The Royal Navy has completed a six-week trial with the US and Royal Australian Navies to demonstrate how uncrewed underwater technology can protect critical undersea infrastructure (CUI), split between the US east and west coasts and waters off southwestern Australia.

Exercise Lanternfish, the latest collaborative trial under the AUKUS Pillar 2 agreement, saw Royal Navy divers and hydrographic experts operate alongside their American and Australian counterparts. The Diving and Threat Exploitation Group deployed its VideoRay Defender, a small remotely operated submersible used to locate mines and underwater explosive devices, while the Devonport-based Hydrographic eXploitation Group launched its Teledyne Gavia autonomous underwater system, a modular platform that can be reconfigured for different missions depending on its sensor fit.

The systems were used to survey critical undersea infrastructure and rehearse responses to potential hostile activity, operating as part of a wider network of sensors and underwater vehicles to build a fuller picture of the subsea environment. The exercise aimed to improve how the three nations detect, monitor and respond to undersea threats, and to develop common operating procedures between them.

Undersea infrastructure, including subsea power cables, internet cables and pipelines, has become an increasingly prominent security concern for Western navies, since much of it sits in international waters where monitoring and attribution are difficult, and where a single act of sabotage can disrupt communications or energy supply across an entire region. Exercises like Lanternfish are, in part, a response to this growing awareness, testing not just the hardware but the procedures needed to identify and react to interference quickly.

Lt Cdr Mark Wilton, from the Hydrographic eXploitation Group, said the Seabed Warfare team had worked closely with AUKUS partners, including using Royal Australian Navy equipment directly, and completed a range of Gavia missions covering acoustic calibration, night-time operations and independent, unaided runs.

The trial comes amid rising concern over threats to undersea infrastructure from foreign state actors, including a covert Russian submarine operation in and around UK waters reported earlier this year. AUKUS Pillar 2 focuses on the collaborative, accelerated deployment of advanced military capabilities across the UK, US and Australia, distinct from Pillar 1, which covers the transfer of nuclear-powered submarine capability to Australia.

Commodore Marcus Rose, Deputy Director Defence Underwater, said the exercise offered a valuable opportunity to test interoperability in a real-world setting and refine capabilities at pace. Lanternfish also reflects the Royal Navy's broader shift toward a Hybrid Navy model, in which crewed and uncrewed capabilities operate together, with uncrewed systems increasingly taking on the more repetitive, dangerous or time-consuming elements of underwater survey and threat response, freeing personnel for tasks that require direct human judgement.

For naval architects and systems designers, the exercise underlines a continuing shift in procurement priorities, with modular, reconfigurable platforms like the Gavia increasingly valued over single-purpose systems, since they can be adapted across missions without a full redesign.

Planning is already underway for the next AUKUS Pillar 2 operational exercise, which will extend allied integration testing across the maritime, air, cyber and space domains.