Royal Navy’s first XLUUV is formally named XV Excalibur

The UK Royal Navy (RN) formally unveiled its first Extra-Large Uncrewed Underwater Vehicle (XLUUV) on 15 May 2025 at a ceremony at HMNB Devonport in southwest England.

The experimental vessel, which is 12 m long, has a beam of 2 m and displaces 19 tonnes, was named XV Excalibur. The vessel, which was built by Plymouth-based MSubs and first launched in February 2025, is the largest uncrewed submarine trialled by the RN or any European navy to date.

The XLUUV, which is the culmination of the three-year-long Project Cetus, will carry out extensive sea trials over the next two years, helping to accelerate the RN’s use of advanced unmanned underwater technologies.

Such capabilities are becoming increasingly essential to protect critical underwater infrastructure as well as allied naval vessels and to covertly gather intelligence in the maritime domain.

“The naming of Excalibur is a significant milestone for the Royal Navy and the upcoming sea trials will allow us to rapidly develop our understanding of operating uncrewed vessels of this size underwater,” stated Commodore Marcus Rose, the RN’s deputy director for underwater battlespace capability, at the naming ceremony. “The lessons learnt from this exciting programme will build on our experience from existing programmes, such as the Mine Hunting Capability programme, to inform more extensive use of these technologies in a mixed force of crewed and uncrewed systems.

“Successful delivery of this programme is testament to what can be achieved in collaboration with our industrial partners,” the commodore added.