UK Awards $8.8M Contract for 21-Tonne XLUUV XV Excalibur to Begin Autonomous Deep-Dive and Payload Trials

UK's CETUS Programme Secures New Contract to Drive Real-Sea Trials of Giant UUV

The UK's Submarine Delivery Agency (SDA) has awarded an $8.8 million contract to Plymouth-based MSubs under the Procurement Act 2023, formally launching a trials programme for the Extra-Large Uncrewed Underwater Vehicle (XLUUV) XV Excalibur. The programme aims to validate the vessel's autonomous underwater operations and payload integration capabilities.

MSubs will conduct the trials at its Plymouth facility and in nearby waters, with work expected to continue through 2028. As the sole developer of the CETUS programme, MSubs brings extensive technical expertise to the project. The SDA assessed that the company is best positioned to lead the trials while ensuring submarine safety.

Initial work will repeat the S201 trial series — originally conducted on a smaller extra-large autonomous underwater vehicle under the 'Manta programme' — drawing on established experience to build a foundation for trials on the larger Excalibur hull.

XV Excalibur: Pathfinder for Royal Navy Autonomous Underwater Operations

Built under the CETUS programme, XV Excalibur measures approximately 12 metres (39 ft) in length and 2 metres (6.5 ft) in width, with a displacement of around 19 metric tonnes (21 short tons). It is designed to test the Royal Navy's transition toward autonomous underwater warfare.

In terms of performance, Excalibur has a mission range of 1,600 km (1,000 miles), can dive deeper than any crewed submarine currently in Royal Navy service, sustain operations for up to five days on a single mission, and carry additional payloads and power supply equipment as required.

The Royal Navy positions Excalibur as an experimental platform for shaping future uncrewed underwater systems within a 'hybrid force structure,' and it is not intended for operational use at this stage. The vessel sits within the Royal Navy's Fleet Experimentation Squadron, overseen by the Disruptive Capabilities and Technologies Office, and operates alongside the surface trials vessel XV Patrick Blackett.

MSubs stated on LinkedIn: "The programme about to begin will focus on platform and payload trials, helping to develop an understanding of the role that large uncrewed underwater systems could play in future maritime capability."

CETUS Programme Milestones and AUKUS Transatlantic Remote Control Tests

At a naming ceremony held in May 2025, Commodore Marcus Rose, Deputy Director Underwater Battle Space Capability, said the upcoming trials would lay critical groundwork for the Royal Navy's ability to operate large uncrewed vehicles underwater.

Also in 2025, the Royal Navy successfully tested long-range communications control of Excalibur during exercises conducted under the AUKUS trilateral security partnership between the United States, Australia, and the United Kingdom. During the test, a remote operations centre in Australia controlled Excalibur as it operated in UK waters — a distance of more than 16,000 km (10,000 miles). Excalibur is based at HM Naval Base Devonport (HMNB Devonport) in Plymouth.

The SDA views the current contract with MSubs as only the first phase of a long-term trials programme. As understanding of the vessel's performance deepens, opportunities to extend operational endurance are expected to follow. The SDA also plans to seek diverse payload solutions from multiple suppliers to continuously enhance the programme's overall capability.

Source: UK Defence Journal

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