Complex sentence: Firstly, a squad of soldiers firing volleys would be completely unable to see their targets after a few shots; and secondly, their location would be obvious because of the huge cloud of white smoke hanging over them.
Split into simpler sentences: Firstly, a squad of soldiers firing volleys would be completely unable to see their targets after a few shots. Secondly, their location would quickly be obvious because of the huge cloud of white smoke hanging over them.