The tragedy here is that many of the brave soldiers in the Light Brigade die in this battle. Tennyson doesn't say how many, and he doesn't go into gory details. Still, death is everywhere in this poem. It's a constant presence, almost like a character. The valley where the charge takes place belongs to "Death"; we hear all about his jaws, and so forth. Death is almost a physical presence in "The Charge of the Light Brigade," something you could see and touch, like the Grim Reaper.
This poem shelters its readers from the actual violence of war by dealing with death almost entirely as a symbol or an idea, rather than a bloody fact.
By helping to preserve the memory of these men, "The Charge of the Light Brigade" gives their deaths real and lasting meaning.