Submarine-launched ballistic missile
The R-21 (Russian: Р-21; NATO: SS-N-5 'Sark/Serb'; GRAU: 4K55) was a submarine-launched ballistic missile in service with the Soviet Union 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 It replaced the R-11FM and R-13 (SS-N-4) on many Golf and Hotel-class submarines, and was in turn superseded by the R-27 (SS-N-6 'Serb') missile carried by Yankee-class submarines.
Development
Development of the R-15 and R-21 was initially assigned to Mikhail Yangel's Yuzhnoye Design Office (OKB-586) on 20 March 1958. The project was transferred to Viktor Makeyev'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.[2]
The 4th Research Institute had been conducting trials of underwater missile launch systems since 1955[2] with modified Scuds[citation needed] but the first successful launch was in 1960[2] and the first flight of a standard R-21 was in 1962.[2] Over the lifetime of the missile, 193 out of 228 launches were successful.[3]
The R-21 was probably the basis for the design of the North Korean No Dong (Rodong-1) missile.[4]
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.[2] This allowed missiles to be launched in a water depth of 40-60m.[5] The propulsion system used an IRFNA-Inhibited red fuming nitric acid-amine fuel, AK-27I/TG-02. The AK-27I oxidizer was a mixture of 73% nitric acid, 27% nitrogen tetroxide, and an iodine inhibitory passivant.[6] The fuel was originally used in the Wasserfall rocket under the name TONKA-250 and consisted of 50% triethylamine and 50% xylidine.[6] This gave the R-21 a range of 1,400 km (760 nmi), double that of first-generation sub-launched missiles.[5] The Naval Institute Guide suggests that the range was initially 1300 km, and extended to 1650 km later in the life of the missile.[1] There was a single warhead of approximately 800 kilotons.[1]
Variants
- R-21 (4K55) - original design
- R-21A (4K55A) - subsequent modification[2]
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 'Sark' like the SS-N-4 first carried by the Golf submarines,[7] but some variants were assigned the name 'Serb' normally used for the SS-N-6.[1] Jane's uses 'Sark'.[2]
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,[2] between 1963 and 1967.[5] They were succeeded from 1967 by Yankee-class submarines carrying 2400 km-range R-27 (SS-N-6 'Serb') missiles.[8] Seven of the eight Hotel I (Project 658) subs were upgraded to Hotel II (Project 658M) standard, which were retired by 1991.[9]
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