Just because a poem is short, that doesn't necessarily mean it has less going on in the sound department than longer poems. Just look at our friend the haiku—only seventeen little syllables, but sound often plays a big part.
Here are some ways sound is working in "The Death of the Ball Turret Gunner":
First up, we have alliteration. The F sounds a the end of line 2: "fur froze." The sound echoes the f-f-f-f-f sound we make when we are chattering cold.
Next, try this: say, "black flak" ten times. Really, go ahead, no one's listening. Fun, wasn't it? Well, we have internal rhyme to thank for that. Those harsh, repeated, rhyming sounds in line 4 mirror the sound of machinegun fire or the explosions that the gunner was hearing during battle.
Of course, this poem doesn't have a regular rhyme scheme, but the end words of lines 2 and 5 do rhyme. This makes a very strong auditory connection between the two lines of the poem that include the womb/birth imagery. Randall wants to make sure we connect that "belly" in line 2 with the "turret" in line 5 and he relies on sound to make that happen.