The UK Government said on Tuesday that the UK and the US fired a heavyweight torpedo from XV Excalibur, an extra large unmanned underwater vehicle (XLUUV), in UK waters last week.
The trial represented the first time either country had launched a torpedo from an unmanned undersea vessel, rather than a crewed submarine. The US and Australia jointly developed the weapon to engage surface ships and submarines capable of deep dives.
The firing showed that an XLUUV can carry and release a heavyweight weapon. It did not establish an operational capability or indicate that Excalibur selected a target or made an autonomous decision to fire.
Built by Plymouth-based MSubs under the three-year Project Cetus, Excalibur is 12 metres long, two metres across and displaces 19 tonnes. The vessel was formally named at HMNB Devonport in May 2025 and handed over to the Royal Navy later that year.
The Royal Navy has described the XLUUV as a test platform for developing experience with underwater autonomy and modular payloads, while informing future operations involving crewed and uncrewed systems.
Excalibur does not have conventional torpedo tubes. It has a central mission bay designed to accommodate equipment for trials, although the government did not disclose how the torpedo was carried or released during the latest test.
The firing followed an earlier AUKUS experiment involving Excalibur during Exercise Talisman Sabre in July 2025. A remote operations center in Australia controlled the vessel while it operated in UK waters, more than 10,000 miles (16,000 kilometres) from the control team.
The Royal Navy said that exercise tested whether the UK and Australia can operate XLUUVs interchangeably. The latest trial moved the program from remote control and interoperability work into testing a weapons payload.
The Royal Navy has said weapon release from future uncrewed systems will retain human authorisation.
Excalibur is scheduled to continue sea trials as a testbed for payloads and operating concepts and is not scheduled to enter operational service.
