▁M X , ▁one ▁Lo AD S ▁and ▁ 2 1 ▁de co ys . ▁At ▁first ▁glance ▁it ▁might ▁appear ▁that ▁only ▁one ▁additional ▁enemy ▁war head ▁would ▁be ▁needed , ▁using ▁up ▁the ▁Lo AD S ▁inter ceptor . ▁However , ▁only ▁the ▁def ender ▁knew ▁where ▁the ▁M X ▁was , ▁and ▁Lo AD S ▁would ▁only ▁fire ▁at ▁the ▁single ▁war head ▁seen ▁approaching ▁that ▁shelter . ▁That ▁meant ▁that ▁the ▁M X ▁would ▁almost ▁definitely ▁surv ive ▁a ▁single ▁war head ▁attack . ▁In ▁order ▁to ▁be ▁sure ▁the ▁M X ▁was ▁hit , ▁the ▁S ovi ets ▁would ▁have ▁to ▁attack ▁every ▁shelter ▁with ▁two ▁war head s , ▁assuming ▁one ▁would ▁be ▁lost ▁to ▁the ▁Lo AD S . ▁For ▁a ▁typical ▁ 2 3 - site ▁M PS , ▁ 4 6 ▁war head s ▁would ▁be ▁needed , ▁so ▁if ▁Lo AD S ▁remained ▁within ▁the ▁ 1 0 0 - inter ceptor ▁limit ▁of ▁the ▁AB M ▁treat y , ▁ 4 , 6 0 0 ▁war head s ▁would ▁be ▁needed ▁to ▁attack ▁just ▁one - half ▁of ▁the ▁ 2 0 0 - strong ▁M X ▁fleet , ▁leaving ▁ 1 0 0 ▁miss iles ▁and ▁ 1 , 0 0 0 ▁war head s ▁in ▁the ▁US ▁counter att ack . ▁An ▁attack ▁against ▁the ▁entire ▁fleet ▁would ▁require ▁them ▁to ▁break ▁the ▁Str ateg ic ▁Ar ms ▁Lim itation ▁Tal ks ▁limits ▁on ▁the ▁number ▁of ▁off ensive ▁war