SS-N-21

RK-55 Relief (NATO reporting name: SSC-X-4 'Slingshot') S-10 Granat (SS-N-21 'Sampson')
RK-55 Transporter-Erector-Launcher
Type	surface/sub-launched nuclear cruise missile
Place of origin	Soviet Union
Service history
In service	since 1984
Used by	Soviet Union / Russia
Production history
Designer	L. V. Lyulev
Designed	1975
Manufacturer	Novator
Produced	1976
Specifications
Weight	1,700 kg (3,750 lb)
Length	809 cm (26 ft 7 in)
Diameter	51 cm (20.1 in)
Warhead	Conventional Nuclear
Blast yield	Nuclear 200kt
Engine	Solid-propellant rocket booster + R-95-300 turbofan 450 kgf
Wingspan	310 cm (122.0 in)
Operational range	3,000 km (1,600 nmi)
Speed	720 km/h (447.4 mph)
Guidance system	Sprut inertial guidance plus TERCOM
Launch platform	Akula-class submarine, Sierra II, Victor III, Yankee Notch, Yasen-class submarine, TEL

The Novator RK-55 Relief (Russian: РК-55 Рельеф 'Relief'; NATO: SSC-X-4 'Slingshot'; GRAU: 3K12) is a Soviet land-based cruise missile with a nuclear warhead. It was about to enter service in 1987 when such weapons were banned under the Intermediate-Range Nuclear Forces Treaty. A version launched from submarine torpedo tubes, the S-10 Granat (SS-N-21 'Sampson'; GRAU: 3K10), has apparently been converted to carry conventional warheads and continues in service to this day. Russian Federation deployed SSC-X-8 in March 14 2017.

The RK-55 is very similar to the air-launched Kh-55 (AS-15 'Kent') but the Kh-55 has a drop-down turbofan engine and was designed by MKB Raduga. Both have formed the basis of post-Cold-War missiles, in particular the Sizzler which has a supersonic approach phase.

In the late 1960s, the "Ekho" study conducted by the GosNIIAS institute concluded that it would be more effective to deploy lots of small, subsonic cruise missiles than the much more expensive supersonic missiles then in favour. In 1971 Raduga began working on the air-launched Kh-55, which first flew in 1976. That same year, RK-55 first flew.NPO Novator would work on the submarine- and ground-launched versions. In 1993 Novator exhibited the Sizzler series weapons, which appears to be based on the RK-55. It is a two-stage design, which goes supersonic during its final approach to the target.

Six RK-55 missiles are carried on an eight-wheeled transporter-erector-launcher (TEL) based on the MAZ 543 launcher of the R-17 (SS-1 'Scud B').

The S-10 is launched through 533 mm torpedo tubes.

Fewer than 100 SS-N-21s had been deployed by the end of 1988. The new Akula-class submarine, launched in September 1986, was the first class to receive the new missile. It was later fitted to the Sierra I/II class and eight Victor III's and the new Yasen-class submarines.