'pace') was a mobile intercontinental ballistic missile developed by the Soviet Union during the Cold War.

[citation needed] Its innovative concept and design were created by Alexander Nadiradze.

The RSD-10 Pioneer and succeeding missile complexes relied on the RT-21 base concept and were used by Nadiradze for many of his later projects.

The program became mired in a series of treaty complications, including questions regarding its use of theatre missile launchers.

Its maximum period of storage on a launcher was 5 years, and preparation time for launch was 40 minutes.