Combat in Vietnam was different from that of any other war in which the United States had fought. The Vietnam War was a guerrilla war, full of ambushes that usually started without warning. A rifle shot, a blast from a machine gun, or a booby-trapped trail was enough to start a minibattle between the opposing forces. Before the beleaguered troops could figure out where the enemy was hiding or how many there were, the attackers had slipped away into the jungle. Most firefights were short, usually ten minutes or less. Battles that lasted an hour or more remained unforgettable. Any fighting that persisted longer than a day was deemed a "major engagement"; battles that lasted even longer were highly unusual and considered epic.

American troops were not accustomed to guerrilla warfare, and most were not properly trained to fight against an invisible enemy. Most second lieutenants...