UK Royal Navy unmanned submarine fires heavyweight torpedo during trial

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.