The K-152 Nerpa (Russian: К-152 «Нерпа») is a 8,140-tonne (8,010-long-ton) Project 971 Shchuka-B (NATO: Akula II) type nuclear-powered attack submarine. Construction was started in 1991, but suspended due to lack of funding. K-152 Nerpa was launched in October 2008 and was planned to be leased to the Indian Navy in 2009 as the recommissioned INS Chakra. Nerpa is the Russian word for the baikal seal, and chakra is a Sanskrit word meaning disk, wheel, or energy vortex.
While K-152 Nerpa was undergoing sea trials in the Sea of Japan on 8 November 2008, an accident caused the deaths of some twenty sailors and injury to twenty-one others. A fire suppression system discharged freon gas in the bow of the sub, suffocating civilian specialists and navy crewmembers.