Soviet Air Defence Forces
Following the defection of Soviet Air Defence Forces 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. The upgraded missiles were designated with the suffix -D (for 'dorabotannye', "finalized"). Later -D1 versions were also developed.