Marines who fought the North Vietnamese Army weren't interested in God, country, and Mom's apple pie: They were focused on fighting for a cause that was never fulfilled.

Thomas Hynes, a Marine Corps second lieutenant who led the 2nd Platoon, Lima Company, Third Battalion, Fifth Marines, looks back at the challenges he faced undertaking his first command. He quickly learned that the North Vietnamese Army was far more capable to fight in the jungles and mountains.

But that didn't stop young Marines from fighting for their country and each other--even though it resulted in...