▁at ▁the ▁Soviet ▁Union . ▁ ▁Carter ▁and ▁Brown ▁worked ▁to ▁keep ▁the ▁balance ▁with ▁the ▁S ovi ets ▁in ▁strateg ic ▁weapons ▁by ▁impro ving ▁land - based ▁IC B M s , ▁by ▁equ ipping ▁strateg ic ▁bom bers ▁with ▁cru ise ▁miss iles ▁and ▁by ▁deploy ing ▁far ▁more ▁sub marine - launch ed ▁miss iles ▁t ipped ▁with ▁M IR V s , ▁or ▁multiple ▁war head s ▁that ▁could ▁hit ▁multiple ▁targets . ▁They ▁continued ▁development ▁of ▁the ▁M X ▁miss ile ▁and ▁modern ization ▁of ▁NAT O ' s ▁Long - Range ▁Theater ▁N uc lear ▁Force . ▁ ▁In ▁March ▁ 1 9 7 6 , ▁the ▁Soviet ▁Union ▁first ▁deployed ▁the ▁SS - 2 0 ▁Sab er ▁( also ▁known ▁as ▁the ▁R SD - 1 0 ) ▁in ▁its ▁European ▁territ ories , ▁a ▁mobile , ▁conce al able ▁intermediate - range ▁ball istic ▁miss ile ▁( IR B M ) ▁with ▁a ▁multiple ▁independently ▁target able ▁re entry ▁vehicle ▁( M IR V ) ▁containing ▁three ▁nuclear ▁ 1 5 0 - kil ot on ▁war head s . ▁The ▁SS - 2 0 ▁replaced ▁ag ing ▁Soviet ▁systems ▁of ▁the ▁SS - 4 ▁Sand al ▁and ▁SS - 5 ▁S ke an , ▁which ▁were ▁seen ▁to ▁pose ▁a ▁limited ▁threat ▁to ▁Western ▁Europe ▁due ▁to ▁their ▁poor ▁accuracy , ▁limited ▁payload ▁( one ▁war head ), ▁length y ▁prepar ation ▁time , ▁difficulty ▁in ▁being ▁conce aled , ▁and ▁imm ob