It’s been a busy year for the SDA’s Autonomy Unit who have achieved several milestones with XV Excalibur, the UK’s first uncrewed submarine.

Officially classified as an Extra-Large Uncrewed Underwater Vehicle (XLUUV), Excalibur is a 12-metre experimental vessel. At a displacement of 19 tonnes, it’s the largest uncrewed underwater vessel ever trialled by the Royal Navy.

The culmination of Project Cetus, it’s been developed in under three years by the SDA in partnership with MSubs Ltd. Sponsored by the Royal Navy, Project Cetus aims to build trust in Autonomy and be a testbed to assess military payloads and missions.

Official naming ceremony

In May 2025, Excalibur was named and unveiled at a ceremony in His Majesty’s Naval Base (HMNB) Devonport. It’ll now spend the next two years carryin

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