▁ ▁C ounter me asures ▁While ▁flying ▁below ▁the ▁oper ational ▁en velope ▁of ▁Ex o at mos pher ic ▁Kill ▁Ve h icles , ▁the ▁trade off ▁with ▁H GV s ▁in ▁comparison ▁to ▁conventional ▁M IR V s ▁are ▁many - fold , ▁including ▁no ▁need le ▁in ▁a ▁hay stack ▁protection ▁from ▁miss ile ▁de co ys ▁and ▁both ▁less ▁speed ▁and ▁alt itude ▁as ▁they ▁near ▁the ▁target , ▁meaning ▁that ▁H GV s ▁are ▁more ▁easily ▁intercept ed ▁by ▁low - t ier ▁intercept ors , ▁some ▁examples ▁of ▁which ▁include ▁the ▁high ▁thrust ▁Mach ▁ 1 0 ▁S print ▁miss ile ▁which ▁was ▁in ▁service ▁briefly ▁from ▁ 1 9 7 5 ▁to ▁ 1 9 7 6 , ▁its ▁US ▁derivatives , ▁and ▁the ▁still ▁oper ational ▁Mach ▁ 1 7 ▁Russian ▁ 5 3 T 6 , ▁AB M - 3 ▁Gaz elle . ▁Moreover , ▁the ▁possible ▁re - emer gence ▁of ▁nuclear ▁or ▁hit - to - kill ▁str atos phere ▁reaching ▁guns , ▁gu ided ▁and ▁triggered ▁by ▁forward ▁operating ▁flight - path ▁sens ors ▁- ▁for ▁example , ▁the ▁ 2 0 1 6 ▁Hyper vel ocity ▁Project ile ▁( H VP ) ▁in ▁development ▁for ▁the ▁M 1 0 9 ▁how itzer ▁- ▁could ▁also ▁decrease ▁H GV ▁surv iv ability . ▁ ▁Other ▁more ▁spec ulative ▁counter - h yp erson ic ▁vehicle ▁measures ▁may ▁involve ▁las er ▁or ▁rail ▁gun ▁techn ologies . ▁ ▁However , ▁Russian ▁sources