Sarov-class (B-90)

The B-90 Sarov, designated Project 20120 Sargan, is a Russian special purpose submarine. Designed by the Rubin Design Bureau during the 1980s, construction began in 1989 at the Krasnoye Sormovo Shipyard in Nizhniy Novgorod. Work stopped in 1998 due to a lack of funding following the dissolution of the Soviet Union. Following a revision of the project, construction resumed at the Sevmash Shipyard in Severodvinsk in 2003. The submarine was launched in December 2007 and entered service with the Russian Navy in August 2008. The existence of the vessel was first disclosed in 2007 when details were published on a local government website.

The design is based on the Kilo-class submarine but modified to incorporate a hybrid propulsion system. This system combines a conventional diesel-electric plant with a small auxiliary nuclear reactor. Rather than driving the propeller directly, the reactor generates electricity to recharge the battery system, which increases the vessel's underwater endurance. The low acoustic signature of the electric propulsion, combined with the extended range from the reactor, allows the vessel to operate in an intelligence-gathering role. To accommodate the auxiliary nuclear reactor section behind the sail and an escape capsule within the sail, the hull is longer than the baseline Kilo-class design.

Sarov operates with the Northern Fleet of the Russian Navy, serving as a technology demonstrator for testing weapons and military equipment, and as an intelligence collection vessel. In November 2016, United States defense officials reported that the submarine was involved in testing the Poseidon unmanned underwater vehicle. In February 2019, the Russian Ministry of Defence released video footage depicting the Poseidon vehicle being launched from a torpedo compartment aboard the submarine.