The Akula class, Soviet designation Project 971 Shchuka-B is a series of fourth generation nuclear-powered attack submarines (SSNs) first deployed by the Soviet Navy in 1986. There are four sub-classes or flights of Shchuka-B, consisting of the original seven Project 971 boats, commissioned between 1984 and 1990; six Project 971Is, commissioned between 1991 and 2009; one Project 971U, commissioned in 1995; and one Project 971M, commissioned in 2001. The Russians call all of the submarines Shchuka-B, regardless of modifications.