Stirling Castle-class

HMS Stirling Castle (M01) is a mine countermeasures autonomous systems platform operated by the Royal Navy. Designed by Rolls-Royce as a VARD UT 776 CD offshore support vessel, the ship was built by Vard Brăila in Romania, laid down in October 2011, and launched in March 2013. It originally operated under the name Island Crown for Island Offshore, supporting oil, gas, and offshore renewable energy operations, including the construction of the East Anglia Array wind farm. In February 2023, the United Kingdom Ministry of Defence purchased the vessel for £40 million to convert it into a naval trials platform following increased concerns over subsea infrastructure protection.

The vessel is designed to serve as an offshore forward operating base, mothership, and training platform for Mine Countermeasures Maritime Autonomous Systems (MCM MAS) and uncrewed aerial vehicles. Propulsion is provided by four Bergen Engines C25:33L-6 diesel engines driving two Kongsberg azimuth thrusters and three Kongsberg bow thrusters. The ship is equipped with a flight deck helipad and a main crane featuring a safe working load of 10 tonnes at a 34-metre radius and 5 tonnes at a 40-metre radius, tailored for launching and recovering uncrewed craft.

Conversion for naval service took place at HMNB Devonport. In July 2023, the vessel conducted its initial trials deploying Royal Navy autonomous motor boats Apollo, Hydra, and Hazard. Between January and March 2024, the ship completed operational sea training prior to joining the Mine and Threat Exploitation Group at HMNB Clyde.

The vessel formally entered service with the Royal Fleet Auxiliary (RFA) as RFA Stirling Castle in April 2024. In August 2024, damage to the main crane rendered the ship temporarily incapable of boat operations. Although the crane was repaired by October 2024, RFA workforce shortages kept the ship inactive, requiring the Marine Services vessel SD Northern River to temporarily fill the command and support role.

To address RFA staffing shortages, the vessel was transferred to the Royal Navy and commissioned as HMS Stirling Castle on 21 July 2025, homeported at HMNB Portsmouth. In May 2026, HMS Stirling Castle transited to Gibraltar to deliver the autonomous motor boats RNMB Ariadne and RNMB Halcyon to RFA Lyme Bay.