This is a poem about being haunted and the aftermath of the war. In the last stanza the poet remembers the girl that tried to run away after the Napalm was dropped and she was hit:
she is burned behind my eyes
And not your good love and not the rain-swept air
And not the jungle green
Pasture unfolding before us can deny it.The poem ends by reminding the reader that the events of the war are forever etched into memory, "behind my eyes", and nothing can bring relief from the memory. I suggest if you are attempting to go the interpretive route with your essay, you could argue in your thesis that the traumatic memory of the Vietnam war can't be erased by time or the return to a normal life. The poet reiterates that in other lines as well :
So I can keep on living,
So I can stay here beside youfor instance. Regarding your our question of poetic devices, remember that this is a free verse poem, so there is no rhyme scheme in particular, but the form of the free verse lends itself particularly well to convey the brutality of the act the poet witnesses-the dropping of the Napalm. Form thus matches content. The poem also works with similes. E.g.
Trees scraped their voices into the wind, branches Crisscrossed the sky like barbed wireYou also see in this line that the poem carries sentences over ("branches" could have appeared in the next line since it comes after the comma). This technique prevents a feeling of closure, which is what the poet reiterates in the last line for instance. The line above also illustrates a personification ( trees scraping their voices). Literally, the world is coming alive around the soldier, and not in a good way. Finally, fire in literature is quite often a very romantic motif, but this changes with literary accounts of the United States annihilation of Hiroshima and Nagasaki at the end of WW II and the trauma of the Holocaust where burning became a metaphor for the wholesale destruction of the Jews. In the poem, the fire is caused by Napalm and the girl is literally burned alive before the eyes of the soldier. Fire is thus connected not only with destruction and burning alive, but also with forced witnessing and the creation of unerasable traumatic memory.