Morality and War

I've always been intrigued by the notion that in warfare, in our modern times, we expect behavior of the highest moral standards from our soldiers.
In this sense, I think soldiers are sent into battle with one arm tied behind their back. For example, for any soldiers posted in Afghanistan, who is and who isn't a soldier/insurgent/freedom fighter isn't clear. If they make a mistake and kill a civilian, they are put on trial.
What I find paradoxical is that when it comes to indiscriminate mass bombings of civilians there never has and probably never will be moral outrage. Hiroshima and Nagasaki were "necessary" and nobody seems to talk about the bombing of Dresden during WWII.
Yet, the Mai Lai massacre is etched in the minds of those who lived at the time and can recall the outrage against the soldiers involved. The Vietnam war will no doubt be a case study of moral dilemmas faced by soldiers in battle for years to come.
So, for the modern soldier, knowing what is and  isn't acceptable during warfare becomes a walk on the moral tightrope. I'm no moralist or philosopher who can make proclamations on this subject.
 I just feel a quiet outrage for Canadian soldier who has been put on trial for what is described as a "mercy killing". Robert Semrau has been treated appallingly by his superiors.He still faces a possible five years jail sentence.
I wonder if soldiers have classes in ethics along with weapons training and unarmed combat training. If we want them to uphold the highest moral standards then maybe we should consider classes in the philosophy of ethics.
I hope nobody takes this suggestion seriously.