In order to guarantee a kill at such high speeds and in the thin air, a large warhead was needed in order to have a sufficient blast effect.
Following the defection of IA-PVO pilot Viktor Belenko in 1976 and the compromising of the MiG-25P's systems and the associated R-40s, Vympel developed an improved version of the missile with a better infrared countermeasures (IRCM) resistance and more sensitive seekers.