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DARPA project tests a new generation of autonomous vessels, without internal areas for sailors, in a proposal that changes the traditional logic of military naval construction and expands the debate on sea operations.
The USX-1 Defiant, an autonomous military ship developed in the United States to sail without a crew, has entered a prolonged demonstration phase at sea after completing initial tests in the state of Washington.
The vessel is about 55 meters long, weighs 240 metric tons, and was designed to operate without receiving people on board, which eliminates common structures in traditional ships, such as command bridge, accommodations, and internal areas intended for the crew.
Developed by DARPA, the advanced research agency of the US Department of Defense, the ship is part of the No Manning Required Ship program, known by the acronym NOMARS.
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The proposal is to test a naval architecture where the absence of crew members is not a later adaptation, but a premise of the project from the construction of the hull to the control and maintenance systems.
Autonomous ship was designed without space for crew
The Defiant was christened on August 11, 2025, at the Everett Ship Repair shipyard in Everett, Washington.
The ceremony followed the naval tradition of breaking a bottle on the hull and presented a vessel that, according to DARPA, was conceived from the start to never accommodate a human on board.
In the configuration released by the agency, there is no cabin for the commander, rooms, living areas, or internal passages intended for the circulation of sailors.
Since the project does not foresee a crew, navigation, propulsion, control, and monitoring systems need to function without an onboard team to make routine adjustments or intervene directly during the mission.
This feature differentiates the Defiant from ships called “optionally manned,” which can operate with or without people.
In the case of the USX-1, the absence of humans is permanent, according to DARPA, and affects the hull design, internal distribution, weight, and systems necessary to maintain navigation for long periods at sea.
Absence of crew changes hull design
In a traditional ship, a significant part of the project needs to meet human permanence requirements.
This includes command bridge, kitchen, bathrooms, accommodations, ventilation, access routes, stairs, corridors, safety systems, and workspaces for the crew.
In the USX-1 Defiant, these structures are not part of the design informed by DARPA.
By removing elements associated with human presence, the program seeks to evaluate engineering gains in areas such as size, cost, reliability, hydrodynamic efficiency, open sea resistance, and protection against interference actions.
These objectives are presented by the agency as part of the goals of NOMARS.
The change also influences the manufacturing process.
According to DARPA, the Defiant has a streamlined hull to facilitate production and maintenance in common port facilities and level III shipyards, typically used for yachts, tugboats, and service vessels.
With this, the project tests a construction route less dependent on large military shipyards.
First Open Sea Crossing
After the christening, the Defiant underwent final tests before heading out to sea.
On September 4, 2025, DARPA reported that the vessel began an extended demonstration of endurance and reliability after performing pre-departure checks near Port Angeles, also in Washington state.
On September 8, the ship arrived at Port Hueneme, California, after completing its first open sea crossing.
According to the agency, the journey covered more than 1,100 nautical miles and was completed in five days, from Port Angeles.
The arrival at the Californian base allowed for new tests in an area used by the US Navy in activities with unmanned systems.
Military personnel from USVRON One squadron accompanied the evaluation to observe the autonomous ship’s performance in maneuvers and procedures related to naval operations.
Refueling at Sea Without People Onboard
During the stage at Port Hueneme, the NOMARS team demonstrated a refueling procedure at sea without crew on the Defiant.
For the test, water was used instead of fuel, but DARPA reported that the demonstration aimed to replicate the operational concept of refueling as closely as possible.
The operation included line passing, connecting the refueling probe, and pumping, without any person onboard the USX-1.
The agency also reported that the ship performed high-speed maneuvers, approached 20 knots in a straight line, and completed entries, exits, dockings, and undockings using its autonomy system.
This type of trial is necessary to evaluate long-duration missions, as an unmanned vessel cannot rely on sailors to receive hoses, adjust cables, or perform common physical tasks in naval operations.
In this context, autonomy needs to encompass not only route navigation but also port procedures, fault response, and interaction with other means at sea.
Resistance to operate in the open ocean
During the christening ceremony, Greg Avicola, NOMARS program manager, stated that the Defiant challenges the idea that it would not be possible to build a ship capable of operating in open sea without people.
According to him, the vessel was designed for prolonged journeys, can operate in sea state 5 without loss of performance, and survive more severe conditions, resuming operations after storms pass.
Avicola also said that the ship is not “wider than it needs to be” to accommodate its equipment and that there are no “human passages” that designers need to worry about.
The statement summarizes the technical logic presented by DARPA: remove from the design everything that exists only to allow the presence of crew members.
The absence of people on board, however, transfers some of the challenges to the reliability of the systems.
Without sailors to replace parts, fix mechanical problems, or perform emergency repairs, the ship needs to keep equipment running for long periods in a maritime environment, where corrosion, vibration, waves, and weather affect the operation of vessels.
U.S. Navy technology demonstrator
The USX-1 Defiant is classified by DARPA as a technology demonstrator.
Its main function is to gather data on engineering, autonomy, endurance, and maintenance in a vessel designed without human spaces, and not to immediately replace manned ships in operation in the U.S. fleet.
After the demonstration at sea, the agency’s announced plan is to transfer the vessel to the U.S. Navy’s Unmanned Maritime Systems office, known as PMS 406.
DARPA states it is working with the Navy to define ways to transition the technologies tested in NOMARS for future uses.
The budget also indicates official interest in medium-sized autonomous vessels.
According to DARPA, the U.S. Congress allocated $2.1 billion for the development, acquisition, and integration of medium-sized unmanned surface ships built specifically for this purpose.
When transferred to PMS 406, the Defiant is expected to become, according to the agency, the first medium-sized unmanned surface ship of the Navy designed to operate exclusively autonomously, rather than a hybrid model with manned and unmanned operation.
USX-1 Defiant and the advancement of autonomous ships
The USX-1 Defiant allows observation of how the design of a vessel changes when human presence is no longer considered a design requirement.
Instead of adapting a conventional ship to operate with automation, NOMARS starts from a configuration where autonomous systems, simplified hull, and absence of internal spaces for crew are treated as central elements.
For now, there is no public confirmation that the Defiant will be mass-produced or give rise to a large-scale operational class.
The available information indicates that the ship remains a demonstrator, with data being collected by DARPA and the US Navy during sea trials.
Even at this stage, the project broadens the scope of testing with autonomous maritime systems.
The Defiant does not fall under small aquatic drones but is a vessel of hundreds of tons, capable of ocean crossing, port maneuvers, and refueling simulations without crew on board.
Based on the results collected from the tests, the US Navy will be able to assess which NOMARS technologies can be integrated into future naval platforms.
Until then, the Defiant remains a case study on military vessels without a bridge, without accommodation, and without internal areas intended for sailors.
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