Breaking News
British Navy Prepares for Deep-Sea Warfare with XV Excalibur Unique Autonomous Submarine in Europe.
On May 15, 2025, the Royal Navy marked a major step in the development of its autonomous underwater capabilities by officially unveiling its first extra-large uncrewed submarine, named XV Excalibur, during a naming ceremony held at HMNB Devonport’s South Yard. Measuring 12 metres in length, 2.2 metres in diameter, and displacing 19 tonnes, this experimental vessel is the largest uncrewed submarine ever tested not only by the Royal Navy but by any European navy to date.
While smaller than conventional submarines, Excalibur offers significantly greater endurance and payload capacity than traditional autonomous underwater vehicles (Picture source: British Royal Navy)
Excalibur is the result of Project CETUS, an experimental programme launched in 2022 and jointly developed by the Royal Navy’s autonomy and innovation teams in collaboration with industry and Defence Equipment and Support (DE&S). The vessel was built by UK-based company MSubs in Plymouth and was first launched in February at Turnchapel Wharf. Since its delivery to the Royal Navy, it has undergone a series of harbour and sea acceptance trials at the Devonport naval base.
The naming ceremony followed naval tradition, with a bottle of Plymouth Gin broken on the hull by Honorary Captain Peaches Golding OBE CStJ RNR, the Lord Lieutenant of Bristol. The name Excalibur pays tribute to a previous British submarine commissioned in 1947, which was used to experiment with high-test peroxide (HTP) propulsion, a concept later abandoned due to the hazards associated with the volatile chemical compounds involved.
The event brought together 200 guests and dignitaries, including Rear Admiral James Parkin, Navy Director Develop, representatives from AUKUS nations, cadets, and recruits from across the Royal Navy. The unveiling represents a tangible step toward the integration of uncrewed underwater systems within British naval forces, at a time when undersea warfare and the protection of critical infrastructure are gaining increasing strategic importance.
Although not intended for operational deployment, Excalibur will be assigned to the newly established Fleet Experimentation Squadron, overseen by the Disruptive Capabilities and Technologies Office. There, it will operate alongside the surface ship XV Patrick Blackett, serving as a testbed for emerging maritime technologies. It will support trials focused on intelligence, surveillance, and reconnaissance (ISR), as well as the use of bespoke sensors or payloads in contested or denied environments.
While smaller than conventional submarines, Excalibur offers significantly greater endurance and payload capacity than traditional autonomous underwater vehicles. Its modular and scalable design is intended to allow adaptation to a wide range of missions, including long-duration surveillance, seabed warfare, sensor deployment, and potentially operations in restricted-access areas.
Rear Admiral Parkin emphasised that the unveiling of XV Excalibur marked a significant moment not only for the Royal Navy and the wider UK Armed Forces, but also for his team, as it signalled the formal handover of the vessel. He underlined the importance of experimentation in the Royal Navy's transition towards greater autonomy and mass, noting that Excalibur would serve as a critical tool in understanding the complexities and operational challenges associated with deploying a future force composed of both crewed and uncrewed underwater systems.
Commodore Marcus Rose, Deputy Director of Underwater Battlespace Capability, explained that the knowledge gained from this programme would build upon the Royal Navy’s previous experience with initiatives such as the Mine Hunting Capability programme. He noted that these insights would help guide the broader integration of uncrewed systems into a combined operational framework. He also highlighted that the successful development and delivery of Excalibur reflected the effectiveness of close cooperation between the Royal Navy and its industrial partners.
By combining technological experimentation, naval heritage, and operational testing, XV Excalibur represents a strategic waypoint in the Royal Navy’s ambition to develop a hybrid fleet of crewed and uncrewed platforms. Its role in evaluating XLUUV capabilities in realistic scenarios will help lay the groundwork for a renewed British doctrine in undersea operations, aimed at maintaining a strategic advantage in increasingly contested maritime environments.