BRITISH naval innovation has reached a major new milestone after the Royal Navy successfully fired a heavyweight torpedo from an uncrewed submarine for the first time.
The historic trial took place in Scottish waters using XV Excalibur, a 12-metre Extra-Large Uncrewed Underwater Vessel, or XLUUV, developed as an experimental platform for the Royal Navy.
Excalibur was adapted with a specialist system enabling it to launch and control a US Navy Mk48 Mod 4 heavyweight torpedo at the British Underwater Test and Evaluation Centre, known as BUTEC, near Kyle of Lochalsh on Scotland’s north-west coast.
The Royal Navy said the three-week experiment used an inert, recoverable version of the torpedo, allowing the weapon and its integration with the vessel to be tested without an explosive warhead.
It marks the first time the Royal Navy has successfully fired a torpedo from one of its uncrewed submarines and, according to the Government, the first time either Britain or the United States has launched a heavyweight torpedo from an uncrewed underwater vessel rather than a crewed submarine.
The achievement is particularly significant for British defence technology, with Excalibur built in Plymouth and now being used as a testbed to accelerate the Royal Navy’s development of autonomous and uncrewed underwater systems.
The trial, codenamed Project Broadsword/Trial Iron, was carried out by the Royal Navy alongside the United States Navy, the UK’s Submarine Delivery Group Autonomy Unit and industry partners MSubs and QinetiQ.
Remarkably, the project was brought together in just six months.
The Mk48 is a formidable heavyweight torpedo, measuring almost six metres in length and weighing more than one-and-a-half tonnes. Operational versions are designed for use against submarines and surface warships.
Neither Excalibur nor the Mk48 had originally been designed to operate together, making the successful integration an important demonstration of how existing technology can potentially be adapted rapidly rather than requiring entirely new vessels and systems to be designed from scratch.
The experiment forms part of AUKUS, the defence partnership between Britain, the United States and Australia.
Under AUKUS Pillar II, the three countries are working together on advanced military capabilities including artificial intelligence, autonomy, quantum technologies and undersea warfare.
Earlier this year, the three nations announced their first AUKUS Pillar II “signature project”, concentrating on payloads and enabling systems for uncrewed underwater vessels, with delivery due to begin in 2027. The Ministry of Defence says the programme is intended to allow such vessels to undertake roles including surveillance, protection of critical seabed infrastructure and support for anti-submarine and anti-surface warfare.
Excalibur itself entered Royal Navy service as an experimental vessel in May 2025 and is being used to investigate how large autonomous submarines could operate alongside Britain’s traditional crewed warships and submarines.
The British-built vessel has already demonstrated some extraordinary capabilities.
During Exercise Talisman Sabre, the Royal Navy successfully controlled Excalibur operating in British waters from a remote operations centre in Australia, more than 10,000 miles away. It has also taken part in a world-first sea trial involving an advanced quantum optical atomic clock.
The latest torpedo trial represents another step towards the Royal Navy’s proposed “Hybrid Navy”, in which sailors, ships and submarines operate alongside increasingly sophisticated autonomous and uncrewed platforms.
First Sea Lord General Sir Gwyn Jenkins said the trials represented a “pivotal moment” for AUKUS and demonstrated what Britain, America and Australia could achieve by working together.
He said the work showed how uncrewed vessels operating alongside conventional warships and submarines could provide greater combat power beneath the waves while reducing risks to personnel.
Lieutenant Commander David Iwanek, the UK trial director, said the importance of the achievement “cannot be overstated”, describing it as paving the way for a major change in underwater capability.
Further trials are expected to increase in scope and complexity as the allies investigate the possibility of eventually deploying torpedo-carrying uncrewed underwater vessels on operations.
For Britain, the breakthrough is another demonstration of the country’s long tradition of maritime engineering and naval innovation, this time combining British expertise, a Plymouth-built experimental submarine and close cooperation with two of the UK’s most important defence partners.
More than a century after the Royal Navy helped pioneer submarine warfare, British engineers and sailors are once again helping to shape what warfare beneath the waves could look like in the decades ahead.
Image: MOD Crown Copyright News / Editorial Licence.
