▁more ▁than ▁enough ▁miss iles ▁to ▁over wh elm ▁any ▁American ▁defense ), ▁but ▁rather ▁against ▁the ▁potential ▁nuclear ▁threat ▁of ▁the ▁People ' s ▁Republic ▁of ▁China . ▁ ▁In ▁the ▁meant ime , ▁a ▁public ▁debate ▁over ▁the ▁mer it ▁of ▁AB M s ▁began . ▁D iff icult ies ▁that ▁had ▁already ▁made ▁an ▁AB M ▁system ▁question able ▁for ▁def ending ▁against ▁an ▁all - out ▁attack . ▁One ▁problem ▁was ▁the ▁Fra ction al ▁Or b ital ▁Bomb ard ment ▁System ▁( FO BS ) ▁that ▁would ▁give ▁little ▁warning ▁to ▁the ▁defense . ▁Another ▁problem ▁was ▁high ▁alt itude ▁E MP ▁( wh ether ▁from ▁off ensive ▁or ▁def ensive ▁nuclear ▁war head s ) ▁which ▁could ▁deg rade ▁def ensive ▁rad ar ▁systems . ▁ ▁When ▁this ▁proved ▁in fe as ible ▁for ▁economic ▁reasons , ▁a ▁much ▁smaller ▁deployment ▁using ▁the ▁same ▁systems ▁was ▁proposed , ▁namely ▁Saf egu ard ▁( des cribed ▁later ). ▁ ▁Def ense ▁against ▁M IR V s ▁ ▁AB M ▁systems ▁were ▁developed ▁initially ▁to ▁counter ▁single ▁war head s ▁launched ▁from ▁large ▁Inter cont inental ▁ball istic ▁miss iles ▁( IC B M s ). ▁The ▁econom ics ▁seemed ▁simple ▁enough ; ▁since ▁ro cket ▁costs ▁increase ▁rapidly ▁with ▁size , ▁the ▁price ▁of ▁the ▁IC B M ▁launch ing ▁a ▁large ▁war head ▁should ▁always ▁be ▁greater ▁than ▁the ▁much ▁smaller ▁inter ceptor ▁miss ile ▁needed ▁to ▁destroy ▁it . ▁In ▁an ▁arms ▁race ▁the ▁defense ▁would