Two of the most moving songs about war are to be found on Richard Thompson's album Daring Adventures: How Will I Ever Be Simple Again? and Al Bowlly's In Heaven. They're not overtly anti-war, which makes them that much more powerful, I think. And in fact one of his very greatest songs, Woods of Darney, is also about war, specifically the First World War.
All of those songs are written from the point of view of soldiers or ex-soldiers, and tell of the suffering and sacrifices humble soldiers have to go through. As he included Phil Ochs's I Ain't Marching Anymore in his recent gig, I think it's clear where he stands. And another great war song, more obviously anti, which I don't think has been mentioned yet, is Bob Dylan's With God On Our Side. Perhaps the definitive version of it is by the Neville Brothers, on their Yellow Moon album. It's a spine-tingling rendition by Aaron, and still packs a mighty punch today - I'm listening to it right now. Azeem in London