Unmanned submarine “XV Excalibur”: Royal Navy fires Mk48 heavyweight torpedo for the first time

An unmanned submarine of the Royal Navy has fired a heavyweight torpedo for the first time: off the Scottish coast, the twelve-metre “XV Excalibur” launched a Mk48 Mod 4. For armed unmanned underwater vehicles, the trial marks an important step.

The setting was the British Underwater Test and Evaluation Centre (BUTEC) near Kyle of Lochalsh. The “XV Excalibur”, an experimental Extra-Large Uncrewed Underwater Vessel (XLUUV), had previously been fitted with a special system that controls and releases the US-built Mk48 Mod 4. The round fired was an inert torpedo variant that can be reused.

Also remarkable is how quickly it happened: British and US teams, together with industry partners, needed just six months to integrate and trial the capability.

AUKUS pillar two: the path to an armed XLUUV

“Project Broadsword/Trial Iron” is the name of the trial. It runs under the second pillar of AUKUS, the agreement between Australia, the United Kingdom and the United States; this pillar aims to develop new military capabilities rapidly. The current test opens a series of trials of gradually increasing complexity. The end goal is unmanned underwater vehicles that take on armed missions – without putting a crew in danger.

These trials mark a pivotal moment for AUKUS and show what the United Kingdom, Australia and the United States can achieve together— First Sea Lord General Sir Gwyn Jenkins

The “XV Excalibur”, Jenkins continued, shows how unmanned systems could in future deliver “greater combat power under water” side by side with crewed warships and submarines.

On the torpedo: the Mk48 measures just under six metres and weighs more than 1.5 tonnes. Designed as a heavyweight torpedo against submarines as well as surface ships, it is in service with several navies. The fact that neither – torpedo nor “XV Excalibur” – was ever designed to work with the other makes the combination a demonstrator: existing systems can be brought together quickly, without first having to develop specialised platforms in a lengthy process.

Unmanned submarine as test platform for the “Hybrid Navy”

The “XV Excalibur” was built by the company MSubs and has been in service since May 2025. The Royal Navy uses the twelve-metre experimental submarine to trial new technologies in the fields of autonomy and unmanned systems. Behind this lies the British “Hybrid Navy” concept: in future, conventional warships and submarines are to operate closely with autonomous and unmanned systems – the trial is part of this concept.

Lieutenant Commander David Iwanek, who led the tests on the British side, also spoke of an important step:

The significance of this success can hardly be overstated – it paves the way for a fundamental leap in underwater strike capability.— Lieutenant Commander David Iwanek, British test lead