US, UK Navies Launch Mk 48 Torpedo From British Uncrewed Submarine

The launch took place on September 13, 2026, at the British Underwater Test & Evaluation Centre in Scotland under Project Broadsword, which had been approved only seven months earlier, according to TechRadar. The test examined whether an American weapon could be integrated with a British autonomous underwater vessel through compatible mechanical, electrical and software systems.

Project Broadsword sits within AUKUS Pillar II, the technology-focused part of the security partnership between Australia, the United Kingdom and the United States. AUKUS Pillar II covers cooperation on advanced capabilities including artificial intelligence, autonomy, quantum technologies and advanced undersea systems. Approved in February 2026, Broadsword brought together the Department of the Navy Rapid Capabilities Office, OPNAV N97, the Royal Navy, the Defense Innovation Unit, Naval Undersea Warfare Center Keyport and industry partners.

The project connected the Mk 48 with XV Excalibur, an extra-large uncrewed underwater vessel designed for autonomous or remotely controlled operations. Unlike a conventional attack submarine, Excalibur does not have traditional internal torpedo tubes, so engineers mounted the approximately 3,700-pound weapon externally beneath its hull. That configuration allowed the teams to conduct the launch while testing the interfaces required between the American torpedo and the British underwater platform.

Excalibur had already been used by the Royal Navy as a mobile underwater laboratory for testing technologies and future payloads. In 2025, the vessel was remotely controlled in British waters from a command centre in Australia, approximately 10,000 miles away. Those tests gave the Royal Navy experience operating an uncrewed underwater platform without placing personnel aboard the vessel during its missions.

Adm. Daryl Caudle, Chief of Naval Operations, said the test marked a historic first for allied undersea warfare. “This successful test marks a historic first for allied undersea warfare…validates our shared vision for true interchangeability,” Caudle said. “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 test showed that a U.S. weapon could be integrated with a British uncrewed platform rather than requiring both systems to be developed exclusively around individual systems. Vice Adm. Robert Gaucher, Director of Submarine Programs, described the launch as an important early step toward developing greater interoperability for autonomous undersea systems.

The U.S. Navy plans to continue the work through Project CUTLASS, using Anduril's Dive-XL platform for the next stage of development. The follow-on effort will examine payload integration, command and control systems, and operational scenarios involving uncrewed underwater platforms. The Navy said this work will further develop the use of autonomous underwater vessels with different payloads and mission systems.

The September launch completed the Broadsword proof-of-concept, while CUTLASS now moves the effort toward additional integration and operational testing. Further trials will determine whether the approach can support other weapons, platforms and mission configurations beyond the system used during Broadsword.