The 5,200 ton Sierras were the Russian response to the very successful American Lost Angeles class. The Sierras have eight torpedo tubes, four of them the larger 650mm (25.6 inch) type used to launch missiles or torpedoes. The Sierras were highly automated, requiring a crew of only 61 (about half found on a Los Angeles.) The Russians apparently believe that the Sierras are still competitive, and the other two boats of the class will probably be refurbished as well.
The newly affluent Russian navy (thanks to the rising price of oil) is spending some of that money to refurbish some of its better Cold War nuclear submarines. Many of these boats were allowed to fall apart during 1990s when the navy budget largely disappeared. One of four Sierra class boats have been refurbished and returned to service, after having been inactive since 1997. The Krab was the second of four Sierra class boats, the first of which entered service in 1984. The Krab did so in 1987. Two other Sierras entered service after the Cold War ended (in 1992 and 1993). Three more boats in this class were cancelled, as were many other subs and surface ships, as the Russian navy saw its budget cut by over 80 percent in the 1990s. This first of the Sierras was taken out of service in 1997, partly because it had been in a collision and the navy could not afford to repair it, and partly because the navy could not afford to operate the sub even if there had not been an accident.