themes
warfare
"The Charge of the Light Brigade" is a poem about a battle. It spends a lot of time describing the confusion, the terror, the bloodshed, and, yes, also the heroism and excitement of armed combat.
courage
Every last one of them charges forward to the enemy line and does his job. Tennyson makes sure to point out that they know exactly how dangerous and hopeless the job is, but they stand up and do it anyway. "The Charge of the Light Brigade" is about the heroism of ordinary, nameless soldiers.
duty
The Brigade doesn't need to go on a suicide mission and charge their enemies (some commander seems to have given a bad order), and the Brigade knows that, but they do it anyway. That's the code of a soldier,
death
The tragedy here is that many of the brave soldiers in the Light Brigade die in this battle. Death is everywhere in this poem.