When you have one or more battalions selected and press both mouse buttons you are able to organize your units into battle formations. In this each kind of unit is assigned a sword symbol, spearhead symbol, star symbol (for heroes and usually special one-person units, like Lothlórien's minstrels), or a bow symbol. Those determine the position from rear to front each kind of unit will occupy, with spearhead units coming on front, followed by "sword" units etc.
Currently Galahadrin are "bow" units, could you make them into sword units?
Thank you.