GSF Explorer, formerly USNS Hughes Glomar Explorer (T-AG-193), was a deep-sea drillship platform built for Project Azorian, the secret 1974 effort by the Central Intelligence Agency's Special Activities Division to recover the Soviet submarine K-129.

The ship was built as Hughes Glomar Explorer in 1971 and 1972 by Sun Shipbuilding & Drydock Company for more than US$350 million (about $1.7 billion in 2024) at the direction of Howard Hughes for use by his company, Global Marine Development Inc. It began operation on 20 June 1974.

The ship's construction required a purpose-built crane ship, Sun 800, to lift its 630-ton gimbal into place.

Hughes told the media that the ship's purpose was to extract manganese nodules from the ocean floor. This marine geology cover story became surprisingly influential, causing many others to examine the idea.^{[citation needed]}

The Soviet diesel-electric submarine K-129 sank in the Pacific Ocean 1,560 miles (2,510 km) NW of Hawaii, on 8 March 1968. The USS Halibut identified the wreck site and the CIA crafted an elaborate and highly secret plan to recover the submarine for intelligence purposes. As K-129 had sunk in very deep water, at a depth of 16,500 feet (3 miles or 5 kilometres), a large ship was required for the recovery operation. Such a vessel would be detected easily by Soviet vessels, which might then interfere with the operation, so an elaborate cover story was developed. The CIA contacted Hughes, who agreed to help.

In 1974, the ship recovered a portion of K-129, but as the section was being lifted to the surface, a mechanical failure in the grapple caused two-thirds of the recovered section to break off. This lost section is said to have held many of the most-sought items, including the codebook and nuclear missiles. The recovered section held two nuclear-tipped torpedoes and some cryptographic machines, along with the bodies of six Soviet submariners, who were given a formal, filmed burial at sea.

The operation became public in February 1975 when the Los Angeles Times published a story about "Project Jennifer". Other news organizations, including the New York Times, added details. The CIA declined to either confirm or deny the reports, a tactic that became known as the Glomar response and subsequently used to confront all manner of journalistic and public inquiry, including Freedom of Information Act requests. The actual name, Project Azorian, became public only in 2010.

In Red Star Rogue (2005), Kenneth Sewell claims "Project Jennifer" recovered virtually all of K-129 from the ocean floor. Sewell states, "[D]espite an elaborate cover-up and the eventual claim that Project Jennifer had been a failure, most of K-129 and the remains of the crew were, in fact, raised from the bottom of the Pacific and brought into the Glomar Explorer".