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Tales For the Silent Service – The USN Anti-Submarine Class II Unmanned Surface Vessel USV

The Sea Hunter anti-submarine Class III unmanned surface vessel (USV) is an autonomous unmanned surface vehicle (USV) launched in 2016 as part of the DARPA, Defense Advanced Research Projects Agency, Anti-Submarine Warfare Continuous Trail Unmanned Vessel (ACTUV) program. It was christened on 7 April 2016 in Portland, Oregon where it was built at the Vigor Industrial’s Portland Swan Island shipyard, one of the largest and most capable shipyards on the West Coast. In addition to their marine teams in ship repair and shipbuilding, the Portland complex fab teams build bridges, aerospace components, and steel structures at the facility.
The Sea Hunter is classified as a Class III USV and designated as a Medium Displacement Unmanned Surface Vehicle (MDUSV) that is a prototype unmanned submarine tracking vessel having the ability to autonomously patrol the seas for months at a time, at a fraction of the current operational costs of manned vessels, and that could revolutionize US maritime operations and represents a new vision of naval surface warfare.

It is an unmanned self-piloting craft with twin propellers powered by two diesel engines having a top speed of 27 knots. And its displacement is 135 tons, including 40 tons of fuel, adequate for a 70-day cruise. Its cruising range is a transoceanic 10,000 nautical miles at 12 knots fully fueled with 14,000 gallons of diesel, sufficient to sail from San Diego to Guam and then on to Pearl Harbor on a single fueling. Sea Hunter has a full load displacement of 145 tons and is projected to be able to remain operational through Sea State 5, with waves up to 6.5 ft high and winds up to 21 knots, and survivable through Sea State 7, with seas up to 20 ft high. The craft is designed as a trimaran, a multi-hulled vessel comprising the main hull and two smaller outrigger hulls or ‘floats’ attached to it with lateral beams that provide increased stability without requiring a weighted keel, giving it a higher capacity for linear trajectories and effectual operations in shallow waters, though the greater width decreases its maneuverability somewhat. The future of such a craft is envisioned for it to be armed and utilized for anti-submarine and counter-mine duties, operating at a small fraction of the cost of a manned destroyer, $15,000-$20,000 per day compared to $700,000 per day; it could operate with Littoral Combat Ships, either of two classes of relatively small surface vessels designed for operations near shore, becoming an extension of the LCS ASW module (Littoral Combat Ship/Anti-Submarine Warfare). If weapons are added to the ship in the future, a human would always remotely decide to use lethal force. Following successful initial development, DARPA handed over the development of Sea Hunter to the Office of Naval Research (ONR) then it completed initial performance trials, meeting or surpassing all performance objectives for speed, maneuverability, stability, sea keeping, acceleration/deceleration, fuel consumption, and mechanical systems reliability in the open ocean. Additional trials included testing of sensors, the vessel’s autonomy suite, compliance with maritime collision regulations, and proof-of-concept demonstrations for a variety of U.S. Navy missions. The Sea Hunter MDUSV was adopted by the ONR in the summer of 2017 for operational testing and evaluation for mine-countermeasure, EO/IR, and submarine detection capabilities. Then in 2018 intelligence gathering, surveillance, and reconnaissance (ISR) systems, and offensive anti-submarine payloads were added.
According to DARPA, Sea Hunter could ultimately lead to a whole new class of ocean-going vessels and eradicate the need for larger manned warships, thereby totally transforming conventional submarine warfare. The vessel has the potential to traverse thousands of kilometers of open ocean for months at a time without a single crew member aboard and at dramatically reduced costs to operating surface ships and with zero risk of personnel. It represents a new vision of naval surface warfare that trades small numbers of very capable, high-value assets for large numbers of commoditized, simpler platforms that are more capable in the aggregate, according to DARPA’s Tactical Technology Office (TTO). The US military has long internally discussed the strategic importance of replacing ‘king’ and ‘queen’ pieces on the maritime chessboard with lots of ‘pawns’, and ACTUV is a first step toward doing exactly that.
Pending test results, Sea Hunter could enter service in a variety of roles. The drone’s stated purpose is to locate, track and engage submarines, primarily using a high frequency fixed sonar array, but Mine Countermeasures (MCM) testing suggests that MCM operations could be an option too. Both roles make good sense for an unmanned system such as Sea Hunter. A group of MDUSVs could more readily search a wider area for both hostile subs and mines and similar underwater hazards. The drone boats might also scout well ahead of manned ships for the enemy and get into close range of particularly high-value assets, such as aircraft carriers or amphibious assault ships.
Adversarial submarines pose a growing threat to the US Navy’s surface ships. And the emergence of Air-independent propulsion technology means diesel-electric submarines are quieter, and therefore more difficult for Allied forces sonar to detect. They can also remain submerged for significantly longer periods than their predecessors so smaller unmanned drone-type vessels such as Sea Hunter would also be more cost-effective than relying entirely on larger warships, aircraft, or aerial drones to search for and counter threats. Too, being able to endure up to 90 days at sea without a crew and with an estimated range of 10,000 nautical miles, fleets of unmanned surface drones could also provide 24/7 protection for inlets, harbors, and other sensitive naval locations, and also deliver missiles, torpedoes, and other supplies to vessels at sea.
Former US Deputy Defense Secretary Robert Work has said he believed USVs in general, and Sea Hunter in particular could revolutionize maritime operations. “This is an inflection point,” he said. “This is the first time we’ve ever had a totally robotic, trans-oceanic-capable ship.”
“I would like to see unmanned flotillas operating in the western Pacific and the Persian Gulf within five years,” he added, going on to emphasize that such fleets would always be under human control. “There’s no reason to be afraid of a ship like this.”
The US Navy clearly believes that unmanned ships have the potential to effectively track and engage enemy submarines for extended periods; plans already in the pipeline include equipping drones with anti-submarine weapons and additional sensor suites to gather visual and electronic intelligence. In addition to flexible mission capabilities, multiple autonomous fleets can potentially be operated by a single land-based crew, a budget-conscious alternative to conventional, personnel-heavy fleets.
The fact that China, Russia, and North Korea are seeking to expand their submarine fleets is another point in Sea Hunter’s favor. And a sister vessel, Sea Hunter II, has been ordered by the US Navy at an initial cost of $35.5m.
Captain Chris Sweeney, deputy director of Surface Warfare for Aegis and Ballistic Missile Defense, said that the service was considering forming an “experimental squadron” consisting of Sea Hunter, the first-in-class USS Zumwalt (DDG-1000) stealth destroyer, an Arleigh Burke-class guided-missile destroyer, and another littoral combat ship (LCS) for field evaluation. And Sea Hunter may even participate in real-world missions in the near future, beckoning forth a new era of naval operations dominated by fleets of drones operated by land-based crews. And as the Navy continues to experiment with its unmanned surface vehicle prototypes, the service planned to employ the Sea Hunter Medium USV in fleet exercises in the fiscal year 2021.
Speaking at a Navy League virtual event, Rear Adm. Casey Moton laid out his Fiscal Year 2021 priorities, or what he called “resolutions” for the new year, one of which is to continue prototyping unmanned systems and refine the service’s acquisition approach for the platforms.
“Our FY ’21 plans include the use of Sea Hunter in multiple fleet exercises, in tactical training events — with the Sea Hunter and the Overlord USVs we will exercise manned ship control on multiple USVs, test command and control, perform as part of the surface action groups, and train Navy sailors on these platforms,” Moton said, referring to the Pentagon’s Strategic Capabilities Office’s Overlord large USV program. However, little has been released concerning Sea Hunter’s operations during 2022 and beyond.