The young captain saw war as man’s ultimate competitive sport. It was this realization that brought James Estep back to Vietnam for a third tour — this time as a company commander in the famed 1st Cavalry Division. Call-sign “Comanche Six,” he commanded an airmobile rifle company. They were pawns in this game of war: picked up by helicopters and dropped off at an LZ in the heart of “Indian country,” with orders to launch search-and-destroy missions by day, and “trick or treat” patrols at night — to find the elusive “Charlie” and kill him. Vietnam has been called the “company commander’s war” — these were the young officers who ran the war on a day-to-day basis, making life and death decisions in the jungles, rice paddies, and villages. Estep quickly...