Lost in the swamp and welter of the pit,
He flounders off the duck-boards; only he knows
Each flash and spouting crash,--each instant lit
When gloom reveals the streaming rain. He goes
Heavily, blindly on. And, while he blunders,
"Could anything be worse than this?"--he wonders,
Remembering how he saw those Germans run,
Screaming for mercy among the stumps of trees:
Green-faced, they dodged and darted: there was one
Livid with terror, clutching at his knees. . .
Our chaps were sticking 'em like pigs . . . "O hell!"
He thought--"there's things in war one dare not tell
Poor father sitting safe at home, who reads
Of dying heroes and their deathless deeds."

Siegfried Sassoon

http://www.poemhunter.com/poem/remorse-2/