This is a model of Russian engagement radar Grave Stone/Flap Lid, used in S-400/S-300 (SA-21/SA-10 SA-20) SAM systems, mounted on 40B6M mast. Although associated with different SAM systems, Grave Stone (from SA-21) and Flap Lid (SA-10 SA-20) look almost identically, having different chassis as main distinctive sign. Sometime, they both can be mounted on optional 40V6M mobile mast. This allow improve the radars range, also as sometime it is neccessary because of surface conditions, like hills and/or forest of high trees. The 40V6M mobile mast use as optional equipment for various types of radars from S-300/S-400 SAM systems. This assets can be used like Grave Stone (S-400) or Flap Lid (S-300) radars. They look absolutely identically when mounted on the mast.