Gearhart's the man who replaces Lieutenant Carroll after he dies. Big shoes to fill already, and what's worse, he seems like a terrible replacement. He's not naturally the kind of leader who cares about his guys—he's not the friendliest pea in the pod, and at one point he even forces the platoon into a vulnerable position just to show his authority over Simpson.
Then he accidentally sends off a flare that gives away their position, which gets a guy killed. Rookie mistake.
On the plus side, it humbles him, big-time.
He writes a very guilty letter to the dead soldier's family. Perry even has to rewrite because it's such a mess. (Not the most comforting to read about some lieutenant's guilt, not about your lost family member, after all.)
Gearhart takes a backseat to Simpson after that, staying quiet and letting Simpson call the shots. And later, when he takes a few men out on patrol, he shows that he's actually not such a bad leader. He makes his men hold off on firing at a couple Vietcong soldiers, sensing that there's a battalion behind them. He's right.
"How did you figure out there were so many?" Walowick asked.
"They were talking too much," Gearhart said. "Too confident."
If it had been me, I thought, I would have screwed it up. I would have. (15.75-77)
Way to go, Gearhart. If not for his instincts, the men might have given away their position, gotten overwhelmed by being outnumbered, and been killed. That's definitely worth something.
In the end, Gearhart's not so bad. He's no Lieutenant Carroll, but he's no Mr. Magoo either.