A prototype of the Royal Navy's robotic submarine XV-Excalibur patrolling the waters off Devonport Naval Base in Plymouth, England, and being controlled from a command center in Australia 10,000 miles (16,000 kilometers) away, offers a glimpse of what the future fleet will look like.

XV-Excalibur will meet the public in May 2025

The XV-Excalibur, an extremely large unmanned underwater vehicle (XLUUV) built by Plymouth-based MSubs, was unveiled in May as a demonstration platform to explore how large robotic submarines can best be used to augment the Navy's fleet of nuclear attack submarines. During the two-year test program, Excalibur will study how such submarines can be used for anti-submarine warfare, undersea warfare, and intelligence, surveillance and reconnaissance missions.

By conventional submarine standards, Excalibur seems a bit small. In fact, it's about the same size as the X-Craft midget submarine used by the U.S. Navy during World War II, measuring 39 feet (12 meters) long, 7 feet (2 meters) wide and displacing 19 tons - speed, range and propulsion system are still being kept under wraps.


View of the sea from the perspective of EV-Excalibur

Although small in size, it makes up for it with excellent craftsmanship. Since it requires no crew or support personnel, its interior can be stuffed with a variety of equipment, sensors and payload modules to suit specific missions. As it is still in the experimental stage, the only key component it is missing is weaponry, but it is still the most advanced unmanned submarine in Europe.

The trial was conducted in July 2025 under the auspices of the UK/US/Australia Operation Maritime Exercise as part of the biennial Talisman Saber military exercise, involving 19 countries, including Australia, Canada, Fiji, France, Germany, India, Indonesia, Japan, the Netherlands, New Zealand, Norway, Papua New Guinea, the Philippines, South Korea, Singapore, Thailand, Tonga, the United Kingdom and the United States, with Brunei and Malaysia present as observers.

As well as leveraging Australia's ability to demonstrate the ability to issue commands to autonomous submarines from half a world away, Project Cetus is part of the AUKUS Pillar II treaty, which shares submarine technology and other developments between the United States, United Kingdom and Australia, while helping Australia develop the ability to build and operate its own AUKUS-class nuclear attack submarines.

Royal Navy Captain Keith Taylor, senior responsible owner for UK Maritime Operations, said: "This exercise demonstrates how we can take the knowledge gained from experimentation and apply it to the Royal Navy's growing arsenal of unmanned underwater vehicles; putting experimentation into the hands of warfighters."

Source: Royal Navy