'While horse and hero fell / They that had fought so well / Came thro' the jaws of Death' - What metaphor has Alfred Lord Tennyson used in these lines from his poem, 'The Charge of the Light Brigade'?

A metaphor states that one thing is something else. This description, however, is too simple for the way metaphors often work in poetry, literature and speeches. You will often find something being described, or written about, as if it is something else, without the writer ever saying 'x is y' (do you see the mathematical metaphor there?).