Why does Tommo give up all hope of Charlie returning to the dugout alive?

The Germans feel invincible. Into the German trenches the Allies surge, read to finish the war. The enemy is nowhere to be seen, but the Allies continue forward. The Germans begin another bombardment, this time of their own trenches, to dive the Allies out. After falling back to their trench, Thomas notices that Charlie is not back. All night and the next day, Thomas hopes that his brother will arrive. Just when Thomas thinks that Charlie must certainly be dead, he hears Charlie announcing himself at the edge of the trench. Thomas is on sentry duty when Charlie arrives back, shot through the foot. Charlie gets to go home for surgery, but he will be back. When Thomas's company returns at Pop for more training, they find that their new commander is none other than Horrible Hanley himself.