Mike-class

Project 685 Plavnik, designated by NATO as the Mike class, was a Soviet nuclear-powered attack submarine. Developed by the Rubin Design Bureau, the project originated from a 1966 requirement for a vessel capable of carrying both torpedoes and cruise missiles with conventional or nuclear warheads. Design work was completed in 1974, and the keel of the sole vessel of the class, K-278, was laid at the Sevmash shipyard on 22 April 1978. The vessel was launched in June 1983 and commissioned on 28 December 1983.

The submarine was constructed with a double hull, utilizing titanium for the internal pressure hull to facilitate deep-submergence operations. The structure was divided into seven compartments, with the second and third compartments reinforced by bulkheads to serve as a safety zone. An emergency escape capsule was integrated into the fin to permit crew evacuation from depth. Propulsion was provided by an OK-650 b-3 pressurized-water reactor. The design incorporated automated systems, with a standard complement of 64 personnel consisting of 30 officers, 22 warrant officers, and 12 petty officers and enlisted men.

K-278 was utilized to evaluate technology for fourth-generation Soviet nuclear submarines while maintained for active combat deployment. In August 1984, the submarine reached a depth of 1,020 meters in the Norwegian Sea. In October 1988, the vessel received the name Komsomolets.

On 7 April 1989, during its third operational patrol, the submarine suffered a short circuit that initiated a fire in an engineering compartment. At the time, the vessel was submerged at a depth of 335 meters in the Barents Sea. The fire spread through bulkhead cable penetrations, leading to a loss of propulsion and electrical failures. Following an emergency ballast blow, the vessel surfaced but eventually sank after several hours. Of the 69 personnel on board, 42 died and 27 survived.

The wreck remains on the seabed at a depth of approximately 1,700 meters. The hull contains the nuclear reactor and two torpedoes equipped with nuclear warheads. Expeditions conducted between 1994 and 1996 applied sealants to fractures in the first compartment and covered the nuclear warheads. Annual monitoring by Norwegian and Russian agencies has identified localized caesium-137 emissions near the wreck, though current levels are not classified as a threat to the environment.