its contemporaries in terms of propulsion. The missile was fitted with a semi-active radar seeker 1SB4, designed by MNII Agat, which was able to track the target by Doppler frequency since the start. Later upgrades (3M9M3 missile) could do this before the start. Chief Designer of the seeker head was Yu.N. Vekhov, since 1960 – I.G. Akopyan. In 1977 a new version, the 3M9M1 (DoD designation SA-6B) was created with three missiles fitted onto a different chassis (the same as that of the 9K37 "Buk" (NATO reporting name "Gadfly" / DoD SA-11 ), the 2K12 effective replacement) with an integrated "Fire Dome" missile guidance radar. For comparisons between the 2K12, 9K37, see the 9K37 Buk entry. An earlier incremental upgrade saw the 2K12 missiles replaced with the 2K12E versions and this system was known as Kvadrat ("Квадрат", meaning square). This name was derived from the most common arrangement pattern of the military vehicles of the 2K12 complex, when the 1S91 radar is located at the center and 4x2P25 TELs at the vertices of a square around the radar. Comparison 1S91 radar SURN 1S91 vehicle included two radar station – a target acquisition and distribution radar 1S11 and a continuous wave illuminator 1S31, in addition to an IFF interrogator and an optical channel. While 1S31 antenna was installed on the upper section of the superstructure and the 1S11 on the lower, they could turn around independently. To make the height of the vehicle lower the central cylinder was able to hide inside the prime mover. The acquisition range of the radar was reported as for an F-4 Phantom II type of target. Total weight of the 1S91 vehicle with a crew of 4 was 20.3 tonnes and 2P25 vehicle with 3 missiles and a crew of 3 was 19.5 t. Additional radar The 2K12 can also be used at a regimental level, if used as such it can be accompanied by a number of additional radar systems for extended air search at longer range and lower altitude, to supplement the 1S91 "Straight Flush". These systems include the: P-12 "Spoon Rest", a VHF early warning radar (also used by the S-75 Dvina), with a range. P-40 "Long Track", an E band early warning radar (also used by the 2K11 Krug and 9K33 Osa), with a range. P-15 "Flat Face A", a UHF early warning radar (also used by the S-125 Neva, with