Royal Navy receives autonomous submarine XV Excalibur following completion of acceptance trials

Officially classified as an Extra-Large Uncrewed Underwater Vehicle, Excalibur is a 12-metre experimental submarine with a displacement of 19 tonnes, making it the largest of its kind ever trialled by the Royal Navy. The vessel is the culmination of Project Cetus and was developed in under three years by the Submarine Delivery Agency in partnership with MSubs Ltd.

Excalibur was named and unveiled in May 2025 at a ceremony held at His Majesty’s Naval Base Devonport and is scheduled to undertake two years of extensive sea trials. These trials are designed to assess the opportunities and challenges associated with operating an uncrewed submarine of this size.

The vessel has already demonstrated long-distance interoperability during Exercise Talisman Sabre, when it was successfully controlled in UK waters from a remote operating centre in Australia, more than 10,000 miles away. As part of AUKUS Pillar 2, the exercise marked the first time the UK and Australia demonstrated Extra-Large Uncrewed Underwater Vehicle interoperability as a single fighting force.

Excalibur has also taken part in a world-first sea trial carrying a quantum optical atomic “Tiqker” clock developed by Infleqtion, marking the first operation of such a device at sea in an underwater vessel. Since launching in February 2025, the submarine has surpassed several original design specifications, and the SDA’s Autonomy Unit will continue to support the Royal Navy as Excalibur progresses through its test and evaluation programme.

Source: Submarine Delivery Agency.