The "red badge of courage" to which author Stephen Crane refers in the title of his classic Civil War novel is simply a battle wound that a soldier receives during combat. It is something that young Henry both fears and desires. Henry worries most about whether he will "skedaddle"--run away--when the action gets too hot, and sure enough, he does just that after his regiment absorbs a second Confederate attack. But when Henry encounters a group of wounded men heading to the rear, he prefers to be in their place.
At times he regarded the wounded soldiers in an envious way. He conceived persons with torn bodies to be peculiarly happy. He wished that he, too, had a wound, a red badge of courage. (Chapter IX)
Henry eventually gets his wish. He, too, receives "a little red badge," but it comes in a most ironic manner: He is assaulted by a fellow Union soldier after the massive Confederate attack has driven the Union troops in disorder. When Henry tries to gain information from the soldier, he is clubbed with the man's weapon.
The red badge—a soldier's wound—is the most obvious symbol in the book and the source of its greatest irony. While it is meant to be a sign of honor and courage, gamed from true action in war, Henry's red badge was given to him by accident by one of his own army and clearly not from brave battle. Henry lies about this and creates a pretense to his men that is accepted.
Henry's "red badge" allows him to cover up his cowardly "skedaddle," and it creates a change, both in him internally and in the perception that his comrades have of him.