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 initially had a maximum dive depth of 6,500 feet (2,000 m); all Alvin-class personnel pressure hulls were originally designed for 6,000 ft (1,800 m), but subsequent testing allowed a higher rating.
From late September to early October 1990, over a course of 6 days, DSV-4 recovered the cargo door of United Airlines Flight 811 from the Pacific Ocean.
[3] As of 2019, the Naval Vessel Register shows DSV-4 was returned to active U.S. Navy service on September 30, 2002, in the custody of Woods Hole.
[4] Although an article in The New York Times from 1998 indicated that DSV-4 would be cannibalized to upgrade Alvin,[5] this appears to not have taken place since: 1) the US Navy Vessel Registry shows DSV-4 as an active vessel; 2) a photo from 2005 shows DSV-4 to still be intact with its personnel pressure sphere;[6] and 3) WHOI in its official history of Alvin does not discuss using DSV-4 parts during this timeframe.