Trauma and violence
The memoirist begins by reflecting on a thematic irony: the difference between what he expected war to be about and what it actually was. See, to him as a youth, the Marine Corp represented sacrifice, and honor, and rightly so, because that institution is well-known for those things, but that doesn't mean war is not horrific. This story is the first person account of a veteran of Vietnam, a real combat warrior who witnessed the Fall of Saigon. He sets the tone with an introduction about his innocent opinions before the war, but the reality and trauma of those horrific battles are what fill the pages.
Esoteric agenda
The reader might need to know this detail to understand this theme. After Vietnam, many veterans were despised by those who opposed the war. So, without blaming the government, Caputo responds to that public scrutiny. The reason he says that veterans should not be held accountable for the decisions in a war is that when he was deployed, he was often not given very much detail about a mission. His case study for this point is the passage about "defending" the Da Nang airstrip. No one told him anything except what pertained to his military duties.
Responsibility
Although his account defends him and other veterans from those who would potentially blame the veterans themselves for the horrors done in Vietnam, he also points out that scrutiny is well deserved. When two of his men commit murder out of personal hatred against Vietnamese people, he claims responsibility for that happening on his watch. That is how committed he is to responsibility, and yet, he was judged to be innocent. He remembers that many people committed abominable actions and that often, leadership was licentious and indulgent.
