They shared the weight of memory. They took up what others could no longer bear. Often, they carried each other, the wounded or weak. (The Things They Carried.39)
Right here at the beginning of the book, we see that the brotherhood among the men is shared by all. Not only are they almost always referred to collectively rather than individually in this chapter (as "they" instead of by their names), but they also carry each other, emotionally (sharing "the weight of memory") and occasionally physically.
How to Tell a True War Story
The whole platoon stood watching [Rat shoot the baby water buffalo], feeling all kinds of things, but there wasn't a great deal of pity for the baby water buffalo. Curt Lemon was dead. Rat Kiley had lost his best friend in the world. Later in the week he would write to the guy's sister, who would not write back, but for now it was a question of pain. [Rat] shot off the [water buffalo's] tail. He shot away chunks of meat below the ribs. (How to Tell a True War Story.72)
The consequence of one soldier forming a close bond with another, Shay says, is that one of the two might die. If that happens, that death can trigger a berserker phase in the remaining soldier. Berserker phases have a lot in common with what Rat is doing now: wanton, senseless killing.
Rat pours his heart out. He says he loved the guy. He says the guy was his best friend in the world. They were like soul mates, he said, like twins or something, they had a whole lot in common. (How to Tell a True War Story.5)
According to Jonathan Shay in Achilles in Vietnam, one of the more unexpected problems that men face in war is that they tend to form incredibly close bonds with other men. But because of the anti-emotional machismo expected of soldiers, it's hard for them to explain how important those friendships are to people back home.
Rat's trying like crazy here—he says that he and Lemon were soul mates, that he loved him, and then finishes, lamely, by saying that the two had a lot in common. Um, right. Unfortunately, Lemon's sister doesn't get how important he was to Rat, and doesn't even write back.
The Man I Killed
"I'll tell you the straight truth," he said. "The guy was dead the second he stepped on the trail. Understand me? We all had him zeroed." (The Man I Killed.31)
Out of friendship, Kiowa is shifting some of O'Brien's guilt about killing a man onto himself (and the rest of the platoon). This calls back to the first quote we discussed here; the soldiers "shared the weight of memory."
Speaking of Courage
And a pity about his father, who had his own war and who now preferred silence. (Speaking of Courage.61)
You'd think that Bowker's father, as a former soldier himself, would be part of the brotherhood of soldiers. It looks like World War II (the most likely war for Bowker's father to have fought in) was traumatizing in its own right, if Bowker's father can't bring himself to speak about it. Still, his experience in World War II is clearly not enough to make him recognize his son's desperate need to communicate.
In the Field
He pictured Kiowa's face. They'd been close buddies, the tightest… (In the Field.49)
While Rat reacted to Lemon's death by going berserk, O'Brien reacts to Kiowa's death with denial. The first time we hear about Kiowa's death, O'Brien put the blame on Norman Bowker's soldiers. This time, when he's finally acknowledging both how close he and Kiowa were and his own responsibility in Kiowa's death, he has to use the third person. To use the first person would be too close, too painful.
The Ghost Soldiers
"[Jorgenson]'s with us now."
"And I'm not?'
Sanders looked at me for a moment.
"No," he said. "I guess you're not." (The Ghost Soldiers.198)
The bonds of combat only really last while the soldiers are in combat. No matter how inept Jorgenson was at the beginning, he's become a member of the tribe, while O'Brien, who's in a cushy position at the rear, no longer is. This is true even though Jorgenson joined the group way after O'Brien did. It has nothing to do with seniority and everything to do with being part of the fighting group.
You know you're about to die. And it's not a movie and you aren't a hero and all you can do is whimper and wait. This, now, was something we shared. I felt close to him. It wasn't compassion, just closeness. (The Ghost Soldier.154-6)
O'Brien forces the same knowledge on Jorgenson that he had to endure when Jorgenson freaked out instead of treating his wound. Once he's done that, once they've both felt the same fear of death, O'Brien is able to feel close to Jorgenson, and therefore accept him as part of the Alpha Company.
You make close friends. You become part of a tribe and you share the same blood—you give it together, you take it together. (The Ghost Soldiers.9)
After O'Brien's been sent to the rear, he reminisces about the war in the boonies. Again, we can sense the inadequacy of the word "friendship" to describe the way the soldiers feel about each other. They're not just friends, they're part of a tribe—blood brothers.
He was sitting there with Dave Jensen and Mitchell Sanders and a few others, and he seemed to fit in very nicely, all smiles and group rapport. That was probably what cinched it. (The Ghost Soldiers.111-2)
The final thing that pushes O'Brien over the edge, that makes him go through with his revenge plan, is that Jorgenson fits with the group now and O'Brien doesn't. It infuriates O'Brien as much if not more than the original crime of not taking care of O'Brien's wound properly.