And so, in conclusion, from the aforementioned,
it can be ascertained that the Light Brigade - which
the reader will discern was the moniker applied to a cavalry
unit of courageous soldiers - was attacked on both sides
by their adversarial enemy as they rode their horses
in a downhill fashion into a valley. The poet calls it the
“Valley of Death” but that is highly unlikely to be the
actual name of the valley. We can infer from the
utilization of the valley’s title in this manner that the
poet was in actual fact using the phrase metaphorically
in order to indicate to the reader that members of the
cavalry unit were being shot and killed by the
enemy in that particular location. This is in contrast to
Twain’s metaphorical river that Huck and Jim go
down but are not shot at.

Professor Poetry Hound

http://www.poemhunter.com/poem/alternative-voicing-charge-of-the-lightweight-brigade/