K-129 (Russian: К–129) was a Project 629A (Russian: проект 629А Projekt 629A, NATO reporting name Golf II–class) diesel-electric-powered ballistic-missile submarine that served in the Pacific Fleet of the Soviet Navy–one of six Project 629 strategic ballistic-missile submarines assigned to the 15th Submarine Squadron based at Rybachiy Naval Base near Petropavlovsk, commanded by Rear Admiral Rudolf Golosov.

The K-129's commander was Captain First Rank Vladimir I. Kobzar, and she carried the hull number 722 on her final deployment, during which she sank on 8 March 1968. This was one of four mysterious submarine disappearances in 1968, the others being the Israeli submarine INS Dakar, the French submarine Minerve, and the American submarine USS Scorpion.

After nearly two weeks of silence during her patrol in the Pacific Ocean, the Soviet Navy officials became concerned about her status and reportedly deployed large numbers of military aircraft and ships to search for the vessel, but no sign or wreckage was found. With the U.S. Navy observing the Soviet efforts, the Americans also began searching, ultimately determining the exact coordinates of the wreck utilizing underwater acoustic data in August 1968, hundreds of miles away from the Soviet search efforts.

In 1974, the United States attempted to recover the submarine in a secretive Cold War–era effort named Project Azorian. Only a part of the submarine was recovered from its position 4.9 km (16,000 ft) below the surface, making this the deepest attempt to raise a ship. The cover story was that the salvage vessel was engaged in commercial manganese nodule mining.

Launch and operations

The keel of K-129 was laid down on 15 March 1958 at Komsomolsk-on-Amur Shipyard No. 132.

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 United States Central Intelligence Agency's Special Activities Division to recover the Soviet submarine K-129.

Construction

The ship was built as Hughes Glomar Explorer in 1971 and 1972 by Sun Shipbuilding and Drydock Co. for more than US$350 million (about $1.7 billion in 2023) 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.

Project Azorian

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.