The R-33 (, NATO reporting name: AA-9 Amos) is a long-range air-to-air missile developed by Vympel. It is the primary armament of the MiG-31 interceptor, intended to attack large high-speed targets such as the SR-71 Blackbird, the B-1 Lancer bomber, and the B-52 Stratofortress. It uses a combination of semi-active radar homing for initial acquisition and mid-course updates, and inertial navigation to reach the target at extreme range. The Zaslon phased array radar of MiG-31 allows four missiles to be guided simultaneously at separate targets. The R-33 AAM remains in service with the CIS and Russian forces (See MiG-31 operators). Development The history of the R-33 missile is tightly bound to the story of its launcher, the MiG-31. The development of the modernized MiG-25, E-155MP, was authorized by a governmental decision of 24 May 1968. There was a competition for future missiles for the E-155MP. Izdeliye 410 by "Vympel" of A.L.Lyapin won, while the K-50 by PKPK of M.R.Bisnovat lost. The missile was assigned the development name K-33, continuing the series of K-13 and K-23 missiles. The development was headed by vice-chief designer V.V.Zhuravlev and leading designer Y.K.Zakharov. The R-33/MiG-31 missile/interceptor combination is similar to the earlier Bisnovat R-40/MiG-25 combination, although it is much more versatile and modern in that the MiG-25 was very heavily specialized for the interception of large supersonic targets such as the cancelled North American XB-70 Valkyrie bomber, and thus lacks maneuverability and is not suitable for air combat maneuvering. The MiG-31 is a much more versatile and capable aircraft and is still able to employ the older R-40. Two prototypes were built in 1968, featuring nose-mounted manoeuvring fins and intended for carriage on underwing pylons, similar to the Bisnovat R-40 on board the MiG-25. The draft project was completed in 1970 and progressed to testing using testbed aircraft. One of these was a converted early-production MiG-25 (aircraft P-10), and was used in 1972 for autonomous test launches from the upgraded APU-40 pylon. A MiG-21 (serial 76211524) was converted into the LL-21 testbed to test the missile seekers, while a Tu-104 jetliner (serial 42324) was converted into LL-104-518 (also known as LL-2) by NTK "Vzlet" to test the MFBU-410/"Zaslon" radar along with missile homing heads mounted on GVM-410 mockups. The space on board the passenger aircraft-based testbed allowed for the carriage of extensive diagnostic and support equipment. The K-33 was evaluated with the RGS-33 SARH seeker