DSV Sea Cliff

DSV-4 (formerly known as Sea Cliff) is a 25-ton, manned 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), Alvin (DSV-2). The Alvin-class DSVs were designed to replace older DSVs, such as the less-maneuverable Trieste-class bathyscaphes. Sea Cliff was built by Electric Boat in Groton, Connecticut for the U.S. Navy and was completed in December 1968. It spent much of its service life on loan to the Woods Hole Oceanographic Institution.

DSV-4 originally had a maximum dive depth of 6,500 feet (2,000 m), as all Alvin-class DSVs did at first. It was redesigned to dive to 20,000 feet (6,100 m) and refitted in 1984. With the refit of DSV-4, the bathyscaphe DSV-1 (formerly known as Trieste II) was retired from service.

In 1985 the Sea Cliff made a record dive for this vessel type by diving 20,000 feet off Guatemala's Pacific Coast.[1] The crew of the dive consisted of pilot Lt. Alan Mason and co-pilot Chief Petty Officer David Atchinson.

DSV-4 has a plug hatch 2 feet (0.61 m) in diameter, held in place mechanically with hatch dogs and, while submerged, by the pressure of the water above it. DSV-4 can dive 5,000 feet (1,524 meters) deeper than the famed Alvin; however, the Super Alvin-class replacement for DSV-2 is designed to dive to 22,000 feet (6,705 meters).

Sea Cliff was retired from active service in 1998 and subsequently given to Woods Hole Oceanographic Institution (WHOI).[2] The Naval Vessel Register shows DSV-4 was returned to active U.S Navy service on 30 September 2002 in the custody of WHOI,[3] but an article in The New York Times indicates that it was cannibalized for parts for Alvin.[4]