UK Awards $8.8M Contract for Trials of 21-Ton Submarine Drone XV Excalibur

MSubs has received an $8.8 million contract to initiate testing of the extra-large submarine drone XV Excalibur, also known as CETUS, with the objective of validating its autonomous underwater operations and payload capabilities.

The trials will be conducted at MSubs’ Plymouth facilities and nearby sea areas, continuing through 2028.

This contract was awarded by the UK Submarine Delivery Agency (SDA) under the Procurement Act 2023. MSubs has served as the sole developer of the unmanned vessel within the CETUS program.

The initial phase involves replicating the S201 trials previously performed on a smaller extra-large autonomous underwater vehicle as part of Project Manta. According to the SDA, this prior experience positions MSubs advantageously for the Excalibur trials.

The SDA determined that MSubs is best equipped to conduct these trials while ensuring the safety of the submarine drone.

XV Excalibur submarine drone

Constructed under Project CETUS, the XV Excalibur measures 39 feet (12 meters) in length and 6.5 feet (2 meters) in width, with a displacement of approximately 21 tons (19 tonnes).

The vessel is capable of missions extending up to 1,000 miles and can dive deeper than any manned submarine in the Royal Navy. It can operate continuously for up to five days and supports additional payload and power supply configurations depending on mission requirements.

The Royal Navy plans to utilize Excalibur to inform the development of future unmanned undersea systems within a mixed force framework. The vessel is not designed for combat roles.

Excalibur is assigned to the Royal Navy’s Fleet Experimentation Squadron under the Disruptive Capabilities and Technologies Office, alongside the surface experimentation vessel XV Patrick Blackett.

In a LinkedIn statement, MSubs noted, “The forthcoming program will focus on platform and payload trials, helping to further understand the role large uncrewed underwater systems can play in future maritime capability.”

Previous wins for Project CETUS

At the May 2025 naming ceremony, Commodore Marcus Rose, Deputy Director of the Underwater Battlespace Capability, stated that the upcoming trials would enhance the Royal Navy’s understanding of managing large uncrewed underwater vessels.

In 2025, the Royal Navy successfully conducted a long-distance communication test with the new XLUUV during an exercise involving the US, Australia, and the UK under the AUKUS security partnership.

During this test, Excalibur was submerged in UK waters at HMNB Devonport in Plymouth and remotely controlled from an operating center in Australia over a distance exceeding 10,000 miles.

The SDA views the contract with MSubs as the initial phase of extended trials. With shared insights among stakeholders, there is potential to increase operational durations and explore various payloads from different suppliers to advance the project’s capabilities, as reported by the UK Defence Journal.