You can find heroes in any war, and they are usually the first ones to tell you that they don't consider themselves heroes. In O'Brien's novel The Things They Carried, the author lets the reader decide what heroism was, and who best exemplified it.
If you take, for instance, the part of the story where they are drawing numbers to see which one of them gets to play "tunnel rat" for the day and crawl underground searching for Vietcong. Are any of the men heroes? Strunk draws the number which makes it his turn, and he does his duty, but was it because he was a hero? Or just unlucky? He then emerges alive and unhurt, but does this make him brave, or just lucky?
The idea about heroism I walked away from the book with was that every soldier who showed up and went into the field in that story had the character of a hero. Sometimes it was revealed, and sometimes not. Some were more heroic on one day than the next. And some were merely unlucky, killed by a sniper while returning from going to the bathroom. Having involuntarily sacrificed his life in such an unremarkable manner, was Ted Lavender less a hero? No way. His name is on the Vietnam wall in DC just like the rest. I think this is one of the things O'Brien was trying to tell us.
O'Brien debunks male heroism in the novel. In "On the Rainy River," he admits, "I was a coward, I went to war." He feels extreme guilt in "The Man I Killed" and "In the Field" regarding Kiowa's death.
Instead, he idealizes the role of females as his ideal audience and, mythologically, as superior warriors (Mary Anne Bell) in the story "The Sweetheart of the Song Tra Bong."
Tim O'Brien revisits the female warrior, albeit an American, in Mary Anne Bell, a seventeen year-old "blonde"..."kid"..."barely out of high school" who arrives in Vietnam wearing "white culottes and a sexy pink sweater" (O'Brien 90). By the story's end, she becomes a phantom Green Beret assassin wearing a "necklace of human tongues," "dangerous" and "ready for the kill," a transformation that, according to the civilian reader seems overly-dynamic, but in the context of Vietnam war mythology seems plausible.
It is my contention that O'Brien intentionally writes Mary Anne's story so full of fantasy that her transformation cannot be rationalized by the (male) reader as much as intuited by the female (or at least androgynous male) one. Intuition implies the spiritual, and Mary Anne's conversion is certainly a mystical one, as she becomes the prototypical warrior, an uncommunicative male who lives only for the hunt.