The U.S. Navy and Royal Navy successfully launched a U.S. Mk 48 Heavyweight Torpedo from a British Excalibur uncrewed underwater vehicle (UUV) on Sept. 13 at the British Underwater Test & Evaluation Centre in Scotland, marking a first-of-its-kind test for both countries.
The proof-of-concept launch, announced Sept. 22, was conducted under AUKUS Pillar 2, the trilateral agreement between the U.S., U.K., and Australia to enable UUV payload systems usable across each country’s vehicles, according to a May 2026 agreement. Personnel from the Pentagon’s Defense Innovation Unit and the Naval Undersea Warfare Center Keyport Division, along with industry partners, took part in the test.
The exercise torpedo was slung under the nearly 40-foot-long, 19-metric-ton Excalibur UUV, which was unveiled in May 2025 as the Royal Navy’s first uncrewed submarine. The Mk 48, the U.S. Navy’s standard heavyweight torpedo, is 19 feet long with a 21-inch diameter. According to Navy Lookout, the Excalibur has no torpedo tubes but a large central payload bay; the Mk 48 is too long to fit in that bay, so the weapon was launched from a cradle attached to the hull.
The external torpedo launch capability was developed under two efforts called Project Broadsword and Trial Iron, according to a U.S. Navy press release. The project was approved in February 2026 by the Department of the Navy Rapid Capabilities Office and executed in less than seven months.
The 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,” the Navy said.
“This successful test marks a historic first for allied undersea warfare,” said Adm. Daryl Caudle, Chief of Naval Operations. “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.”
U.S. Navy Vice Adm. Robert Gaucher, Director of Submarine Programs, called the demonstration “an important early step in developing lethality in our undersea autonomous systems.” U.K. Minister of State for Defence Readiness and Industry Luke Pollard said the test is “a really important moment in our journey towards building a hybrid navy,” where crewed ships and submarines operate alongside uncrewed vessels, and “a substantial increase in our lethality.”
The U.S. and Royal Navy continue work under AUKUS Pillar 2 to develop weapon launch arrangements suitable for both British and American technologies.
Sources: Defense News · Defense News