U.S. Navy demonstrates at-sea refueling for unmanned surface vessel

The U.S. Navy demonstrated a system last month that can refuel an unmanned surface vessel at sea without any crew on board, a step toward keeping robotic boats on station indefinitely instead of returning to port when they run low on fuel.

The Naval Air Warfare Center Weapons Division ran the demonstration off the coast of Virginia using a towed connector that repeatedly captured, refueled and released a Navy-owned USV called the T38. A Navy-industry team went from concept to on-water testing in seven months, according to the warfare center.

The T38, also known as the Devil Ray, is built by Maritime Tactical Systems Inc. and measures 38 feet (11.1 meters) long, with a payload capacity of up to 4,000 pounds (1,814 kilograms) and burst speeds exceeding 70 knots depending on its engine configuration. The Navy operates this particular T38 through its Blue Water Instrumentation program, based at the Naval Air Warfare Center Weapons Division’s Point Mugu Sea Range in California. In May, the same vessel completed a record 192-hour autonomous mission 400 nautical miles (740 kilometers) off the California coast without any chase boats or escorts.

“At Naval Air Warfare Center Weapons Division, our immediate focus is supporting hypersonic and precision long-range fires testing, where flight profiles can extend thousands of miles beyond fixed-range boundaries and require data-collection assets to be distributed across a vast area,” said Spencer Holloway, director of the Blue Water Instrumentation program’s future capabilities office. “But the underlying challenge applies more broadly. Every time an unmanned vessel must return to port for fuel, we lose persistence, reduce coverage and redundancy, and interrupt the mission.”

During the Virginia demonstration, the training support vessel USNS Vindicator towed the refueling system and transferred a total of 400 gallons (1,514 liters) of fuel to the T38 across dozens of full-cycle exercises at sea, in addition to pier-side testing. The refueling system completed roughly 100 connection cycles over the course of a few days leading up to and including the event, which took place in the waters off Joint Expeditionary Base Little Creek-Fort Story, Virginia.

A refueling probe, left, on the T38 unmanned surface vessel prepares to mate with a towable capture and connection device during a refueling demonstration in the water off Joint Expeditionary Base Little Creek-Fort Story, Va., Aug. 11, 2026.

Ronald Raymer, branch head for capability, innovation, science and technology integration at U.S. Fleet Forces Command, said the capability could change how the Navy uses unmanned vessels operationally, not just for testing.

“This will allow us to have greater reliance on unmanned vessels … and we can push the USV into higher threat areas without risking manned vessels and personnel,” Raymer said. “It will also allow us to distribute greater capability into an area without having to invest in large, expensive manned vessels, and the refueling supports that.”

U.S. Fleet Forces Command, Naval Surface Warfare Center Dahlgren Division and Naval Surface Warfare Center Carderock Division sponsored the demonstration. The Littoral Combat Ship Mission Modules Program Office and the Navy’s Portfolio Acquisition Executive for Robotics and Autonomous Systems provided contracting support that allowed the Blue Water Instrumentation team to work directly with industry partners on the project.

“Working directly with our industry partners allowed us to bring the platform, control systems, operators and engineers together as one integrated team,” Holloway said. “We could make changes, test them on the water and iterate quickly based on what we observed.”

The program’s next milestone is a fully autonomous, end-to-end refueling demonstration that will combine vessel rendezvous, approach, capture, fuel transfer, disconnection and return to mission into a single automated sequence, according to the warfare center.