In "Anthem for Doomed Youth," war is not what we might expect. Owen is all about exploring how war can twist the way we see the world; men become cattle, artillery shells become choirs, and tears become candles. Things in a world at war are not as they seem. In our speaker's eyes, the rituals of mourning the fallen become mockeries, because they ring so hollow in the face of war's true horrors.
Line 1: Using a simile to compare the battlefield deaths of soldiers to the slaughter of cattle conveys both the inhumanity of these soldiers' deaths, and also that they just might be dying without really understanding why. They're headed off to slaughter, no questions asked.
Line 2: Attributing anger, a very human emotion, to the guns, which are mere machines – is the first instance of personification in a poem that uses an awful lot of personification. It's interesting to note that while the soldiers are being dehumanized, the instruments of war are actually, in a strange and terrifying way, becoming more human. Yowza.
Line 3: The anaphora at the beginning of this sentence (starting with "Only the," just like the line before) helps build momentum, since when we hit the phrase a second time we pay a little more attention. If something's repeated it's supposed to be important, right? Plus, that momentum and the repetition of "only" add to the tension and horror of the battlefield, where there's nothing but shells and dying men.
Line 3: The alliteration at the end of the line—"rifles' rapid rattle"—is another way of grabbing our attention and building the intensity. Ramping up the momentum and intensity is obviously very important here, since our speaker's throwing us into the middle of a war zone, and must get the sheer terror across to us through the language.
Lines 3-4: Adding on to that alliteration is some more consonance. Just check out all those double "t" words—"stuttering," "rattle," and "patter." And, hey, why not throw in that "p" sound in "rapid" while you're at it? Beyond being fun to say aloud, all this consonance also mimics the sound of the rifles firing. After all there's a lot of "r" and " t" sounds, and what's the way we usually represent gunfire? Yup: "ratatat tat" (or something like that). So all those sounds give us a sensory experience of the battlefield. Not only are we reading about it; we feel like we're there.
Line 7: The implied metaphor here (the shells are demented choirs) continues the trend of personifying the weapons of war, but we should also notice that it goes the other way as well by turning humans and human institutions (choir members and churches) into inanimate weapons. The metaphor, by comparing them, blurs the lines between a choir singing for the glory of God and country, and the shelling that just might be a result of, or at the very least related to, that same nationalistic and patriotic fervor.