1 9 PM . ▁An ▁improved ▁variant , ▁K - 5 M ▁or ▁R S - 2 US ▁in ▁P VO ▁service , ▁entered ▁production ▁in ▁ 1 9 5 9 , ▁matched ▁to ▁the ▁R P - 9 / R P - 9 U ▁( S ap fir ) ▁rad ar ▁of ▁the ▁Su k ho i ▁Su - 9 . ▁The ▁People ' s ▁Republic ▁of ▁China ▁developed ▁a ▁copy ▁under ▁the ▁design ation ▁PL - 1 , ▁for ▁use ▁by ▁their ▁J - 6 B ▁f igh ters . ▁ ▁The ▁difficulties ▁associated ▁with ▁beam - rid ing ▁guidance , ▁particularly ▁in ▁a ▁single - se at ▁f ighter ▁aircraft , ▁were ▁substantial , ▁making ▁the ▁' Al k ali ' ▁primarily ▁a ▁short - range ▁anti - b om ber ▁miss ile . ▁Ar ound ▁ 1 9 6 7 ▁the ▁K - 5 ▁was ▁replaced ▁by ▁the ▁K - 5 5 ▁( R - 5 5 ▁in ▁service ), ▁which ▁replaced ▁the ▁beam - rid ing ▁see ker ▁with ▁the ▁semi - active ▁rad ar ▁hom ing ▁or ▁inf ra red ▁seek ers ▁of ▁the ▁K - 1 3 ▁( AA - 2 ▁' At oll '). ▁The ▁weapon ▁was ▁ ▁heav ier ▁than ▁the ▁K - 5 , ▁but ▁had ▁a ▁smaller ▁ ▁war head . ▁The ▁K - 5 5 ▁remained ▁in ▁service ▁through ▁about ▁ 1 9 7 7 , ▁probably ▁being ▁retired ▁with ▁the ▁last ▁of ▁the ▁Su k ho i ▁Su - 9