. ▁ ▁This ▁allows ▁the ▁shoot er ▁to ▁vis ually ▁trace ▁the ▁flight ▁path ▁of ▁the ▁project ile ▁and ▁thus ▁make ▁necessary ▁ball istic ▁corre ctions , ▁without ▁having ▁to ▁confirm ▁project ile ▁impact s ▁and ▁without ▁even ▁using ▁the ▁s ights ▁of ▁the ▁weapon . ▁ ▁T rac er ▁fire ▁can ▁also ▁be ▁used ▁as ▁a ▁mark ing ▁tool ▁to ▁signal ▁other ▁shoot ers ▁to ▁concent rate ▁their ▁fire ▁on ▁a ▁particular ▁target ▁during ▁battle . ▁ ▁When ▁used , ▁trac ers ▁are ▁usually ▁loaded ▁as ▁every ▁fifth ▁round ▁in ▁machine ▁gun ▁bel ts , ▁referred ▁to ▁as ▁four - to - one ▁trac er . ▁Pl ato on ▁and ▁squad ▁leaders ▁will ▁load ▁some ▁trac er ▁r ounds ▁in ▁their ▁magazine ▁or ▁even ▁use ▁sole ly ▁trac ers ▁to ▁mark ▁targets ▁for ▁their ▁soldiers ▁to ▁fire ▁on . ▁ ▁T rac ers ▁are ▁also ▁sometimes ▁placed ▁two ▁or ▁three ▁r ounds ▁from ▁the ▁bottom ▁of ▁mag az ines ▁to ▁alert ▁shoot ers ▁that ▁their ▁weapons ▁are ▁almost ▁empty . ▁During ▁World ▁War ▁II , ▁aircraft ▁with ▁fixed ▁machine ▁guns ▁or ▁can n ons ▁mounted ▁would ▁sometimes ▁have ▁a ▁series ▁of ▁trac er ▁r ounds ▁added ▁near ▁the ▁end ▁of ▁the ▁am mun ition ▁bel ts , ▁to ▁alert ▁the ▁pilot ▁that ▁he ▁was ▁almost ▁out ▁of ▁am mun ition . ▁However , ▁this ▁practice ▁similarly ▁alert ed ▁ast ute ▁enemies ▁that ▁their ▁fo es ▁were ▁nearly ▁out ▁of ▁am mun ition . ▁More ▁often , ▁however , ▁the ▁entire ▁magazine ▁was