The change in Himmelstoss' character also serves to illustrate the difference between the empty talk of those not actually fighting in the trenches, and the nightmarish reality for those who do. Himmelstoss is all bark and no bite; but then again, very few have a bite left for very long once they are exposed to the insane conditions of the front lines.
Himmelstoss serves as a tyrant-like figure who seeks personal pleasure from seeing those placed into his basic training platoon suffer greatly. He claims that everything they are doing is due to the war effort--a preparatory push for all of the things they are likely to see and experience while at the front line.
However, he does something inappropriate later in the novel (around chapter 5) in which his commanding officers dismiss him from his drill sergeant position and send him to the front lines, a place where it appears he's never actually experienced after all.
It is there that Tjaden and the others stand up to Himmelstoss, regardless of his superiority in rank. The first time in which the reader sees Himmelstoss on the front line is when he is shown huddling in a corner of a trench with his face in his hands (obviously crying).
The juxtaposition of Himmelstoss' character before war and while in war goes to show the reader of the fragility of character and personal ideals while dealing with this new type of chemical and mechanical war--it is nothing like anyone's ever experienced before. Specifically, it is nothing like Himmelstoss has ever experienced before.