UDT 2025: Royal Navy’s CETUS XLAUV set for sea trials

The CETUS extra-large autonomous underwater vehicle (XLAUV) being developed by Plymouth, UK-based MSubs for the UK Royal Navy (RN) is set to begin sea trials.

“We’re into the trials stages,” Callum McCullough, an MSubs naval architect, stated during a 25 March briefing at the 2025 Undersea Defence Technology (UDT) conference, held in Oslo, Norway.

This next step in programme development follows completion of dockside acceptance tests in March, with CETUS having been launched in late February. Prior to that, factory acceptance testing was completed, involving proof testing of all vessel technologies and concepts, said McCullough. Initial concept development work was completed in 2022.

The sea trials will be a relatively conventional testing process, similar to that for any sub-surface vessel, McCullough explained. Beyond sea trials, McCullough highlighted two other testing and development areas.

First, the system architecture – adapted originally from that used on board MSubs’ M201 Manta submersible, designed itself as a vehicle to progress subsea autonomy – will continue testing and development to build full functionality with CETUS.

Second, said McCullough, “We are into a multi-year support contract with the RN…. There are certain things the RN will want to know and want to test.

“The navy has a fair few specified payloads that we’re going to be trying over the next few months and years. We have a few internally as well that we’d like to experiment with,” he added.

Regarding CETUS’s ‘unique selling point’, “The payload bay is the major thing,” said McCullough. “It’s that capacity to test different ideas within the vehicle.” The payload bay can also be used to test other concepts, such as generating range extension devices, he added.

“[CETUS] is built largely around the payload bay: it’s a ‘pick-up truck of the sea’,” said McCullough.

The payload bay can carry 5 tonnes in mass or 9.3 m³ in volume. It is the central module within the vehicle, which is 12 m long, 2 m wide and weighs 20 tonnes. CETUS can be carried within a 40 ft (12.2 m) ISO container.

The RN’s requirement is for a representative XLAUV that provides an adaptable testbed and capacity to improve and scale up uncrewed vehicle capability. Under a November 2022 GBP15.4 million (EUR 18.41 million) contract, CETUS is being procured by the UK’s Submarine Delivery Agency Autonomy Unit to support technology development for Project CABOT: a programme building persistent, wide-area surveillance mass for anti-submarine warfare (ASW) within the RN’s wider Spearhead programme for enhancing North Atlantic ASW capabilities.