▁series , ▁AS SET ▁and ▁P RI ME . ▁ ▁This ▁research ▁was ▁eventually ▁put ▁to ▁use ▁in ▁the ▁Pers hing ▁II ' s ▁MAR V ▁re entry ▁vehicle . ▁In ▁this ▁case , ▁there ▁is ▁no ▁extended ▁gl iding ▁phase ; ▁the ▁war head ▁uses ▁lift ▁only ▁for ▁short ▁periods ▁to ▁adjust ▁its ▁traject ory . ▁This ▁is ▁used ▁late ▁in ▁the ▁re entry ▁process , ▁combining ▁data ▁from ▁a ▁S inger ▁K ear f ott ▁in ert ial ▁navigation ▁system ▁with ▁a ▁Go ody ear ▁A eros pace ▁active ▁rad ar . ▁Similar ▁concepts ▁have ▁been ▁developed ▁for ▁most ▁nuclear - ar med ▁nations ' ▁theatre ▁ball istic ▁miss iles . ▁ ▁In ▁contrast ▁to ▁these ▁man eu ver ing ▁war head ▁concepts , ▁there ▁has ▁been ▁growing ▁interest ▁in ▁the ▁traditional ▁boost - g lide ▁concept ▁not ▁to ▁extend ▁range ▁per ▁se , ▁but ▁to ▁allow ▁it ▁to ▁reach ▁a ▁given ▁range ▁while ▁flying ▁at ▁a ▁much ▁lower ▁alt itude . ▁The ▁goal , ▁in ▁this ▁case , ▁is ▁to ▁keep ▁the ▁re entry ▁vehicle ▁below ▁rad ar ▁coverage ▁until ▁it ▁enters ▁the ▁terminal ▁phase . ▁Such ▁a ▁system ▁is ▁assumed ▁to ▁be ▁used ▁on ▁the ▁Chinese ▁D F - 2 1 D ▁anti - ship ▁ball istic ▁miss ile , ▁which ▁is ▁also ▁believed ▁to ▁man eu ver ▁during ▁the ▁terminal ▁phase ▁to ▁make ▁inter ception ▁more ▁difficult . ▁The ▁later ▁D F - 2 6 , ▁a ▁development ▁of ▁the ▁D P - 2 1 , ▁may ▁be