▁question able ▁security ▁of ▁the ▁M X ▁once ▁again ▁became ▁an ▁issue , ▁Re agan ▁briefly ▁ent ert ained ▁an ▁even ▁shorter - range ▁system ▁known ▁as ▁Sw arm jet , ▁before ▁the ▁entire ▁M X ▁program ▁was ▁sever ely ▁cur ta iled ▁with ▁the ▁ending ▁of ▁the ▁Cold ▁War . ▁ ▁Background ▁ ▁IC B M ▁vulner ability ▁ ▁Early ▁IC B M s ▁had ▁accuracy ▁on ▁the ▁order ▁of ▁, ▁which ▁made ▁them ▁useful ▁against ▁only ▁the ▁largest ▁targets . ▁Through ▁the ▁ 1 9 6 0 s ▁this ▁was ▁progress ively ▁improved , ▁and ▁the ▁US ▁estimated ▁that ▁the ▁S ovi ets ▁would ▁have ▁" subst ant ial " ▁cap ability ▁of ▁directly ▁attack ing ▁US ▁miss ile ▁sil os ▁by ▁the ▁ 1 9 8 0 ▁time ▁frame . ▁ ▁This ▁led ▁to ▁a ▁worry ing ▁scenario ▁coming ▁to ▁domin ate ▁US ▁strateg ic ▁thinking ▁through ▁the ▁ 1 9 7 0 s ▁and ▁ 8 0 s . ▁If ▁the ▁S ovi ets ▁launched ▁a ▁s ne ak ▁attack ▁on ▁the ▁US ▁using ▁only ▁a ▁portion ▁of ▁their ▁miss ile ▁fleet , ▁about ▁, ▁aim ed ▁sole ly ▁at ▁US ▁sil os ▁and ▁air b ases , ▁they ▁could ▁hope ▁to ▁destroy ▁as ▁much ▁as ▁ 9 0 % ▁of ▁the ▁US ' s ▁fleet . ▁This ▁attack ▁would ▁not ▁kill ▁many ▁civ ili ans , ▁and ▁leave ▁the ▁US ▁with ▁only ▁a ▁few ▁IC B M s ▁and ▁bom bers , ▁along ▁with ▁the ▁US ▁Navy '