▁The ▁loss ▁of ▁mass ▁en ▁route ▁to ▁the ▁target ▁sever ely ▁affected ▁the ▁bullet ' s ▁ball istics . ▁ ▁The ▁United ▁Kingdom ▁was ▁the ▁first ▁to ▁develop ▁and ▁introduce ▁a ▁trac er ▁round , ▁a ▁version ▁of ▁the ▁. 3 0 3 ▁cart ridge ▁in ▁ 1 9 1 5 . ▁The ▁United ▁States ▁introduced ▁a ▁. 3 0 - 0 6 ▁trac er ▁in ▁ 1 9 1 7 . ▁ ▁Prior ▁to ▁adopt ing ▁red ▁( and ▁later , ▁other ▁color ) ▁bullet ▁tips ▁for ▁trac ers , ▁American ▁trac ers ▁were ▁identified ▁by ▁black ened ▁cart ridge ▁cases . ▁ ▁T rac ers ▁proved ▁useful ▁as ▁a ▁counter measure ▁against ▁Ze ppel ins ▁used ▁by ▁Germany ▁during ▁World ▁War ▁I . ▁The ▁air ships ▁were ▁used ▁for ▁reconna issance , ▁surve ill ance ▁and ▁bomb ing ▁operations . ▁Normal ▁bul lets ▁merely ▁had ▁the ▁effect ▁of ▁causing ▁a ▁slow ▁leak , ▁but ▁trac ers ▁could ▁ign ite ▁the ▁hydro gen ▁gas b ags , ▁and ▁bring ▁down ▁the ▁air ship ▁quickly . ▁ ▁In ▁World ▁War ▁II ▁US ▁naval ▁and ▁marine ▁air cre w ▁were ▁issued ▁trac er ▁r ounds ▁with ▁their ▁side ▁arms ▁for ▁emer gency ▁signal ing ▁use ▁as ▁well ▁as ▁defense . ▁ ▁Const ruction ▁▁ ▁A ▁trac er ▁project ile ▁is ▁constructed ▁with ▁a ▁h ollow ▁base ▁filled ▁with ▁a ▁py rote chn ic ▁f lare ▁material , ▁made ▁of ▁a ▁mixture ▁of ▁a ▁very ▁fin ely ▁ground ▁met all ic ▁fuel , ▁ox id