“Men marched asleep.”
Given that this is a war poem you’d think the author would specify the men as Soldiers but instead he names them men. I believe the author does so to create an image of broken soldiers who at their roots are only men. I picture these men questioning how far they will march on to protect their country. They have already been through hell so how much more can they handle.
“As under a green sea, I saw him drowning.”
In the chaos of war mustard gas was released, spreading everywhere on the battleground. From the authors point of view he sees a single man suffocating in the gas. “I saw him drowning” is a short yet extremely vivid sentence for me because it really shows how cruel
Simile: like a devil’s sick of sin;
Metaphor: As under a green sea, I saw him drowning.
Repetition: Gas! GAS!