[wade-w]

Yes there are huge grey areas here, especially during combat. At times like those, stopping to question whether or not an order is legal is likely to get people killed. But when you are a guard in a POW camp and sarge tells you to torture a prisoner, that is clearly an unlawful order. If you are caught you will be held accountable for following it. In fact, this is exactly the type of situation that this policy was designed for.

The only guard duty I ever pulled had rather stringent and specific orders on the use of deadly force. If anyone came past my post without my express permission, I was required to shoot to kill immediately and without further warning. There were no exceptions to this order; it explicitly included friendly personnel, even shipmates. However, under the circumstances, I considered these to be lawful orders.

As for holding the entire military culpable because an invasion violates international law, I'd say no. The decision to go to war is a political one, and not something that the military should have any control over. Once your government decides to fight, it doesn't matter whether or not that government has international approval; the military is obligated to comply.