UK and US Make First Torpedo Launch From XV Excalibur Drone to Expand AUKUS Undersea Strike Options.

The UK and US conducted the first heavyweight torpedo launch from an uncrewed underwater vehicle under AUKUS, demonstrating a weapon-release role for XV Excalibur. The trial expands AUKUS undersea experimentation toward armed uncrewed operations and closer integration between the three partners.

XV Excalibur, an experimental extra-large uncrewed underwater vehicle built in Plymouth, carried out the firing in British waters using a heavyweight torpedo developed jointly by the United States and Australia. The test brings together a British underwater platform, a US-Australian weapon, and existing AUKUS interoperability work, showing that an uncrewed system previously used for experimentation and surveillance-related missions can also be configured to carry and release an offensive payload.

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British XV Excalibur XLUUV with Mk 48 heavyweight torpedoes shown in the inset. The weapon fired during the AUKUS trial has not been officially identified, but available information points to the Mk 48 Mod 7 CBASS. (Picture source: Msubs Ltd/ Us DoD)

XV Excalibur is an Extra Large Uncrewed Underwater Vehicle, or XLUUV, developed by MSubs under Project CETUS. The vessel is 12 metres long, displaces about 19 tonnes, and was formally named at Devonport in May 2025. The Royal Navy describes it as a demonstrator intended to test underwater autonomy, bespoke payloads and concepts for operating crewed and uncrewed systems together. It is therefore not an operational combat submarine, but an experimental platform for architectures, interfaces and procedures that could support future systems.

According to an announcement issued by the UK government on 22 September 2026, the firing took place the previous week from XV Excalibur and represented the first joint UK-US torpedo launch from an uncrewed underwater vehicle. London has not identified the exact weapon. However, the available description points to the Mk 48 Mod 7 Common Broadband Advanced Sonar System, or CBASS. Australia’s Defence Science and Technology Group identifies this variant as the product of a bilateral programme with the US Navy. The Mk 48 family is designed to engage submarines and surface ships and combines acoustic homing with the option of wire guidance from the launch platform.

The method used to carry the weapon remains only partly documented. Excalibur does not have conventional torpedo tubes, but it is fitted with a large central payload bay with upper and lower doors. A Mk 48 is around 5.8 metres long, making it too large for the standard central bay. Navy Lookout has assessed that the torpedo may have been carried on a temporary cradle fitted beneath the hull and released before activation. This configuration has not been officially confirmed, but it would be consistent with Excalibur’s experimental role and would avoid major structural modification of the vehicle.

The precise location of the firing has not been disclosed. Excalibur was, however, observed on 16 September at Kyle of Lochalsh in Scotland, close to the British Underwater Test and Evaluation Centre. Operated by QinetiQ on behalf of the UK Ministry of Defence, BUTEC provides real-time three-dimensional tracking of surface vessels, underwater vehicles, weapons and targets. The presence of the XLUUV in the area makes the site a plausible location for the trial, although this has not been confirmed.

XV Excalibur, the Royal Navy’s 12-metre XLUUV developed by MSubs, during sea trials. The platform was later used in the first UK-US heavyweight torpedo firing from an uncrewed underwater vehicle under AUKUS.

The firing follows work carried out in July 2025 during Exercise Talisman Sabre. Under the Maritime Big Play experimentation programme, an operations centre in Australia controlled Excalibur while the vehicle was operating in British waters more than 16,000 kilometres away. That activity focused on command interoperability and the transfer of control of an autonomous system between AUKUS partners. The 2026 torpedo firing adds heavyweight weapon integration to that line of experimentation.

At the tactical and operational level, an armed XLUUV could extend the reach of an undersea force without immediately exposing a crewed submarine. Such a vehicle could operate ahead of a naval group, monitor a chokepoint, contribute to the protection of subsea infrastructure or create an additional attack axis against a surface or underwater target. Several constraints remain central, including detection quality, navigation accuracy, the transfer of targeting data, underwater communications and human authorisation for weapon employment. The trial therefore demonstrates weapon integration and launch from an uncrewed platform, but it does not demonstrate autonomous decision-making for the use of force.

For AUKUS, the test reflects the expansion of cooperation beyond Australia’s nuclear-powered submarine programme. Current work also covers mission architectures, autonomous systems, shared control and common weapon integration. This development is relevant to both the Indo-Pacific and the Euro-Atlantic area, where maritime surveillance and the protection of undersea infrastructure are receiving greater attention. If the three partners standardise command interfaces, payloads, and authorisation procedures, uncrewed vehicles could complement nuclear-powered attack submarines by distributing sensing and strike functions across a broader force structure. Excalibur remains a demonstrator, but the firing indicates the direction of AUKUS work toward more distributed and interoperable undersea operations.

Written By Erwan Halna du Fretay - Defense Analyst, Army Recognition Group
Erwan Halna du Fretay holds a Master’s degree in International Relations and has experience studying conflicts and global arms transfers. His research interests include security and strategic studies, particularly the dynamics of the defense industry, the evolution of military technologies, and the strategic transformation of armed forces.