A Royal Navy deep sea drone has fired a torpedo for the first time in a major technological breakthrough.
The 40ft-long Excalibur crew-less vessel launched a US warhead in secret trials, copying the capability of more expensive and much larger manned submarines.
The UK-built and battery operated subsurface craft has been in trials since 2025 and though it remains an experimental vessel, in future it could offer vital support to the Navy's ageing and overworked fleet of nuclear-powered hunter-killer submarines.
As the Mail has previously revealed, there have been times this year when not a single Astute submarine has been on active service due to maintenance issues and crew rotations.
While working submarines have been conducting the longest patrols in Royal Navy history – in excess of 200 days – to cover for the broken down boats. Those exhausted submarines have returned to port with their hulls covered in barnacles from resting on the seabed for lengthy periods.
While precise details remain classified, the 19-ton Excalibur can dive deeper than larger, manned submarines and can sail from the UK deep into the North Atlantic on a single battery charge. So the addition to the fleet of Excalibur, or a crew-less submarine based on its design, cannot come soon enough, according to naval insiders. Excalibur is also the largest 'drone-sub' ever trialled by the Royal Navy.
Excalibur entered the trials phase of its development in May last year - a development marked by a ceremony at His Majesty's Naval Base (HMNB) Devonport
The Royal Navy's remaining fleet of manned submarines have been overwhelmed by a surge in Russian subsurface activity in the North Atlantic.
Discussing last week's successful trial, a Downing Street spokesman last night described 'a major advance in the future of submarine technology'.
The breakthrough will be discussed by UK Prime Minister Andy Burnham and US President Donald Trump in talks in New York this week.
How many Excalibur-type submarines will be operational this decade has not been disclosed but their development is a major boost for UK security including addressing the issue of the strategically vital network of communication and energy cables on the sea bed.
Those cables have been surveyed by Russian spy ships and submarines and would be vulnerable to attack in a time of warfare. Excalibur could monitor the pipelines.
The torpedoes, designed as part of the AUKUS submarine programme involving the UK, US and Australia, can target enemy surface and sub-surface vessels.
Excalibur was designed by maritime engineering company MSubs in Plymouth, Devon, as part of a £6million development contract – a tiny sum in naval engineering. Initially the crew-less submarine was designed to carry payloads of equipment thereby creating more breathing space aboard the Royal Navy's manned hunter-killer and bomber vessels.
Excalibur belongs to the Royal Navy's Fleet Experimentation Squadron.
Over the next two years, Excalibur will carry out further sea trials, helping to accelerate the Royal Navy's use of advanced technologies.
It will help develop a better understanding of the unique challenges that come with operating uncrewed vessels of this size – with the aim of future vessels working alongside crewed platforms.
The trials and testing will contribute significantly to the Royal Navy's constant efforts to remain ahead of potential foes beneath the waves, safeguarding key infrastructure, protecting British and allied ships and submarines and gathering intelligence.