The shitfield is the perfect metaphor for war. It connects so well, and is so obvious, that it is difficult for most of us to translate it into words. I suppose the most blatantly obvious connection is between the shit itself and the fact that war sucks. Nobody associates fecal matter with anything good, and the phrase “that's crap” is used to convey a feeling of disappointment or anger.
	However, we must inspect the subtleties of this analogy. I believe that one part of this metaphor that often goes undetected is stickiness of the mud and poo in the field. They make it hard to move, hard to escape, which is the same feeling that the atmosphere of any war conveys to its participants-- they can't escape, and it is nearly impossible to make progress  in any direction (including mentally and emotionally).
	I would also like to visit the point regarding the smell of the shitfield. I believe this ties in directly to the all-pervasiveness of war. Even when soldiers aren't actively fighting or on patrol, or even when they're in a relatively peaceful part of the world, there is still some idea or feeling of the war that they feel. And, not to overstate the obvious, the shitfield stinks, as does war. Yet another obvious analogy.
	And then there is the shitfield's ability to make finding things impossible. The most glaring example is Kiowa's body: when he died, it took hours to find his corpse, and even longer to dig it up. This directly reflects how war in general treats the dead: it buries them, makes them unimportant. However, instead of taking hours to remember  and let go (find and bury) of the dead, it takes veterans years, even decades, before they can fully lay the spirits of their comrades to rest.
	The last idea I would like to visit is that of concentration. Just as the shitfield is a place for people to concentrate their excrement and thus save the rest of their environment by destroying a small portion of it, war is a thing that allows people to take out years of accumulated rage and hate and concentrate it into one relatively small place and time (admittedly, the Vietnam war lasted for a long time, but most wars didn't take nearly as long). We use war to take our need to fight somewhere else, anywhere besides our own homes, and thus maintain domestic tranquility while destroying someone else's homeland.