ANNAPOLIS, Md. — The U.S. Navy on Tuesday welcomed its third Overlord unmanned surface vessel into the fleet, as the service prepares to ramp up its USV experimentation at sea and ashore.

Mariner, built by Gulf Craft in Louisiana and managed by prime contractor Leidos, was delivered in March and christened Aug. 23 at the U.S. Naval Academy. It is already outfitted with a government-furnished command-and-control system, a virtualized Aegis Combat System, an autonomous navigation system and more. After a few more upgrades and testing, it will head out to California and begin operations in fiscal 2023, the Navy’s program executive officer for unmanned and small combatants, Rear Adm. Casey Moton, told reporters during a tour here.

Mariner’s sister ships, Nomad and Ranger, recently participated in the Rim of the Pacific naval exercise in Hawaii. The addition of Mariner to the USV fleet will add both volume and new capabilities as the Navy tries to learn more about operating unmanned craft and decide what the future hybrid manned-unmanned fleet ought to look like, Moton said.

The Navy’s test plan includes both land-based and at-sea testing, he said. During land-based testing, the Navy can more easily install new items, can run tests for longer durations and in more controlled conditions, and can update systems more easily as test results highlight needed fixes.

At sea, though, he said “you’re in the dynamic marine environment, with the ship moving around, and in a corrosion environment, and watch standers having to move around ... dynamic loads and all kinds of things. There is absolutely a place for both.”

The Navy will ultimately have seven USVs to experiment with at sea: Nomad, Ranger, Mariner and fellow Overlord USV Vanguard, which is under construction at Austal USA with prime contractor L3Harris; as well as Medium USV prototypes Sea Hunter and Sea Hawk, which also participated in RIMPAC, and a third medium-size ship on contract with L3Harris.

Moton argued it’s important to have so many at-sea test platforms because of the scale of testing the Navy is trying to do, working through different vendors’ systems for perception, autonomy, machinery control and more, as well as testing out a number of potential payloads.

A new feature built into Mariner will also allow for some unique concept of operations testing at sea: the virtualized Aegis Combat System will actually allow Mariner to control another USV, Moton said.

“Now we can take two of our USVs and go out and do multi-vessel ops and control and not necessarily have to take a [destroyer] off of actual fleet operations to go do that. It gives us that ability to just get there that much more quickly,” he said.

A program official added during the tour that the USV Division 1 staff in California, who could in the future operate USVs from an ashore unmanned operations center or from aboard a Navy ship such as a destroyer, could actually use Mariner as a training vessel, embarking it as they would a destroyer and controlling another USV manually from Mariner’s combat system. USV Division 1 officials were able to collaborate with destroyers during RIMPAC, though access to such warships for experimentation is far from the norm because of busy training and deployment schedules. That’s why officials hope Mariner could serve as something of a training ship for the division staff as they learn how to employ a USV from a ship at sea.

As for the land-based testing, Moton said the Navy is moving ahead with industry-led testing of engines for unmanned vessels even as its official USV land-based engineering site is under construction at Naval Surface Warfare Center Philadelphia. L3Harris has an MUSV plant in Camden, N.J., that would be transitioned to the Navy facility just across the river if the service decides to move ahead with those types of USVs. The Navy is currently committed to a large robotic-ship program (LUSV) and is still weighing the value of medium-size ships against the capabilities that small drones in large numbers could bring.

On LUSV, a variety of potential engines are being tested ashore by their various vendors — which Moton said is a good thing for technology development and for keeping the program competitive — and that work will also be moved to Philly when the new test center is ready.

Despite all the testing taking place, Navy officials during the tour said commercial industry has done quite a bit of work already to mature autonomy systems on ships. In the case of Mariner’s parent design, autonomy features were optimized for the fast supply vessel to bring people and materials to oil rigs with a crew of just six on the 194-foot boat.

Because of the pre-existing emphasis on autonomy and redundancy to support a small crew, the ship was already designed with five water jets, each with their own engine and drive train and an ability to switch between them if one experienced a problem. The Cummins engines were built with an option that avoids the need for periodic oil changes — something that would otherwise prevent USVs from operating months at a time without a crew — using a system that automatically burns off the old lube oil and adds in new lube oil.

The Navy went further and added in a whole web of cables that connect sensors to ship systems and enable the machinery control system to autonomously monitor hull, mechanical and electrical systems and shift between redundant systems when needed.

Brian Fitzpatrick, the principal assistant program manager for USVs at the unmanned maritime systems program office within PEO USC, said the Navy had collected 400 terabytes of data from Nomad, Ranger, Sea Hunter and Sea Hawk at RIMPAC and that his office would spend the coming months parsing through that data to understand both system performance at sea and to refine what data they wanted to continue collecting in the future.

Fitzpatrick said the Navy was looking forward to the delivery of its final OUSV prototype, Vanguard, which takes Mariner’s parent design and scales it up to a 205-foot design. Because the vessel is larger, it can hold more fuel and therefore gain even greater range, and it can haul even heavier payloads. Fitzpatrick said Vanguard would push the limits of what a vessel of this size class could do for the Navy.

The program-of-record LUSV’s design hasn’t been finalized yet but will certainly be larger than Mariner and even Vanguard. Fitzpatrick and Moton said all the testing at sea and ashore will apply equally to a future LUSV and a potential MUSV from an engineering perspective. From a concept of employment perspective, the Navy knows just what it wants from LUSV — to serve as an adjunct missile-launcher — but testing will help inform whether hauling around sensors and electronic warfare packages on a vessel of this size is worth the price tag.

“I think it’s completely healthy for the top levels of the Navy to be having that question about what a hybrid fleet, manned-unmanned, looks like. And we are essentially providing the data and the feedback on [concepts of operations] that’s supporting that discussion,” Moton said.

Megan Eckstein is the naval warfare reporter at Defense News. She has covered military news since 2009, with a focus on U.S. Navy and Marine Corps operations, acquisition programs and budgets. She has reported from four geographic fleets and is happiest when she’s filing stories from a ship. Megan is a University of Maryland alumna.

More In Naval