The initially unarmed prototype, built at a cost of twenty million dollars, is a 132-foot -long trimaran. She is an unmanned self-piloting craft with twin screws, powered by two diesel engines with a top speed of. Her weight is 135 tons, including 40 tons of fuel, adequate for a 70-day cruise. Cruising range is "transoceanic," at fully fueled with 14,000 gallons of diesel, enough to "go from San Diego to Guam and back to Pearl Harbor on a tank of gas." Sea Hunter has a full load displacement of 145 tons and is intended to be operational through Sea State 5, waves up to high and winds up to, and survivable through Sea State 7, seas up to high. The trimaran hull provides increased stability without requiring a weighted keel, giving her a higher capacity for linear trajectories and better operations in shallow waters, though the greater width decreases maneuverability. A removable operator control station is installed during the testing period "for safety and backup" until it can be determined to reliably operate on her own. Operationally, computers will drive and control the ship, with a human always observing and taking charge if necessary in a concept called Sparse Supervisory Control, meaning a person is in control, but not "joy sticking" the vessel around. It can patrol without human guidance, using optical guidance and radar to avoid hitting obstacles or other watercraft. The ship has a host of non-standard features because of her lack of crew, including an internal layout that offers enough room for maintenance to be performed but not for any people to be permanently present. She is fitted with quicKutter shaft protection rope/line cutters from Quickwater Marine in Perth; these devices protect the vessel from damage caused by rope or net caught by the propellers, without affecting the vessels performance. The craft is expected to undergo two years of testing before being placed in service with the U.S. Navy. If tests are successful, future craft of this type may be armed and used for anti-submarine and counter-mine duties, operating at a small fraction of the cost of a destroyer, $15,000-$20,000 per day compared to $700,000 per day; it could operate with Littoral Combat Ships, becoming an extension of the LCS ASW module. Deputy US Defense SecretaryRobert Work said that if weapons are added to the ship, a human would always remotely make the decision to use lethal force. Following successful initial development, it was reported on 1 February 2018 that DARPA had handed development of Sea Hunter to the Office of Naval Research.
Sea trials
On 22 June 2016, Sea Hunter completed initial performance trials, meeting or surpassing all performance objectives for speed, maneuverability, stability, seakeeping, acceleration/deceleration, fuel consumption, and mechanical systems reliability in the open-ocean. Upcoming trials will include 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 will be adopted by the Office of Naval Research in summer 2017 for operational testing and evaluation for mine-countermeasure, EO/IR, and submarine detection capabilities. Plans for FY 2018 include adding intelligence, surveillance and reconnaissance and offensive anti-submarine payloads.
