▁presented ▁by ▁surrounding ▁hills ▁or ▁mountains ▁to ▁keep ▁war head s ▁away ▁from ▁the ▁sil os ▁in ▁the ▁valle ys ▁between ▁them . ▁War head s ▁approach ▁on ▁a ▁shall ow ▁traject ory , ▁so ▁mountains ▁or ▁mes as ▁with ▁ste ep ▁sides ▁would ▁mean ▁the ▁war head ▁would ▁impact ▁the ▁terrain ▁before ▁reaching ▁the ▁sil o . ▁ ▁TR W ▁suggested ▁building ▁three ▁bases ▁with ▁thirty ▁miss iles ▁each , ▁and ▁estimated ▁that ▁one ▁of ▁the ▁three ▁bases ▁would ▁surv ive ▁an ▁all - out ▁counter force ▁attack . ▁To ▁ensure ▁that ▁ 6 0 0 ▁war head s ▁would ▁surv ive , ▁each ▁miss ile ▁would ▁have ▁to ▁carry ▁about ▁ 2 0 ▁war head s . ▁These ▁studies ▁led ▁to ▁the ▁Miss ile , ▁Ex perimental , ▁or ▁M X , ▁project , ▁which ▁started ▁in ▁ 1 9 7 1 . ▁The ▁design ▁rapidly ▁fir med ▁up , ▁emer ging ▁with ▁ten - war head s ▁on ▁more ▁miss iles ▁in ▁order ▁to ▁raise ▁the ▁surv iv ors ▁to ▁ 1 , 0 0 0 ▁war head s . ▁But ▁the ▁bas ing ▁became ▁not ▁so ▁much ▁a ▁specific ▁concept ▁as ▁a ▁catch - all ▁program ▁for ▁every ▁possible ▁concept , ▁from ▁railway ▁deploy ments , ▁to ▁under ground ▁rac etra cks , ▁to ▁mobile ▁systems . ▁A ▁review ▁of ▁the ▁options ▁written ▁in ▁the ▁mid - 1 9 7 0 s ▁ran ▁into ▁hundreds ▁of ▁pages . ▁ ▁Hard point ▁and ▁Hard site ▁ ▁Through ▁the ▁ 1