>"Battlefield" has become a somewhat murky concept - especially in asymetric warfare. If I am a soldier in Iraq and I catch a guy planting an IED are we on a battlefield? Is he a "criminal" Does he have rights under US law?

If the US law somehow applies to a citizen of a foreign country, then that country is de facto a colony. The US then have all the obligations as an occupying force, as per Geneva convention - they need to provide a lot. Which they have failed for five years, and keep failing. So why not give up if not up to the task?