and the TGS-33 IR seeker. Other candidates included active radar homing and dual IR/radar homing seekers. The final decision was made in favor of semi-active radar homing with an inertial initial stage. The homing device, designated MFBU-410 was developed by B.I.Ermakov under the supervision of Akopyan. The missile design was significantly altered later in 1972. The seeker and warhead were enlarged, the span of the control fins was reduced from 1100 mm to 900 mm. Further, the mounting system was revised to include new under-fuselage slipper pylons, akin to the Phoenix mount on the American F-14, and the missile was reoriented, so it mounted with the fins cruciform rather than diagonal; the fins on the mounting (dorsal) side were made to fold to the side, to lie flush against the belly of the carrying aircraft. Consequently, the missile launch method also needed to be changed. Rather than launching directly from the mounting pylon, the redesigned missile used drop-launch, with the missile being jettisoned from the pylon on launch, and its rocket motor igniting on a time-delay. A small run of one dummy (for launch system testing), 5 'programmed' (guidance and propulsion only, no warhead) and 8 fully functional trial missiles were built to the new design before the end of 1972. Of those 14, three were launched from the MiG-25P-10 testbed in 1973. Different warhead types (high explosive fragmentation and continuous-rod warhead) were evaluated, and tests of the radar and seeker systems were conducted on the LL-2. 1974 saw 11 more test launches from the MiG-25P-10, and the production of another 40 trial missiles. The first AKU-33 launchers and B-410 warheads were built. "Zaslon" tests continued at Akhtubinsk using the LL-2. The first flight of the future MiG-31 (aircraft No.831) took place on 16 September 1975, with 12 more flights by the end of the year. The MiG-25P-10 testbed launched 20 more test missiles before being sent for its launchers to be upgraded, and the first telemetric missile launches from the LL-2 were carried out that year. Development continued in 1976, including launches at PRM-2 parachute targets in April. Factory tests were completed in 1977 with 32 launches from the MiG-31 prototype, the first launch being against a MiG-17 drone on 26 March 1977). The guidance systems were improved during 1978, and the radar/missile combination performed a simultaneous launch at 4 targets in August. State trials started in March 1979