Murder is the deliberate and unjustified killing of an another human being. A combatant taking the life of an enemy combatant in the lawful exercise of his sworn duty is acting justifiably, therefore it's not murder. I'm not saying war itself is a morally good thing and that the lives lost aren't tragic.
Sorry, I am having none of it. War is no justification for murder, and no word-juggling will change that.