U.S. Navy Tests Robotic At-Sea Refueling to Extend T38 Unmanned Surface Vessel Endurance.

The U.S. Navy has repeatedly refueled a T38 unmanned surface vessel at sea using Sealartec’s robotic capture and connection system, according to an August 11, 2026 demonstration off Virginia. The capability could keep unmanned vessels on station longer without returning to port, extending their reach and persistence during distributed maritime operations.

The Navy-industry team transferred 400 gallons of fuel and completed about 100 connection cycles under operational sea conditions, demonstrating repeatable capture, refueling, and release of the T38. Reliable robotic replenishment could reduce a major endurance constraint on unmanned surface vessels and support sustained sensor coverage and mission presence far from established logistics infrastructure.

Related Topic: U.S. Navy To Field More Than 30 Medium Unmanned Surface Vessels In Indo-Pacific By 2030 To Counter China

The U.S. Navy has successfully demonstrated repeated robotic at-sea refueling of its T38 unmanned surface vessel marking a major step toward longer-duration autonomous maritime operations with reduced dependence on port infrastructure and crewed logistics support (Picture Source: Naval Air Warfare Center Weapons Division)

The U.S. Navy has demonstrated repeated robotic at-sea refueling of its T38 unmanned surface vessel using Sealartec’s towable capture and connection device, marking a significant step toward sustained unmanned maritime operations without routine returns to port. Led by Naval Air Warfare Center Weapons Division’s Blue Water Instrumentation program off Virginia, the test directly addresses one of the main endurance limits affecting unmanned vessels: maintaining fuel, sensor coverage, and mission presence over extended distances without increasing reliance on crewed logistics ships. The capability is particularly important for future distributed naval operations, where unmanned vessels may be required to remain on station for long periods while operating far from established support infrastructure.

During the August 11, 2026 demonstration off Joint Expeditionary Base Little Creek-Fort Story, the training support vessel USNS Vindicator (TSV 5) towed the robotic refueling device while the Navy-industry team repeatedly captured, refueled, and released the T38 under operational sea conditions. The system transferred a total of 400 gallons of fuel during the event and completed about 100 connection cycles over several days, giving engineers a substantial data set on repeatability, reliability, and maneuvering performance. Repeated successful connections are particularly significant because they demonstrate that the concept can be evaluated as a sustained operational process rather than as a one-time technical achievement.

The T38 is a Navy-owned, remotely controlled unmanned surface vessel built by Maritime Tactical Systems Inc. (MARTAC), while Sealartec developed the towable capture and connection device, or TCCD, used to establish the refueling interface. The Navy and its industry partners moved from concept development to on-water testing in only seven months, combining the vessel, robotic connector, control systems, engineers, and operators into a single development effort that could be modified and retested rapidly as technical issues emerged. This accelerated development cycle reflects a broader Navy effort to shorten the transition from experimental technology to operationally relevant capability, particularly in areas where unmanned systems could reduce personnel exposure and expand maritime reach.

The operational significance of the demonstration extends well beyond increasing the endurance of a single T38. NAWCWD’s Blue Water Instrumentation organization is examining unmanned vessels as distributed instrumentation assets for hypersonic weapons and precision long-range fires testing, where weapon trajectories can extend thousands of miles beyond fixed-range boundaries and require sensors to be dispersed across vast maritime areas. Robotic refueling could keep these data-collection vessels positioned along extended test corridors for longer periods while reducing the need to rotate them back to port or dedicate additional crewed support ships to sustain their presence. That persistence is critical for maintaining continuous telemetry, tracking, and test coverage across increasingly long weapon flight profiles.

For the wider U.S. Navy, this endurance challenge is central to whether unmanned surface vessels can become persistent operational assets rather than periodically deployed experimental systems. Every return to port for fuel removes a vessel and its sensors from the assigned area, reduces redundancy, creates gaps in surveillance or test coverage, and imposes additional transit and logistics requirements. Underway robotic refueling could increase the practical value of unmanned fleets by allowing more vessels to remain dispersed across large operating areas for longer periods. It could also reduce the number of crewed support ships required to sustain those operations, freeing high-value vessels for other missions while lowering the manpower burden associated with distributed maritime presence.

The concept also has direct relevance to contested maritime operations. U.S. Fleet Forces Command officials involved in the demonstration highlighted the potential to send unmanned vessels into higher-threat areas without exposing sailors and expensive crewed warships to the same level of danger. If unmanned surface vessels can be sustained at sea through robotic replenishment, commanders could maintain sensors, communications relays, electronic warfare equipment, or other mission payloads closer to adversary threat zones while keeping major crewed combatants at greater stand-off distances. In practical terms, greater unmanned endurance could expand the Navy’s ability to maintain persistent surveillance, build a more resilient maritime sensor network, and distribute mission capability across multiple lower-risk assets.

Repeated capture and connection are especially important because robotic refueling at sea requires far more than transferring fuel between two vessels. The T38 must approach a moving connector under tow, compensate for vessel motion and sea conditions, enter the required capture geometry, establish a secure connection, remain stable during transfer, and disengage safely before returning to its mission. Completing about 100 connection cycles allows engineers to identify limits in control precision, mechanical reliability, capture tolerances, operator workload, and overall procedure under realistic maritime conditions. The test series provides the Navy with valuable information on how the refueling system behaves across repeated evolutions, which is essential before the technology can support routine fleet operations.

The current sequence still includes human control, but the Navy’s next milestone is an end-to-end autonomous refueling evolution covering rendezvous, approach, capture, fuel transfer, disconnection, and return to mission as one continuous process. Blue Water Instrumentation is now working to reduce command-and-control latency during operator-assisted maneuvering and integrate next-generation local positioning systems capable of providing the precision required for autonomous terminal approach. Reliable automation at this stage will be critical if the Navy intends to scale unmanned refueling beyond isolated demonstrations and support larger numbers of vessels operating over extended distances. Removing the need for constant operator input would also reduce communications dependence and make sustained unmanned operations more resilient in environments where links may be degraded, jammed, or intermittent.

If the U.S. Navy can move from repeated operator-assisted connections to a reliable autonomous rendezvous-to-return-to-mission sequence, robotic refueling could remove one of the most persistent logistical constraints limiting unmanned surface vessel operations. For hypersonic and precision long-range weapons testing, the capability could keep instrumentation vessels distributed across enormous ocean test corridors for longer periods; in future combat operations, the same technology could allow unmanned sensors and mission systems to remain inside contested regions with fewer interruptions, lower personnel exposure, and reduced dependence on large crewed support ships. The August demonstration represents more than a successful fuel-transfer event: it is an important step toward the autonomous sustainment architecture required for a persistent, distributed, and operationally scalable unmanned fleet.

Explore More Defense News

• Land Defense News
• Naval Defense News
• Defense Aerospace News

Written by Teoman S. Nicanci – Defense Analyst, Army Recognition Group

Teoman S. Nicanci holds degrees in Political Science, Comparative and International Politics, and International Relations and Diplomacy from leading Belgian universities, with research focused on Russian strategic behavior, defense technology, and modern warfare. He is a defense analyst at Army Recognition, specializing in the global defense industry, military armament, and emerging defense technologies.