The speaker imagines escaping a war as a bird, slipping through a pigeon hole and rising above the battlefield. Up in the clouds, the noise of gunfire fades and they can finally think and feel like themselves, free from the pressure of war to change their choices. The mood here is calm and hopeful, with images of gliding, glowing white light and clear air.
Then the poem turns sharply. "Almost" signals that the freedom isn't going to last. A bullet hits the left wing, and the speaker's fear is physical: a numb body, a stomach "a ball of mush," sweat-soaked feathers. A second bullet hits the right wing, and the short, blunt lines ("They did it. / This is the end.") make the ending feel sudden and final. The dove, a traditional symbol of peace, is brought down, so the poem leaves us with a sense of helplessness and the sad idea that war can destroy even the wish to escape it.