Question: who made a fully autonomous unmanned mini watercraft capable of independent operation underwater that differs from a submersible, which has more limited underwater capability?
Sentence (from "Submarine"): The noun "submarine" evolved as a shortened form of "submarine boat"; by naval tradition, submarines are usually referred to as "boats" rather than as "ships", regardless of their size ("boat" is usually reserved for seagoing vessels of relatively small size).
Relevant evidence: No