▁be ▁many ▁times ▁more ▁expensive ▁than ▁the ▁IC B M s ▁they ▁def ended ▁against . ▁ ▁The ▁Anti - B all istic ▁Miss ile ▁Tre aty ▁of ▁ 1 9 7 2 ▁ ▁Techn ical , ▁economic ▁and ▁political ▁problems ▁described ▁resulted ▁in ▁the ▁AB M ▁treat y ▁of ▁ 1 9 7 2 , ▁which ▁restricted ▁the ▁deployment ▁of ▁strateg ic ▁( not ▁tact ical ) ▁anti - ball istic ▁miss iles . ▁ ▁By ▁the ▁AB M ▁treat y ▁and ▁a ▁ 1 9 7 4 ▁revision , ▁each ▁country ▁was ▁allowed ▁to ▁deploy ▁a ▁mere ▁ 1 0 0 ▁AB M s ▁to ▁protect ▁a ▁single , ▁small ▁area . ▁The ▁S ovi ets ▁retained ▁their ▁Moscow ▁def ences . ▁The ▁U . S . ▁designated ▁their ▁IC B M ▁sites ▁near ▁Grand ▁F ork s ▁Air ▁Force ▁Base , ▁North ▁Dak ota , ▁where ▁Saf egu ard ▁was ▁already ▁under ▁advanced ▁development . ▁The ▁rad ar ▁systems ▁and ▁anti - ball istic ▁miss iles ▁were ▁approximately ▁ 9 0 ▁miles ▁north / n orth west ▁of ▁Grand ▁F ork s ▁A FB , ▁near ▁Con crete , ▁North ▁Dak ota . ▁The ▁miss iles ▁were ▁de activ ated ▁in ▁ 1 9 7 5 . ▁The ▁main ▁rad ar ▁site ▁( PAR CS ) ▁is ▁still ▁used ▁as ▁an ▁early ▁warning ▁IC B M ▁rad ar , ▁facing ▁relative ▁north . ▁It ▁is ▁located ▁at ▁Caval ier ▁Air ▁Force ▁Station , ▁North ▁Dak ota . ▁ ▁Br ief