The R-21 (;

NATO The North Atlantic Treaty Organization (NATO ; , OTAN), also called the North Atlantic Alliance, is an intergovernmental organization, intergovernmental Transnationalism, transnational military alliance of 32 Member states of NATO, member s ...

: SS-N-5 'Sark/Serb';

GRAU The Main Missile and Artillery Directorate of the Ministry of Defense of the Russian Federation (), commonly referred to by its transliterated acronym GRAU (), is a department of the Russian Ministry of Defense. It is subordinate to the Chief of ...

: 4K55) was a

submarine-launched ballistic missile A submarine-launched ballistic missile (SLBM) is a ballistic missile capable of being launched from Ballistic missile submarine, submarines. Modern variants usually deliver multiple independently targetable reentry vehicles (MIRVs), each of which ...

in service with the

Soviet Union The Union of Soviet Socialist Republics. (USSR), commonly known as the Soviet Union, was a List of former transcontinental countries#Since 1700, transcontinental country that spanned much of Eurasia from 1922 until Dissolution of the Soviet ...

between 1963 and 1989. It was the first Soviet nuclear missile that could be launched from a submerged submarine, and also had twice the range of earlier missiles. It replaced the

R-11FM The R-11 Zemlya (), GRAU index 8A61 was a Soviet Union, Soviet tactical ballistic missile. It is also known by its NATO reporting name SS-1b Scud-A. It was the first of several similar Soviet missiles to be given the reporting name Scud. Variant R ...

and R-13 (SS-N-4) on many

Golf Golf is a club-and-ball sport in which players use various Golf club, clubs to hit a Golf ball, ball into a series of holes on a golf course, course in as few strokes as possible. Golf, unlike most ball games, cannot and does not use a standa ...

and

Hotel-class submarine The Hotel class is the general NATO reporting name, NATO classification for a type of nuclear marine propulsion, nuclear-powered ballistic missile submarine that was launched by the Soviet Union around 1959. The Soviet designation was Project 658. ...

s, and was in turn superseded by the R-27 (SS-N-6 'Serb') missile carried by

Yankee-class submarine The ''Yankee'' class, List of ships of Russia by project number, Soviet designations Project 667A ''Navaga'' (navaga) and Project 667AU ''Nalim'' (burbot) for the Initial operating capability, basic ''Yankee''-I, were a family of Nuclear propuls ...

Development

Development of the R-15 and R-21 was initially assigned to

Mikhail Yangel Mikhail Kuzmich Yangel (; 7 November 1911 – 25 October 1971), was a Soviet people, Soviet engineer born in Irkutsk who was the leading designer in the missile program of the former Soviet Union. Biography Yangel was the grandson of a Russ ...

Yuzhnoye Design Office The ''Pivdenne'' Design Office (), located in Dnipro, Ukraine, is a designer of satellites and rockets, and formerly of Soviet intercontinental ballistic missiles (ICBMs), established by Mikhail Yangel. During the Soviet era, the bureau's OKB de ...

(OKB-586) on 20 March 1958. The project was transferred to

Viktor Makeyev Viktor Petrovich Makeyev (also Makeev; ; 25 October 1924 – 25 October 1985) was a Soviet engineer in the Soviet space program who was also a central and founding figure in development of Submarine-launched ballistic missile (SLBM) for the S ...

's SKB-385 on 17 March 1959. It was intended for the ''Golf''-class submarines (Project 629B); the complete missile system was called the D-4 weapon complex. The 4th Research Institute had been conducting trials of underwater missile launch systems since 1955 with modified Scuds but the first successful launch was in 1960 and the first flight of a standard R-21 was in 1962. Over the lifetime of the missile, 193 out of 228 launches were successful. The R-21 was probably the basis for the design of the North Korean

Hwasong-7 The Hwasong-7} () is a single-stage, mobile liquid propellant medium-range ballistic missile developed by North Korea. Developed in the mid-1980s, it is a scaled-up adaptation of the Soviet R-17 Elbrus missiles, more commonly known by its NATO rep ...

(No Dong) missile.

Design

Unlike Western designs, the R-21 used a cold launch solid rocket to eject the missile from the flooded launch tube before the main motor ignited. This allowed missiles to be launched in a water depth of 40-60 m. The propulsion system used an Inhibited red fuming nitric acid-amine propellants combination, ''AK-27I/TG-02''. The AK-27I oxidizer was a mixture of 73% nitric acid, 27%

nitrogen tetroxide Dinitrogen tetroxide, commonly referred to as nitrogen tetroxide (NTO), and occasionally (usually among ex-USSR/Russian rocket engineers) as amyl, is the chemical compound N2O4. It is a useful reagent in chemical synthesis. It forms an equilibrium ...

, and an

iodine Iodine is a chemical element; it has symbol I and atomic number 53. The heaviest of the stable halogens, it exists at standard conditions as a semi-lustrous, non-metallic solid that melts to form a deep violet liquid at , and boils to a vi ...

inhibitory passivant. The fuel was originally used in the

Wasserfall The ("Waterfall remote-controlled anti-aircraft rocket") was a German guided supersonic surface-to-air missile project of World War II. Development was not completed before the end of the war and it was not used operationally. The system was ...

rocket under the name

TONKA-250 Tonka is the name given to a family of German-designed rocket propellants first used under the name R-Stoff in the Wasserfall missile. Tonka propellants were later used in the Soviet Union, most commonly the TG-02 formulation, for example in the en ...

and consisted of 50%

triethylamine Triethylamine is the chemical compound with the formula N(CH2CH3)3, commonly abbreviated Et3N. Like triethanolamine and the tetraethylammonium ion, it is often abbreviated TEA. It is a colourless volatile liquid with a strong fishy odor remini ...

and 50%

xylidine Xylidine can refer to any of the six isomers of xylene amine, or any mixture of them. The chemical formula of xylidines is C8H11N or, more descriptively, (CH3)2C6H3NH2. The CAS number for the isomer mixture is 1300-73-8. They are colorless solids ...

. This gave the R-21 a range of , double that of first-generation sub-launched missiles. The Naval Institute Guide suggests that the range was initially 1300 km, and extended to 1650 km later in the life of the missile. There was a single warhead of approximately 800 kilotons.

Variants

* R-21 (4K55) - original design * R-21A (4K55A) - subsequent modification There was some confusion about the SS-N-4/5/6 series of missiles in the West, the SS-N-5 is normally given the

NATO reporting name NATO uses a system of code names, called reporting names, to denote military aircraft and other equipment used by post-Soviet states, former Warsaw Pact countries, China, and other countries. The system assists military communications by providi ...

'Sark' like the SS-N-4 first carried by the Golf submarines, but some variants were assigned the name 'Serb' normally used for the SS-N-6. Jane's uses 'Sark'.

Operational history

The missiles replaced first-generation R-11FM and R-13 missiles on some Golf (Project 629) and Hotel (Project 658) class SSBNs, with three missiles per submarine, between 1963 and 1967. They were succeeded from 1967 by

s carrying 2400 km-range R-27 (SS-N-6 'Serb') missiles. Seven of the eight Hotel I (Project 658) subs were upgraded to Hotel II (Project 658M) standard, which were retired by 1991.Bukharin (2004) p292

Operators

; * North Korean Navy ; *

Soviet Navy The Soviet Navy was the naval warfare Military, uniform service branch of the Soviet Armed Forces. Often referred to as the Red Fleet, the Soviet Navy made up a large part of the Soviet Union's strategic planning in the event of a conflict with t ...

References

External links

R-21 / SS-N-5 SERB
GlobalSecurity.org has many historical details
www.aviation.ru
R-21 {{Use dmy dates, date=June 2017 R-021 Cold War missiles of the Soviet Union Makeyev Rocket Design Bureau Military equipment introduced in the 1960s