Unmanned systems at sea offer advantages and face challenges that are often different from those associated with airborne and ground-based systems. For example, in a patrol mission that calls for long endurance at low speed, the size of a manned ship is largely driven by the need to provide tolerable accommodation and stability for the crew—a limit that does not apply to an unmanned surface vessel (USV).

On the other hand, manned craft have long range and payload because of their size, and nobody is interested in a USV weighing several hundred tons. That means that USVs either need a mothership (launch and recovery techniques are still in the works) or may be confined to coastal roles. Also, sensor and communications line-of-sight distances are subject to the unbreakable laws of mast height and horizon distances.

Consequently, fielding USVs and autonomous underwater vehicles (AUVs) may be more a question of matching basic technology to the concept of operations (conops), while applying new technology selectively.

A major French effort, to be unveiled at the Euronaval show in Paris later this month, pulls together USV and AUV technology to create a unique minehunting system including three world-first technologies. The Espadon (Swordfish) project, launched by the DGA French procurement agency in July 2009, is being run by a team comprising naval systems group DCNS, robotics company ECA and Thales.

The centerpiece of Espadon is a 17-meter (58-ft.)-long, 25-ton, boxy-looking catamaran USV named Sterenn Du (“black star” in Breton). Because current French legislation forbids surface vessels from navigating without human beings aboard, Sterenn Du has a small pilot's cabin, set to one side much like an aircraft carrier's island. But the Sterenn Du can also be teleoperated or be completely autonomous.

Sterenn Du's role is to deploy AUVs. It would be brought close to the mission zone by a dedicated mothership of 2,500—3,000 tons, which would remain a safe distance from the minefield. Aboard the Sterenn Du are three AUVs developed by ECA, which constitute its actual mine-hunting and destroying tools.

The biggest technological difficulty was the design of the launch and recovery system, Stephane Meltzheim, head of the Espadon project at ECA, told Aviation Week. It is harder to get two autonomous machines to connect in high seas than in outer space. There are currents, winds and waves to contend with and the DGA specified that the vessels must be operational in Sea State 5. A traditional minehunter cannot operate beyond Sea State 3.

The solution resembles the drogue and hose used in inflight refueling: using one of its world-first features, the Sterenn Du unwinds a cable that the AUV clamps onto and the cable then draws the AUV inside a cage between the two hulls of the catamaran, another first. Meltzheim adds with some pride that there has been close to a 100% success rate in tests with the system, which ECA has patented.

The third innovation is active and passive shock-absorbing systems in the cage, which means the AUV stays as stable as possible despite any movements of the ship. Once the AUV is in its cage, it is brought up inside the Sterenn Du.

Each of the three AUVs has a specific role. The first to be launched would be the DCL (detection, classification and localization) AUV. It is 5 meters long, weighs between 800-1,000 kg (1,764-2,200 lb.), has a range of 40 km (25 mi.) and an endurance of between 10 to 20 hr., depending on the type of battery installed. The DCL vehicle carries a sonar to detect and classify underwater objects. “This vessel has the intelligence to work by itself and overcome any unexpected problems it may come across,” says Meltzheim. The vessel was developed in 2006-09 but the automatic recovery system was added for the Espadon program.

Data collected by the DCL AUV is transmitted back to the mothership, where operators decide what objects need to be observed more closely, then program the second AUV and send it out. “This catamaran AUV, specifically developed for this project, is extremely maneuverable, with two propellers at the front and two at the rear, four cameras, lighting and a small sonar,” Meltzheim explains. “It is programmed with all the [mine-like contacts], which were identified by the DCL, and it observes them one by one,” acquiring still and moving imagery. It goes over each contact at least once and when it has completed its mission, it returns to the Sterenn Du.

At this point, the third AUV comes into play. Until now, the project has used a reusable vehicle which is wire-guided to the mine, drops an explosive charge next to it and retreats before detonating the charge to destroy the mine. “However, the tendency today is toward using expendable and much cheaper kamikaze-style robots, guided to the mine by an operator,” says Meltzheim.

Once sea trials are completed in the next few months, the next step will be to launch a second prototype, which will be co-financed by France and the U.K. in the framework of the November 2010 Lancaster House treaties.

Another major USV development appearing at Euronaval also reflects the use of new and mature technology to match a developing conops: a new and larger version of the Protector USV from Israel's Rafael. Work on the 11- meter craft started about three years ago. After evaluating smaller craft, the developers saw a need for a vessel that could operate in higher sea states, as well as provide better speed and endurance—up to 48 hr. in some conditions—and a bigger payload.

With a larger and more costly USV performing longer and more distant missions, a dual, fully redundant diesel-and-waterjet drive system became a priority to ensure that no single failure would prevent the operator from returning the vessel to base. Redundancy extends to the electrical and control systems, and new features have been added to enhance damage control capabilities and system health monitoring.

The new boat is based on a patented design, optimized for unmanned operation with increased buoyancy and survivability. The aluminum hull is a heavy-duty, rigid, deep-V planning design with sealed bulkheads and a foamed D-collar, designed for performance and high survivability in high seas. The Protector has a crew of two to manage sensors and control the boat, and carries radar and electro-optical sensors and a communications/data link suite that can interface with wide-area systems like those used for maritime surveillance and border patrol.

With its immediate range of vision limited by mast height, the Protector is an interceptor. Once a potential threat is detected, the Protector is sent to intercept the target and identify it using the Toplite stabilized electro-optical turret. The onboard loudhailer system is used to approach the target and determine its intentions. A water cannon can be used for non-lethal engagement, but the Protector also carries the Mini-Typhoon stabilized gun system, and can be fitted with a strike module that includes Spike missiles for long-range precision engagement. The Protector can also be used as an electronic warfare platform to a degree.

The U.S. Navy is looking for a USV in the same size class as the new Protector, as a way of bolstering its mine warfare capability. The service has been criticized for downplaying the importance of mine warfare and is now playing catch-up. But the Navy wants a vessel that can quickly survey a large area to hunt and counter mines at all times, notes Stanley DeGues, senior business development director for Textron subsidiary AAI Advanced Systems, which is developing a common, unmanned surface vessel (Cus-V).

“Only mine ships can do it at night,” DeGues says. “Helicopters can't do that.”

AAI is offering the Cus-V for the Navy's proposed unmanned influence sweep system (UISS), meant to provide Littoral Combat Ships (LCS) with a stand-off, long-endurance, semi-autonomous minesweeping capability to counter acoustic or magnetic influence mine threats in the littorals. The Navy plans to test UISS platforms starting in fiscal 2014 and hopes to have them ready for initial operational capability in fiscal 2016.

For the cost of a single minehunting helicopter, DeGues says, the Navy could buy 8-12 Cus-Vs. A Cus-V is 39 ft. long, has a draft of slightly more than 2 ft. and reaches a top speed of 28 kt. It has a cruising range of about 1,200 nm, can tow up to 5,000 lb. while traveling at about 10 kt., and features a 14-ft. payload bay, as well as an autonomous launch, tow and recovery system to deploy a sweeper.

While being developed with the LCS fleet in mind, the Cus-V is land-transportable, air-transportable in a C-17 and C-5, and can be ferried by ship—even commercial vessels, DeGues says. The Cus-V also could be launched out of the well decks of large-deck Navy amphibian assault ships, he notes. There also are some global queries about the ship, too, for missions like harbor security, he adds. “Internationally, folks are very interested.”

In the AUV world, the Office of Naval Research (ONR) is pressing forward with work on the Large Displacement Unmanned Undersea Vehicle (LDUUV).

A variety of AUVs of various shapes and sizes are in service and in development around the Navy, ranging from the Naval Oceanographic Office's Littoral Battlespace Sensing gliders to the Knifefish mine countermeasures AUV planned for use on the LCS, but these are basically single-mission vehicles. LDUUV is planned to have long endurance and operationally useful speed, autonomy and payload capacity, enabling independent, clandestine operations in forward areas.

Though the Navy has not yet specified which missions the vehicle will perform—an analysis of alternatives (AoA) now being conducted by Naval Sea Systems Command is slated for completion next March—a few possibilities present themselves. The stealth and persistence of a long-endurance AUV will be especially useful for intelligence, surveillance and reconnaissance (ISR) or preparation of operational environment (IPOE) missions, such as bottom mapping. But it is not hard to envision the LDUUV carrying mines, bomblets or miniature torpedoes, and performing missions previously in the domain of manned submarines like the tracking of enemy submarines.

LDUUV could also be uniquely suited to address emerging missions like defense of the pipelines and telecommunications cables that are increasingly vital to the global economy, or attack on an adversary's undersea sensor networks. Simply put, LDUUV will fulfill a persistent ISR and battlespace preparation role, but will also expand the reach of the U.S. submarine force and perform missions that are impossible for anything in the current arsenal. Moreover, it will enter just in time to mitigate the slump in force structure that will hit in the 2020s, as the large Cold War fleet of Los Angeles- class subs retires.

The new craft is different in important ways from failed predecessors like the Mission Reconfigurable UUV (MR-UUV). Released from “the tyranny of the 21-inch tube,” it has more room for energy storage and payloads. It is designed for launch and recovery from a variety of platforms: SSGNs and Virginias via their large-diameter tubes, the Littoral Combat Ship, piers, or contracted merchant ships. Energy technology has advanced since the MR-UUV as well, allowing for greater energy density and longer endurance—though much work remains to be done in this area to produce an operationally useful vehicle. And perhaps most importantly, it has support at the highest levels of the Navy. In February, the chief of naval operations, Adm. Jonathan Greenert, told reporters “I'm very much desirous of that end-state, cross-ocean, as feasible . . . 30-day, 45-day.”

After the LDUUV AoA is completed in 2013, the Navy is likely to issue a formal request for proposals in fiscal 2014, according to a February statement from the LCS program office, its sponsor. In the meantime, ONR plans to produce 10 Innovative Naval Prototype (INP) vehicles, focusing on technologies that will improve energy density, autonomy and reliability. These prototypes will be transitioned from ONR to the fleet after completion of the INP program, and the Navy intends to have a squadron of 10 operational LDUUVs by 2020.

Even more ambitious than LDUUV is a Defense Advanced Research Projects Agency (Darpa) project for an unmanned vessel that can shadow a manned sub throughout its patrol. Darpa recently chose Science Applications International Corp. to lead the design and construction of an operational prototype Anti-Submarine Warfare Continuous Trail Unmanned Vessel (Actuv). The aim is to demonstrate a non-stealthy autonomous vessel that can track a quiet diesel-electric submarine overtly for months, over thousands of kilometers, with minimal human input. At-sea testing is planned for mid-2015.

Actuv has a clean-sheet design, to take advantage of its crewless concept by relaxing normal warship requirements such as buoyancy reserve, dynamic stability and platform orientation. In addition to autonomy and reliability, a key goal of the program is to achieve “propulsive overmatch” and demonstrate “disproportionate” speed, endurance, maneuverability and sea-keeping to enable unconventional tactics in response to target behavior.

Actuv would not detect the submarine, but would relieve ASW forces of the task of keeping tabs on the boat once it has been picked up. It is intended to use acoustic, electro-optical, radar and lidar sensors to acquire and follow its sub targets through high seas and periods of lost communications, while navigating in compliance with international maritime regulations, autonomously avoiding other surface craft. With an unrefueled range of 6,200 km and an endurance of 80 days, the vessel will be under “sparse remote supervisory control” from the shore via beyond-line-of-sight data link.

But as advanced as Actuv and LDUUV may be in concept, they are years away from hitting the water, let alone becoming operational. For the time being, Europe and Israel appear to be well ahead in terms of making autonomous sea systems a reality.