Project 685 Plavnik
Mike class

The Project 685 was an advanced submarine developed to test advanced submarine technologies. The submarine could carry a mix of torpedoes and cruise missiles with conventional or nuclear warheads. During trial operation of the K-278 for the first time in world practice for combat submarines reached an unsurpassed depth of –1020 m to date, which made it, in combination with the available weapons and technical ideas of the 21st century incorporated into the design, a terrible means to destroy any enemy surface and submarines.

The design was initially developed in the 1960s, but the first unit was not laid down at Severodvinsk until 22 April 1978. The submarine K-278 Komsomolets ["member of the Young Communist League"] was launched on 09 May 1983 and commissioned in late 1984. The submarine Komsomolets was built as an experimental vessel, and was the only one of its class to enter service. The construction of one additional submarine was reported started in Severodvinsk, but work was halted prior to its completion.

The hull was of double-hull configuration, divided into seven compartments: Torpedo room, Accommodations, Control room, Reactor compartment, Electrical motors, Turbines and Auxiliary mechanisms. The inner pressure hull was titanium, light and strong, making her the world's deepest diving submarine, and her operating depth below 3,000 feet was far below that of the best American submariness. A personnel rescue sphere was fitted in the sail to enable the crew to escape in the event of an underwater emergency. According to Western intelligence estimates, the Mike was powered by a pair of liquid-metal/lead-bismuth reactors, although the Soviet Union subsequently disclosed that the submarine used a single pressurized-water reactor of conventional design. This resulted in subsequent lower estimates for the boat's maximum speed.

On 07 April 1989, while the Komsomolets was submerged at a depth of 500-1,250 feet a fire erupted in the aft compartment when a high-pressure air line connecting to main ballast tanks allowing the submarine to control its depth bursts a seal. A spray of oil hit a hot surface, and a flash fire began which soon The fire spread through cableways despite closed hatches. The emergency system to protect the nuclear reactors from overload kicked in, and the propeller shaft stopped. Within minutes electrical problems were reported all over the submarine, and many security systems failed. The boat managed to surface eleven minutes after discovery of the fire, but the rupture in the main compressed air system fed the fire further. The crew fought the fire for several hours before the submarine flooded and sank. As she sank, the commanding officer and four others entered the escape pod, but it was partially flooded and filled with toxic gas, and only one of the five survived the ascent to the surface. Small rafts were dropped from the rescue aircraft, but there were not enough for the 50 men in the water. Of the 69 crew members, 42 were killed in the accident, most dying in the water of hypothermia [at 36° F the water was cold enough to kill them in 15 minutes].

The Komsomolets sank 180 km southeast of Bear Island off the coast of Norway in 1,500-1,700 meters of water. The Komsomolets was carrying two nuclear torpedoes [along with eight conventional torpedoes] when she sank. Two investigations, one by a state commission and another conducted independently, failed to fully account for the magnitude of the accident, though the independent commission suggested that Komsomolets had construction flaws. Others have claimed that the crew was not properly trained to operate the submarine's equipment. The Norwegians claimed they could have reached the scene by air or surface two hours before the submarine sank.

The site of the accident is one of the richest fishing areas in the world, and the possible leakage of radioactive material could jeopardize the local fisheries, valued at billions of dollars annually. Two months after the sinking, the oceanographic rescue ship Akademik Mstislav Keldysh using submersibles found Komsomolets a mile down. In August of 1991, Keldysh returned to the scene and examination of the wreck in May 1992 revealed cracks along the entire length of the titanium hull, some of which were of 30-40 centimeters wide, as well as possible breaches in the primary coolant circuit that could permit fission products to leach out into sea water. As of early 1993 Russian officials maintained that leaks were "insignificant" and posed no threat to the environment. Results of the August 1993 survey suggested that waters at the site were not mixing vertically, and thus the sea life in the area was not being rapidly contaminated. The 1993 survey also revealed a hole over 20 feet wide blown in the forward torpedo compartment.

Several underwater submersible missions to the site revealed that sea water was corroding the casings of the warheads and the hull of the submarine, a process accelerated by the rapidly shifting currents. Concern was expressed that radiation could leak from missiles and contaminate a large area because of the aperiodically high (up to 1.5 m/sec) currents in the area. The Radioactivity and Environmental Security in the Oceans Conference at Woods Hole Oceanographic Institution on June 7-9, 1993 considered the environmental monitoring program on the Komsomolets submarine. An expedition during the summer of 1994 revealed some plutonium leakage from one of the sub's two nuclear-tipped torpedoes. The expedition was successful in sealing some of the holes in the submarine's hull.

The cost of raising the submarine was estimated at about of $1 billion, which would entail the hazard that the submarine hull might not remain intact during the operation. An alternative plan was to encase the submarine by hermetically sealing it with a jelly-like material. On 24 June 1995 work began on sealing parts of the hull, and the objective was achieved at the end of July 1996. The hull was said to be safe for at least 20 to 30 more years. As of the late 1990s examinations of the area where the sub sank measured only small leaks of radioactivity from the wreck.

A joint Norwegian-Russian team of scientists said 10 July 2019 that a remote-controlled mini-sub had taken samples near the wreckage and found the level of radioactivity at the site was up to 100,000 times higher than normal. The remotely operated vehicle called Aegir 6000 examines the wreck of the Soviet nuclear submarine Komsomolets, southwest of Bear Island in the Norwegian Arctic, Norway. While Russia and Norway have monitored radiation levels annually since the sub sank, it is the first time a submersible was used to conduct the tests. "This is, of course, a higher level than we would usually measure out at sea, but the levels we have found now are not alarming," said expedition leader Hilde Elise Heldal of the Norwegian Institute of Marine Research. Radioactivity levels "thin out" quickly at these depths and there are few fish in the area, she said.