From 1968 to 30 November 2005, the was the main Atlantic operational force of the fleet. The Museum of the Air Forces of the Northern Fleet was opened on 20 August 1976, in the closed settlement of Safonovo, Murmansk Oblast. Aircraft carriers began entering service with the Fleet in the 1970s. The lead unit of the Kiev class of heavy aircraft-carrying cruisers, "Kiev", became operational in 1977, and "Admiral Gorshkov" was commissioned in 1987. Large nuclear-powered missile-carrying cruisers, the and "Kalinin", also entered service from 1980. Fortification of the southern reaches of the Barents Sea during the 1980s marked a Soviet naval strategy shift to an emphasis on bastion defense. Russia has continued to employ that strategy.