What is heroic about the actions of the lieutenant in chapter 20?

The lieutenant, leaning on his sword like a cane, looks as if he feels all is lost. The smoke curls lazily as men hide from bullets. Suddenly, the lieutenant sees that the Rebels are attempting to sneak up on the regiment. The troops fire a quick volley at the approaching foes. Their uniforms were gray and looked new. They were not expecting the resistance that met them. The two groups of soldiers exchange volleys like boxers exchange blows. By ducking and dodging, Henry has glimpses of these men through the smoke.