We think "The Charge of the Light Brigade" is a textbook example of a poem that uses its language to recreate the sounds it's describing. In this case, that sound would be the noises of battle.
The dactylic meter of the poem reminds us of the booming of cannon, the way there's a heavy explosion at first that dies away slowly. (Not sure what dactylic meter is? Check out "Form and Meter.") Read this line out loud: "Cannon to right of them" (39). Hear how the word CANNON explodes on your ear? Then everything else in the line gets less emphasis, dying away as if it was echoing back and forth off the walls of the "valley of Death." BOOM-boom-boom.
We also hear the clattering of hoof beats everywhere in these lines: "Boldly they rode, and well" (line 23). That first word doesn't pound on your ear like the "Cannon" in line 39. Instead, we hear, a steady, "Rat tat a tat," like horses running desperately across the hard baked earth of the valley. All these noises make a sort of concert and, in our opinion, help to pull you completely into the world of the poem.