Complex sentence: It shows the Highlanders still wearing the plaids which they normally set aside before battle, where they would fire a volley then run full tilt at the enemy with broadsword and targe, wearing only their shirts.
Split into simpler sentences: It shows the Highlanders still wearing the plaids which they normally set aside before battle. They would fire a volley then run full tilt at the enemy with their weapons, wearing only their shirts.