Owen describes the soldiers as:
"Bent double like old beggars under sacks,
Knock need, coughing like hags, we cursed through sludge"
The use of similes immediately undermines the traditional heroic nature of war and the soldiers, it compares the soldiers to unheroic things, old woman and sick beggars who are finding it difficult to breathe.
This creates an inglorious atmosphere, these men aren't strong but 'bent' nearly in half stooping forward with exhaustion.
The unusual word choice of the verb 'cursed' has a double meaning: the soldiers are swearing as they walk, but also feel they are 'cursed' by their involvement in the war.