Right from the start, Jarrell confronts the reader with ideas and images of war: death and the gunner. How does all the war and death in the title work with the poem's first line? Does it conflict with anything, any word, in particular? (Hint: if you said mother you're onto something.)
The poem relies on the juxtaposition of the nurturing, protecting, life giving mother with "the State" to show the state as something that breeds death rather than life. By making the title so full of war and death, "mother" in line 1 gets emphasized. With the comparison between Mom and the State in place, Jarrell can build on it throughout the poem.
Six miles from earth, loosed from its dream of life, I woke to black flak and the nightmare fighters. (3-4)
More sights and sounds of battle, and lots of repeated K sounds mirroring machine gun fire or explosions.
Now, take a look at line 3. Notice any opposites? "Nightmare" (negative) in line 4 seems like the opposite of "dream" (positive) in line 3. These opposites and conflicting words and images that keep popping up miror war in some sense. A war takes two sides. War itself is the opposite of peace. War is a destructive rather than creative force. See? Opposites, opposites, opposites.
When I died they washed me out of the turret with a hose. (5)
The word washed generally seems pretty positive. It brings to mind clean laundry smells and is the opposite of dirty or unwashed (negative). But put "washed" into a phrase like "washed out" and suddenly things change. "Washed out" brings to mind something faded and worn or even a pale complexion, perhaps due to exhaustion or sickness. Not good. There is also the sense of a stain that has to be washed out of something.
When we add "me" (the gunner) to the mix, things get even bleaker. Here again, things start out sounding sort of positive. "They washed me"sounds kind of like a mother washing a baby. Nice. True, the line does begin with "When I died," so positive readings might be a reach. But even taking into the account the death, the washing of the body could still be positive in the sense of a final, loving gesture, part of some ceremonies and rituals dealing with death—washing the body before burial. But the addition of one little word, "out," changes everything. "They washed me out of the turret with a hose," seems especially cold and unfeeling—like the gunner's death is no more significant than a stain.