How does Henry react during his first battle in Red Badge of Courage, and what is the outcome of the battle?

Henry had long feared how he would behave under battle conditions.   He had wanted to act bravely and heroically, but was afraid that when the time came, he might shame himself by running away.  As it turns out, Henry discovers that he has very little influence over his own actions when he is finally tested on the field of battle.  When the enemy threatens, his actions become automatic; it is as if he becomes a part of a machine.

Immediately before the violent encounter with the opposing army, Henry is started by the thought that his weapon might not be loaded.  He tries "to rally his faltering intellect...but he (can)not".  At the instant of engagement, he finds himself reacting mechanically,

"...before he (has) announced to himself that he (is) about to fight - he (throws) the obedient, well-balanced rifle into position and fire(s) a first wild shot.  Directly he (is) working at his weapon like an automatic affair...he suddenly (loses) concern for himself, and for(gets) to look at a menacing fate.  He be(comes) not a man but a member".

Henry is

"welded into a common personality", a part of a "subtle battle brotherhood more potent even than the cause for which they (are) fighting.  It (is) a mysterious fragernity born of the smoke and danger of death".

Under battle conditions, Henry finds that choice is not really a factor.  He acts without thinking, ruled by instinct, following the actions of everyone else like a dumb beast (Chapter 4-5).

The outcome of the battle is positive for Henry's side.  The enemy charge is repulsed; in the midst of all the chaos, somehow Henry's army has managed to hold the opposing forces back (Chapter 5).