The initially unarmed prototype, built at a cost of $20 million, is a 132-foot (40 meter)-long
trimaran (a central hull with two outriggers). It 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 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. 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. it could operate with
Littoral Combat Ships, becoming an extension of the LCS ASW module. 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 (ONR). ==Sea trials and operations==