US DARPA tests autonomous at-sea refueling for USV Defiant under NOMARS program

January 2, 2025, by Fatima Bahtić

The US Defense Advanced Research Projects Agency (DARPA) has completed the first test of at-sea refueling designed for use with the unmanned surface vessel (USV) Defiant.

As disclosed, the USV Defiant is intended to operate autonomously for long durations at sea and is designed from the ground up with no provision, allowance, or expectation for humans on board. The tests are part of DARPA’s No Manning Required Ship (NOMARS) program.

US Navy PMS-406 (the Unmanned Maritime Systems Program Office) and USV Squadron 1 (USVRON-1) conducted the test in partnership, using two of the PMS-406 experimental USVs, Ranger and Mariner.

According to DARPA, fueling at sea (FAS) for USVs presents a problem that needs to be solved as current FAS solutions use personnel to handle lines and hoses on the platform being refueled.

Requiring personnel on the USV for the operation adds significant constraints on USV design and operations, as the vessel must then be designed with considerations for safety of the humans on board, even if for a short period of time, it was highlighted. It can also be risky and sometimes dangerous to transport personnel to a USV in rough seas or high winds.

The NOMARS FAS approach is designed for operation without any human intervention on the USV, but does have humans on the refueling vessel. T

he FAS approach mirrors a standard refueling concept of operations (CONOPs) as closely as possible to be familiar with Military Sealift Command (MSC) oiler crew and reduce their learning curve.

DARPA has worked closely with MSC’s Taluga Group throughout the NOMARS program to advise on the development of the FAS system and CONOPs.

For the recent test, the USV Ranger carried a receiving station representative of the system that will be on the NOMARS USV Defiant.

Meanwhile, USV Mariner carried a refueling “mini-station,” designed by NOMARS’ contractor Serco. While there were personnel aboard both vessels during the event, no people were involved with operations on the receiving side.

As revealed by DARPA, the team demonstrated all parts of the system CONOPs while underway, including passing the lead line to the refueling side, passing and connecting the refueling probe to the USV side, and pumping water.

This was the first on-water test of the system, and all parts of the operation were successfully demonstrated, according to DARPA.

The next FAS test will take place with NOMARS USV Defiant during its sea trials period. Defiant is a 180’, 240-metric-ton lightship currently nearing completion of construction and is scheduled to depart for its multi-month at-sea demonstration in spring 2025.

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