In a landmark demonstration for allied undersea warfare, the United Kingdom successfully launched an unmodified Mk. 48 Mod 7 heavyweight torpedo from a British XV Excalibur uncrewed submarine on 13 September 2026. The live trial, held at the British Underwater Test & Evaluation Centre in Scotland, marked the first known occasion that a heavyweight torpedo has been fired from an uncrewed vessel.
Background: AUKUS Pillar 2
The trial was part of AUKUS Pillar 2, launched in May 2026 by the United States, Australia and the United Kingdom to develop "cutting-edge payloads and enabling systems for AUKUS partners' Uncrewed Undersea Vehicles (UUVs)." The programme set an initial target delivery window around 2027 and focuses on extending the range, endurance and payload capabilities of partner UUVs.
The Test
The torpedo used was a standard American-made Mk. 48 Mod 7—no special modifications were reported. What made the event notable was the launch platform: the Royal Navy's XV Excalibur, an Extra Large Uncrewed Underwater Vehicle (XLUUV). At more than 39 feet long and roughly 20.9 tons, Excalibur provided the size and payload capacity needed to accommodate the 3,744-lb, 21-inch-diameter, ~19-foot Mk. 48.
U.S. Navy/Wikimedia Commons
"The successful test 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." — Navy press release
Technical Notes
Unlike conventional submarines, Excalibur does not use standard torpedo tubes. Instead, it employs a large central payload bay. Observers suggest the Mk. 48 was likely secured in a cradle along the vehicle's keel for the launch. The test demonstrated smooth integration between the torpedo and the UUV's systems, highlighting mechanical, electrical and software interoperability between AUKUS partners.
Implications and Next Steps
While the live firing proves technical feasibility and allied weapon interchangeability, the Royal Navy emphasizes that Excalibur is an experimental platform used for trials and demonstrations. The successful launch does not mean an immediate decision to field fleets of armed XLUUVs; further testing, evaluations and policy decisions are required before any operational procurement or deployment plans are made.
Still, the trial underscores the potential for modular, interoperable armaments on future uncrewed undersea platforms and advances AUKUS Pillar 2's goal of enabling rapid integration of allied payloads across partner UUVs.
