UK Hands Over Uncrewed Submarine to Royal Navy

XV Excalibur XLUUV | Photo: Submarine Delivery Agency, UK Ministry of Defence

The UK’s development of autonomous undersea capabilities advanced further with the formal handover of XV Excalibur, the Royal Navy’s first Extra-Large Uncrewed Underwater Vehicle (XLUUV). Excalibur, a 12-metre vessel displacing 19 tonnes, is the largest uncrewed submarine yet operated by the Navy and marks the culmination of Project Cetus, delivered by the Submarine Delivery Agency (SDA) in partnership with MSubs Ltd.

Unveiled in May 2025 at His Majesty’s Naval Base Devonport, Excalibur will now undergo two years of extensive sea trials to assess its operational potential and evaluate a range of payloads and missions. The SDA’s Autonomy Unit has led the programme, which aims to build confidence in large autonomous underwater systems and determine how such platforms may be integrated into future naval operations.

Shortly after its naming ceremony, Excalibur demonstrated long-range remote operation during Exercise Talisman Sabre in August. The Royal Navy controlled the XLUUV in UK waters from an operating centre in Australia, more than 10,000 miles away. The demonstration formed part of AUKUS Pillar 2 cooperation and represented the first interoperability trial of XLUUV capabilities between the UK and Australia.

The vessel later completed what the SDA described as a world-first quantum technology trial at sea, carrying the “Tiqker” quantum optical atomic clock developed by Infleqtion. The system aims to improve underwater navigation accuracy by reducing reliance on traditional timing systems that can drift over time. Quantum-based timing offers the potential for submarines to remain submerged and undetected for longer without the need for external signals such as GPS.

The SDA noted that the quantum trial was delivered six months ahead of schedule, following extensive collaboration between the Autonomy Unit, MSubs, Infleqtion and the Royal Navy.

Since its launch in February 2025, Excalibur has completed multiple acceptance trials and exceeded several initial design specifications. With the platform now transferred to the Royal Navy, further testing will continue to determine how autonomous underwater vehicles could operate alongside crewed submarines in future force structures, including under the emerging Atlantic Bastion concept for protecting underwater infrastructure.