The Royal Navy successfully launched a U.S. Navy Mk 48 Heavyweight Torpedo from the British Excalibur uncrewed underwater vehicle, marking a major advance toward allied operational fleets of uncrewed systems beneath the waves.
The Sept. 13 launch occurred at the British Underwater Test & Evaluation Centre in Scotland.
The successful event demonstrated cooperation between the U.S. and Royal Navy on integrating American weapons with a British autonomous underwater platform.
The test represents a significant operational achievement for AUKUS Pillar 2, the multilateral agreement involving the United States, United Kingdom and Australia.
Under the May 2026 agreement, the allies aim to enable uncrewed undersea vehicle payload systems that can be used across each country’s vehicles.
Although the launch remains a proof of concept, the Navy press release said it “validated the mechanical, electrical, and software integration of a U.S. kinetic payload onto an allied autonomous vessel, proving that allied forces can rapidly achieve weapon interchangeability.”
That validation went beyond simply placing an American torpedo on a British platform.
The test addressed the mechanical, electrical and software connections needed to launch the weapon from an allied autonomous vessel.
Adm. Daryl Caudle, Chief of Naval Operations, called the allied cooperation and testing “a historic first for allied undersea warfare.”
He said, “Proving that we can seamlessly launch a U.S. heavyweight torpedo from a Royal Navy autonomous underwater vehicle validates our shared vision for true interchangeability.”
Caudle added, “By integrating weapons, payloads, and mission architectures across allied platforms, we are increasing the flexibility, scale, and combat power of our combined forces and ensuring they are ready to meet the strategic demands of tomorrow.”
The latest Mk 48 version is the MOD 7, which resulted from a Joint Development Program with the Royal Australian Navy.
According to the Navy, the MOD 7 is optimized for both “traditional and emerging missions.”
The Excalibur, unveiled in May 2025, is the Royal Navy’s first uncrewed submarine.
Video from the launch appears to show the Mk 48 positioned beneath the British submersible, which measures nearly 40 feet, and launched from a cradle attached to the vehicle’s hull.
The Mk 48 is the U.S. Navy’s standard heavyweight torpedo.
It measures 19 feet in length and has a diameter of 21 inches, creating a notable integration challenge for the British vehicle.
According to the U.K.’s Navy Lookout, “Excalibur has no torpedo tubes, but a large central payload bay with doors at the top and bottom. However, the Mk 48 torpedo… is too long to fit in the standard central payload bay.”
The cradle arrangement visible in video offered a way to carry and launch the weapon despite the size limitation described by Navy Lookout.
The source reported that the torpedo appeared to be mounted beneath Excalibur rather than placed within its central payload bay.
Close coordination between the two navies could make it conceivable for future uncrewed underwater vehicles to employ sophisticated weapon launch arrangements suitable for both British and American technologies.
The successful heavyweight torpedo deployment is described as only the first step under AUKUS Pillar 2.
The United States and Royal Navy are continuing what the release called an aggressive “follow-on acceleration with Project CUTLASS.” That project will use the Anduril Dive-XL platform as the allies push the effort beyond this initial demonstration.
According to the release, Project CUTLASS will address “advanced payload integration data, command and control architectures, and tactical employment scenarios to further mature uncrewed undersea capabilities.”
The work follows the successful proof of concept with Excalibur and the U.S. Mk 48.
The Scotland launch therefore established that an American heavyweight torpedo could be integrated with and fired from a British autonomous underwater vessel.
For the three AUKUS partners, the result provides a concrete demonstration of the weapon interchangeability envisioned under Pillar 2.
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