Several days after they arrived, O'Byrne's platoon went on patrol with men from the 10th Mountain Division, whom they were replacing in the valley. Tenth Mountain had begun their rotation back to the United States several months earlier, but Army commanders had changed their minds and decided to extend their tour. Men who had arrived home after a year of combat were put on planes and flown back into the war. Morale plunged, and Battle Company arrived to stories of their predecessors jumping off rocks to break their legs or simply refusing to leave the wire. The stories weren't entirely true, but the Korengal Valley was starting to acquire a reputation as a place that could alter your mind in terrible and irreversible ways.
However messed up 10th Mountain might have been, they'd been climbing around the valley for over a year and were definitely in shape. On the first joint patrol they led Second Platoon down toward the Korengal River and then back up to a granite formation called Table Rock. Tenth Mountain was intentionally trying to break them off make the new men collapse from exhaustion and halfway up Table Rock it started to work. A 240 gunner named Vandenberge started falling out and O'Byrne, who was on the same gun team, traded weapons with him and hung the 240 across his shoulders. The 240 is a belt-fed machine gun that weighs almost thirty pounds; you might as well be carrying a jackhammer up a mountain. O'Byrne and the rest of the men had another fifty pounds of gear and ammunition on their backs and twenty pounds of body armor. Almost no one in the platoon was carrying less than eighty pounds.
The men struggled upward in full view of the Taliban positions across the valley and finally began taking fire halfway up the spur. O'Byrne had never been under fire before, and the first thing he did was stand up to look around. Someone yelled to take cover. There was only one rock to hide behind, and Vandenberge was using it, so O'Byrne got behind him. 'F**, I can't believe they just shot at me!' he yelled.
Vandenberge was a huge blond man who spoke slowly and was very, very smart. 'Well,' he said, 'I don't know if they were shooting at you...'
'Okay,' O'Byrne said, 'shooting at us...'
Inexperienced soldiers are known as "cherries," and standing up in a firefight is about as cherry as it gets. So is this: the first night at the KOP, O'Byrne heard a strange yammering in the forest and assumed the base was about to get attacked. He grabbed his gun and waited. Nothing happened. Later he found out it was just monkeys that came down to the wire to shriek at the Americans. It was as if every living thing in the valley, even the wildlife, wanted them gone.