▁War , ▁the ▁Army ▁of ▁the ▁United ▁States ▁consisted ▁of ▁cons cript s ▁in ▁the ▁Reg ular ▁Army , ▁with ▁the ▁National ▁Guard ▁and ▁Army ▁of ▁the ▁United ▁States ▁existing ▁simultaneously ▁in ▁the ▁same ▁the ater . ▁The ▁system ▁of ▁prefix es ▁before ▁service ▁numbers ▁was ▁as ▁follows : ▁ ▁ER : ▁▁▁▁▁▁▁▁ ▁En list ed ▁Reserve ▁OR : ▁▁▁▁▁▁▁▁ ▁Officer ▁Reserve ▁N G : ▁▁▁▁▁▁▁▁ ▁National ▁Guard ▁RA : ▁▁▁▁▁▁▁▁ ▁Reg ular ▁Army ▁US : ▁▁▁▁▁▁▁▁ ▁Army ▁of ▁the ▁United ▁States ▁ ▁. ▁ ▁The ▁last ▁use ▁of ▁the ▁Army ▁of ▁the ▁United ▁States ▁( A US ) ▁was ▁during ▁the ▁Vietnam ▁War . ▁It ▁was ▁dis band ed ▁in ▁ 1 9 7 4 . ▁ ▁Administr ative ▁usage ▁ ▁The ▁Army ▁Reserve ▁( US AR ) ▁and ▁Army ▁National ▁Guard ▁( AR NG ) ▁remained ▁separate ▁components ▁during ▁the ▁modern ▁era ▁of ▁cons cription , ▁and ▁their ▁members ▁continued ▁to ▁use ▁their ▁unique ▁ident ifiers , ▁except ▁in ▁those ▁cases ▁in ▁which ▁officers ▁were ▁appointed ▁or ▁commission ed ▁into ▁a ▁higher ▁grade ▁of ▁rank ▁while ▁on ▁active ▁duty ▁serving ▁in ▁a ▁Reg ular ▁Army ▁unit . ▁For ▁example , ▁during ▁the ▁war ▁in ▁Vietnam , ▁a ▁gradu ate ▁of ▁Army ▁R OT C , ▁commission ed ▁as ▁a ▁US AR ▁ 2 d ▁lieutenant ▁and ▁serving ▁his ▁initial ▁active ▁duty ▁tour , ▁could ▁be ▁promoted ▁to ▁ 1 st ▁lieutenant , ▁or ▁even ▁captain , ▁with ▁a ▁" tem por ary ", ▁active ▁duty ▁( i . e ., ▁A