The Bisnovat (later Molniya then Vympel) R-40 (NATO reporting name AA-6 'Acrid') is a long-range air-to-air missile developed in the 1960s by the Soviet Union specifically for the MiG-25P interceptor, but can also be carried by the later MiG-31.

The development of the Mach 3+ North American XB-70 Valkyrie threatened to make the entire interceptor and missile force of the Voyska PVO obsolete at one stroke, thanks to its incredible speed and altitude performance.

[5] To guarantee a kill at such high speeds in thin air, a large warhead was needed to have a sufficient blast effect.

Large control fins were required to give the missile enough maneuverability at high altitude.

Following the defection of Soviet Air Defense 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.