Buffalo season closed at dusk on New Year's Eve. "The dumbest buffalo in Arizona just outwitted me for ten days," I observed as our final campfire of 2001 held back the deepening snow. Though nobody in our party spotted the elusive timber-dwelling bison of the Grand Canyon's North Rim, we still celebrated a memorable hunt. I heralded 2002 guessing that I'd soon trade my .300 Winchester for an M16. The world had changed in the months since I'd drawn my coveted tag: America had been attacked, and now it was payback time.

A week later, I was called back to active duty in the Marine Corps. Fifteen months after that, I led 21 machine gunners during the liberation of Baghdad. Along the way, I needed expertise in firearms, optics and off-road vehicles. I needed navigational skills and physical stamina. I needed to locate my opponents by thinking like them. Above all, I needed to prevail without breaking the rules. In short, I needed to be a hunter.

The parallels between hunters and infantrymen begin with our shared tools: firearms, optics and navigation equipment. During our first year at Camp Pendleton, Calif.""painfully, the home to large buffalo herd""the best hunters in my platoon showed themselves to be the most proficient Marines. The Corps teaches marksmanship under controlled conditions on known-distance courses, but rarely makes us estimate distances or prioritize targets""the exact skills needed on the battlefield. They familiarize Marines with optics, but don't practice systematic searches with binoculars. They teach antiquated compass-based navigation. Before leaving for Iraq, I drilled my men in range estimation and terrain association, and I "suggested" that they buy and master GPS units. In combat I was one of the few men who knew where I was at all times, which direction I was facing, and approximately how far away any enemies were. During a firefight in Baghdad, our reinforced platoon of 60 men was moving to link up with the rest of the company. I was the only one actively monitoring my GPS, and quickly realized we were heading the wrong way. I got the column turned toward the proper rendezvous point, where the enemies shooting at us were the intended ones, at least.

I've always sought challenging hunts on roadless terrain with scattered game. Arizona Game & Fish named my buffalo hunt "one of the most difficult hunts in the state." This was small consolation for the missed opportunity, but good preparation for the Corps. Though nearly the oldest man in my unit, I kept up with the young guys during a 27-mile march with 75-pound packs, and I scored highest in physical fitness. Our three-week push to Baghdad joined stupendous mud and sandstorms with hunger and sleepless nights. Baghdad tested my physical limits, as I sprinted across intersections under heavy fire, wearing full armor and lugging belts of ammunition. Without years of rigorous conditioning, I might have been a step too slow at the wrong time.

Hunters are used to failure. Most of my hunts end as my buffalo hunt did, just as most of my casts end without a trout on the line. All hunters and fishermen appreciate that unsophisticated creatures on their own terrain often outsmart the savviest outdoorsman. This makes us think like our opponents, continually reevaluate our weaknesses and learn from more successful sportsmen. The buffalo hunt taught me to walk less and glass more. In Iraq, this was equally useful against Saddam's Fedayeen militia. These irregulars lacked sophistication but understood deception, and were as hard to spot as an Arizona whitetail. I owe my life to the best hunter in my platoon, who spotted an enemy observer directing fire at us. Dressed as a civilian, the enemy observer continually peered out with binoculars from behind a wall, then disappeared again, at which point bad things always happened.