The Royal Navy has successfully tested Excalibur, a 40-foot unmanned submarine, firing a torpedo for the first time in a significant technological achievement. This breakthrough is crucial because the Navy's manned submarine fleet is severely overextended, with instances where no Astute-class submarines were operational due to maintenance, forcing remaining vessels to conduct record-breaking patrols exceeding 200 days. The addition of crewless submarines like Excalibur could provide vital relief to this ageing and exhausted fleet whilst maintaining operational capability against increased Russian submarine activity in the North Atlantic.

Excalibur, a 19-ton battery-powered vessel designed by Plymouth-based maritime engineering company MSubs at a cost of £6 million, can dive deeper than larger manned submarines and travel from the UK to the North Atlantic on a single charge. The submarine, which entered trials in May 2025 as the largest drone-sub ever tested by the Royal Navy, is equipped with AUKUS programme torpedoes capable of targeting surface and subsurface vessels. Beyond offensive capability, Excalibur could monitor strategically vital undersea communication and energy cables that have been surveyed by Russian spy ships, representing an additional security benefit. Further sea trials are planned over the next two years, with the technology being presented to UK Prime Minister Andy Burnham and US President Donald Trump during talks in New York.