▁Do ctrine , ▁which ▁called ▁for ▁the ▁US ▁to ▁exit ▁Vietnam ▁and ▁leave ▁the ▁combat ▁to ▁P AV N , ▁a ▁process ▁later ▁known ▁as ▁Vietnam ization . ▁It ▁also ▁re - f oc used ▁the ▁military ▁on ▁combat ▁against ▁Soviet - led ▁forces ▁in ▁Europe . ▁Through ▁this ▁period ▁the ▁USS R ▁had ▁reached ▁a ▁level ▁of ▁par ity ▁in ▁strateg ic ▁nuclear ▁weapons , ▁and ▁US ▁leaders ▁concluded ▁that ▁employ ing ▁nuclear ▁weapons ▁in ▁any ▁form ▁might ▁lead ▁to ▁mut ual ▁anni h ilation . ▁Given ▁the ▁W TO ' s ▁ 3 - to - 1 ▁superior ity , ▁NAT O ▁would ▁lose ▁a ▁ground ▁war ▁with ▁or ▁without ▁the ▁use ▁of ▁tact ical ▁nuclear ▁weapons , ▁and ▁that ▁only ▁the ▁" mac ab re ▁option " ▁of ▁a ▁strateg ic ▁exchange ▁might ▁save ▁it . ▁Given ▁increasing ▁fis cal ▁rest raint , ▁the ▁Army ▁simply ▁could ▁not ▁purchase ▁enough ▁t anks ▁to ▁offset ▁this ▁im bal ance , ▁and ▁the ▁attack ▁hel ic opter ▁appeared ▁to ▁be ▁an ▁alternative ▁that ▁was ▁" a ▁relatively ▁cheap , ▁flexible ▁and ▁highly ▁pot ent ▁weapons ▁system ." ▁ ▁Tri al ▁by ▁fire ▁The ▁A AF SS ▁contest ▁resulted ▁in ▁a ▁complex ▁design ▁who ' s ▁development ▁drag ged ▁on ▁for ▁years ▁before ▁it ▁was ▁eventually ▁can ce led . ▁Looking ▁for ▁inter im ▁design ▁to ▁quickly ▁deploy ▁to ▁V iet ▁Nam , ▁the ▁A H - 1 ▁Cob ra ▁was ▁introduced ▁in ▁combat ▁in ▁ 1 9 6 8 . ▁ ▁Between