The 180-foot-long, 240-metric-ton demonstrator features a simplified hull to enable rapid production and maintenance in port facilities or Tier III shipyards that traditionally service yachts, tugs, and workboats. Built with no provision for human crew, Defiant is intended to deliver advantages in size, cost, at-sea reliability, hydrodynamic efficiency, and survivability, with the ability to operate in sea state 5 without performance loss and withstand harsher conditions.
“Defiant is a tough little ship and defies the idea that we cannot make a ship that can operate in the challenging environment of the open ocean without people to operate her,” said NOMARS Programme Manager Greg Avicola. “While relatively small, Defiant is designed for extended voyages in the open ocean, can handle operations in sea state 5 with no degradation and survive much higher seas, continuing operations once the storm passes. She’s no wider than she must be to fit the largest piece of hardware and we have no human passageways to worry about.”
Following final systems testing, the vessel will begin an extended at-sea demonstration of its reliability and endurance. “Defiant class vessels provide cost-effective, survivable, manufacturable, maintainable, long-range, autonomous, and distributed platforms, which will create future naval lethality, sensing, and logistics,” said DARPA Director Stephen Winchell. “Defiant will protect and expand the capabilities of manned ships, multiply combat power at low cost, and unlock new American maritime industrial capacity.”
Anthony Kirby, Serco Group Chief Executive, said: “Defiant marks a first in naval ship design and ushers in an exciting new stage for the NOMARS programme and the US Navy. We are incredibly proud to have played our part in developing genuinely groundbreaking new capabilities for the Navy in vessel autonomy and at-sea refuelling. This watershed is the first time a ship has been designed entirely without human crew members in mind, a significant step towards the US Navy’s ambition of a fleet of USVs capable of operating in contested waters and other dangerous environments without putting the lives of human sailors at risk.”
Upon completing the demonstration, Defiant will be transferred to the U.S. Navy’s Unmanned Maritime Systems Program Office (PMS 406) as its first solely autonomous medium unmanned surface vessel. DARPA is working with the Navy to ensure the technologies are scalable, rapidly transferable, and compatible with international defence partnerships. In July, Congress appropriated $2.1 billion for the development, procurement, and integration of purpose-built medium unmanned surface vessels.
Defence remains a major part of Serco’s portfolio, accounting for over 80% of order intake in the first half of 2025. This includes recent contract awards such as more than £1 billion in Maritime Services for the Royal Navy, a ten-year Armed Forces Recruitment Service contract worth up to £1.5 billion, a $96 million technical services agreement to modernise the US Navy’s guided missile frigates, and a $247 million contract to support the US Army’s Holistic Health and Fitness System.
