Da Nang
Lt. Caputo has a symbolic experience of Da Nang, because his orders were simply, "Defend the airstrip in Da Nang," but when he went to execute the orders, the "defense" part was like a cruel joke: There were so many enemies that he was perplexed. Why on earth would they give such misleading instructions? This symbolizes the limitation of his moral duty at war: He doesn't know all the facts about the Vietnam War, because he's participating without complete understanding.
Saigon
Saigon epitomizes the problems in Vietnam, and Lt. Caputo has to watch it play out in front of his naked eyes. He watches his men be slain by an enemy that is so skillful and masterful in their domain that all the training in the world could never make a person truly "safe." With tunnel routes and private pathways through deep jungle, the Americans are simply defeated.
The archetypal warrior
There is an archetypal relationship between the memoirist and his home. He returns to his life like Odysseus after his Odyssey, to find that life back home is not suited for war heroes, but for regular civilians. Without anyone to understand his suffering, he is forced to accept public scrutiny and blame for a war that he didn't ask to witness, but he did witness it. He is a true hero in the Greek sense of the word, a would-be martyr of human warfare.
The death counter
Adding even another layer to the abstract quality of Lt. Caputo's experience of war is his strange assignment of documenting the dead and missing. As a literal death counter, he is asked to know about real instances of human death in Vietnam. He is a witness to these deaths, literally and symbolically, and where other people know statistics and figures, he knows names and dead bodies.
Torture as the symbol for human evil
Two instances of torture are mentioned: There is the chronic instance of torturing Vietnamese prisoners of war without respect for human dignity, and there is the deliberate assassination of two Viet Cong POWs under his watch, prompting him to take responsibility for his platoon. However, he notices how evil and horrific these actions are, pointing to torture as the sign of human evil. Some people were in Vietnam to kill people they hated, not to do war for their country.
