Seeing through the "misty panes and thick green light" of a world suddenly turned upside-down by the dropping of gas shells, we're dragged through horrors that seem too terrible to be real, and too real to be anything but first-hand experience (13). It's a world peopled by the walking dead. Soldiers tramp through mud and gore, their own bodies falling apart as they move slowly towards their tents. Even the flares overhead (thrown to alert bombers about potential targets) are "haunting," suggesting that the battlefield itself may be one step closer to the afterlife than even the soldiers would like to think. Owen describes the scene as incredibly gruesome, and he's more than willing to walk us through it in excruciating detail.
By the end of the poem, we seem to have moved off the actual battlefield, or have we? The poem turns inward, becoming a mindscape of the speaker's nightmares. Because we've already gotten a good sense of just how nightmarish actual battle scenes are, however, the difference between the speaker's mind and a minefield doesn't seem to be that great.
It's a clever move on Owen's part: there's no difference between the awful scenes of wartime and the traumatized mind of a soldier after battle because the soldier's mind never leaves the battlefield. See how crafty that is? When our speaker cries out, "In all my dreams, before my helpless sight, He plunges at me, guttering, choking, drowning," we can't tell whether he's still in the war or looking back on his experiences months (or years) afterwards. There are some settings that you just can't get out of your system.