Missile RK-55 Granat (SS-N-21 Sampson)

Development of the RK-55 originated from the late 1960s "Ekho" study, which concluded that subsonic cruise missiles were more effective than supersonic designs. The system conducted its first flight in 1976 and entered service in 1984.

The RK-55 is a subsonic cruise missile designed for launch from ground-based transporter-erector-launchers or 533 mm submarine torpedo tubes. The submarine-launched variant is designated S-10 Granat. The missile utilizes a two-stage design, employing a solid-propellant rocket booster for launch and a turbofan engine for the cruise phase. Guidance is achieved via the Sprut inertial system combined with Terrain Contour Matching (TERCOM). Available payloads include a 200kt nuclear warhead, conventional unitary high explosive, or submunitions.

The system is operated by Russia and was previously utilized by the Soviet Union. Initial naval deployment was on Akula-class submarines, with the system later fitted to Sierra I/II, Victor III, and Yasen-class vessels. A specific configuration of the Yankee-class submarine replaced the standard missile compartment with additional torpedo tubes to accommodate land-attack variants. Following the implementation of the START I treaty, which restricted submarine-launched nuclear cruise missiles, these naval systems were transitioned to conventional warheads. Ground-based derivatives, designated 9M728 and 9M729, were reported as deployed in February 2017.