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The atmosphere of war would be what it alludes to: the violence and chaos of the battlefield. Henry is not fighting the enemy men so much as the swirling battle phantoms that surround him. He hears men speak around him as if he were sleeping. While he fights more against "swirling battle phantoms" than other men, Henry is creating the smoke of battle and the smoke of uncertainty himself, along with the other troops. They fire into a din of battle as if in a sleep. This can certainly happen in warfare today. Both fear and exhaustion can lure a soldier into a trance-like state as they shoot into a void.