UK's Submarine Delivery Agency hands Excalibur XLUUV over to Royal Navy

XV Excalibur (MSubs Cetus XLUUV) during launch in March 2025. Image provided by Brett Phaneuf, MSubs, via email on 5 June 2025 for use in Janes reference publications. (MSubs)

The UK Ministry of Defence's (MoD's) Submarine Delivery Agency (SDA) handed over the extra-large unmanned underwater vehicle (XLUUV) Excalibur to the Royal Navy (RN) in December 2025.

Also termed an autonomous submarine by the MoD, the 12 m, 19 tonne Excalibur is the largest UUV ever trialled by the RN. It was named and unveiled at a ceremony in His Majesty's Naval Base (HMNB) Devonport in May 2025.

At Exercise ‘Talisman Sabre', in August 2025, RN operators successfully controlled Excalibur in UK waters from a remote operating centre in Australia – more than 16,000 km from its base in Plymouth. The exercise marked the first time the UK and Australia have demonstrated XLUUV interoperability as a single fighting force, seen by the MoD as progress in the second part of the Australia-UK-US defence partnership known as AUKUS Pillar 2.

The handover is the culmination of Project Cetus, with Excalibur under development since 2022 with the SDA in partnership with UK-based manufacturer MSubs Ltd. The RN intended for Project Cetus to build trust in naval autonomy and to be a testbed to assess military payloads and missions.

Excalibur has already completed various acceptance trials, with the MoD saying on 11 December that those included “surpassing several original design specifications”.

Excalibur will now undergo extensive sea trials until 2027, with the SDA's Autonomy Unit continuing to support the RN on Excalibur's test and evaluation programme.

For more information, please see MSubs launches Cetus XLUUV technology demonstratorandFeature: UK's Project Cabot looks to exploit AI and digitalisation to build ‘Atlantic Bastion' .