Soviet submarine K-27  K-27 was the only nuclear submarine of the Soviet Navy's Project 645. It was constructed by placing a pair of experimental VT-1 nuclear reactors that used a liquid-metal coolant (lead-bismuth eutectic) into the modified hull of a Project 627A (November-class) vessel. A unique NATO reporting name was not assigned. The keel of "K-27" was laid down on 15 June 1958 at Severodvinsk Shipyard No. 402. It was launched on 1 April 1962, and went into service as an experimental "attack submarine" on 30 October 1963. "K-27" was officially commissioned into the Soviet Northern Fleet on 7 September 1965. "K-27" was assigned to the 17th submarine division, headquartered at Gremikha). The nuclear reactors of "K-27" were troublesome from their first criticality, but the "K-27" was able to engage in test operations for about five years. On 24 May 1968, the power output of one of her reactors suddenly dropped sharply; radioactive gases were released into her engine room; and the radiation levels throughout "K-27" increased dangerously – by 1.5 grays per hour. This radiation consisted mostly of gamma rays and thermal neutrons, with some alpha radiation and beta radiation in addition – generated by the released radioactive gases such as xenon and krypton in her reactor compartment. The training of the crew by the Soviet Navy had been inadequate, and these sailors did not recognize that their nuclear reactor had suffered from extensive fuel element failures. By the time they gave up their attempts to repair the reactor at sea, nine of the crewmen had accumulated fatal radioactive exposures. About one-fifth of the reactor core had experienced inadequate cooling caused by uneven coolant flows. Hot spots in the reactor had ruptured, releasing nuclear fuel and nuclear fission products into the liquid-metal coolant, which circulated them throughout her reactor compartment. "K-27" was laid up in Gremikha Bay starting on 20 June 1968. The cooling-off of the reactors and various experimental projects were carried out aboard the submarine through 1973. These included the successful restarting of the starboard reactor up to 40% of maximal power production. Plans were considered to slice off the reactor compartment and replace it with a new one containing standard VM-A water-cooled reactors. The rebuilding or replacement of the nuclear reactor was considered to be too expensive, and also to be inappropriate because more modern nuclear submarines had already entered service in the Soviet Navy.