17 metres long – were tested to tow sonar systems, drop automated sonobuoys (underwater microphones) for detecting submarines and the launching of gliders."

The release says what the systems were tested to do. It does not say how well they did it.

Not yet adopted

The Royal Navy is explicit that this was evaluation, not procurement. It says the exercise let it "sponsor UK industry to allow the evaluation of potential technologies in an international context, not yet formally adopted by the RN but which will inform future options adopted under Atlantic Bastion."

Autonomy, and where AI comes in

The REPMUS release describes the equipment as uncrewed and autonomous. We read it in full, and it does not mention artificial intelligence or machine learning, so we do not describe these trials as AI.

AI does appear in the official description of the wider programme. When the Ministry of Defence unveiled Atlantic Bastion on 8 December 2025, its gov.uk release said the programme "will combine autonomous vessels and AI with warships and aircraft", and that it "will see ships, submarines, aircraft and unmanned vessels connected through AI-powered acoustic detection technology and integrated into a digital targeting web". That is the MoD's account of what the programme is meant to become, not of what was shown at Troia.

Atlantic Bastion, in the government's words

The 1 October release describes Atlantic Bastion as "the use of hybrid forces to defend the UK and NATO allies against evolving threats". The December 2025 gov.uk release said it is "in direct response to a resurgence in Russian submarine and underwater activity", and that "combined MOD/industry seedcorn investment of £14 million" had been "committed this year to testing and development". It said "26 firms from the UK and Europe have submitted proposals to develop anti-submarine sensor technology", with "capabilities due to be deployed in the water next year" (that is, 2026, as the Royal Navy's version of the same announcement puts it).

The Navy says its participation in REPMUS comes as it continues "its shift to a hybrid navy – one that sees autonomous and uncrewed systems integrated to work alongside traditional ships and aircraft." The UK's head of delegation, Cdr (Rtd) Ian Danbury OBE, said it was a privilege to lead the team, according to the release, which reports his remarks rather than quoting them directly.

Uncrewed boats have featured on these pages recently: in September we covered a Portsmouth demonstration in which, Shield AI and Kraken said, Shield AI's software coordinated two Kraken uncrewed boats; their announcement named no Royal Navy role.

Why it matters

On our reading, the release is a status report from the Navy rather than evidence of capability. It shows the kinds of uncrewed anti-submarine tools the Royal Navy says it is evaluating with allies, including boats that tow sonar and drop sonobuoys, and it says the industry technologies it sponsored there are not yet formally adopted. What it does not show is whether any of them worked well enough to be bought; the Navy says only that they "will inform future options" under Atlantic Bastion.