DSV Sea Cliff
DSV-4 (formerly known as Sea Cliff) is a 25-ton, crewed deep-ocean research submersible owned by the United States Navy, now known only by its hull number, not by its former name. DSV-4 is an Alvin-class deep submergence vehicle (DSV), a sister ship to Turtle (DSV-3) and Alvin (DSV-2).