The UK’s first Extra-Large Uncrewed Underwater Vehicle (XLUUV), the 12-metre XV Excalibur, has been formally handed over to the Royal Navy following a landmark year of trials. Developed in under three years by the Submarine Delivery Agency (SDA) in partnership with MSubs Ltd, the 19-tonne vessel is the largest uncrewed underwater vehicle ever trialled by the Royal Navy.
After its official naming at HMNB Devonport in May 2025, Excalibur completed several pioneering demonstrations. During Exercise Talisman Sabre in August, the Royal Navy remotely controlled the vessel from a centre in Australia—over 10,000 miles from its Plymouth homeport. This marked a key AUKUS Pillar 2 achievement, demonstrating trilateral XLUUV interoperability for the first time.
Excalibur also hosted a world-first sea trial, deploying a quantum optical atomic clock developed by UK firm Infleqtion. The “Tiqker” clock enhances navigation accuracy without GPS, enabling submarines to remain submerged and covert for longer periods. The trial was delivered six months ahead of schedule.
Having surpassed its original design specifications during acceptance trials, Excalibur is now under Royal Navy control. The SDA’s Autonomy Unit will continue supporting an extensive two-year test and evaluation programme to explore operational capabilities and integrate autonomy into future service.
These milestones highlight the SDA Autonomy Unit’s rapid innovation in remote and autonomous systems. Excalibur serves as a critical testbed for assessing military payloads and building trust in autonomous operations, paving the way for a future where uncrewed and crewed submarines operate together to enhance the Royal Navy’s underwater advantage.
