No one keeps a straight line in battle these days. In fact in more advanced combat training excessive regularity in your squad's movement gets drilled out of you. Modern combat has relied on variations of skirmish rules, which have been around at least since the US Revolution. Things like staggering out your squad so one shot can't take down more than 2 people... which just became several times more important with repeating arms.

Getting in a straight line in a combat zone? Don't make me laugh.