Machine-gun fire erupted at the top of the hill, where a soldier in camouflage face paint hid behind a rock pile. I could barely see him through the smoke in my eyes, which I mostly kept fixed on the muddy ground so I could concentrate on carrying the two 30-pound metal cans of ammo up the slope. My legs were burning, my lungs were heaving, and I was pretty sure there was blood running down my arm.

South Vietnam? Nope. But this endurance race, the 2012 Walter N. Levy Challenge, was designed to re-create some of the challenges that its namesake, a Norwich University student, faced in Quang Nam Province before he was killed in action in September 1965. When Norwich race organizers decided to open the grueling event (held this year on September 22) to the public for the first time, I couldn’t wait to start. But as I took on the “Rock Pile ammo resupply mission,” I was wondering if I’d ever finish.

Truth be told, I’ve never had a thing for messy obstacle races. Yes, I know they’re popular: A half million people are now racing in Tough Mudders, according to the 2012 “Obstacle Course Racing: State of the Union” from obstacleracers.com; 700,000 participate in the Warrior Dash series; thousands of others sign up for the Vermont-based Spartan Race series. And, yes, I know these races can be fun, emboldening, childlike, liberating and all that. But I’ve fallen on smooth pavement on a perfectly dry, sunny day and permanently scarred my chin. I’ve fallen off a treadmill. Twice. So the last things I need in my running path are deliberate obstacles.

Still, after crossing into a new decade and spending a few months working out at South Burlington’s new CrossFit Threshold Training, I was curious to see how my fitness stacked up against that of young marines. And I was eager to check out the natural obstacles that race director Capt. David Castro of the U.S. Marine Corps described. “It’s a great place to host a race,” he told me.

In the past, the Levy Challenge has been held in winter among teams of four vying to prove themselves the toughest on campus; the course has stretched as long as 16 miles, with additional elements in the campus swimming pool. “When there’s 5 feet of snow, it limits the terrain,” said Castro, who added that he changed the Levy’s course, date and length to give the public a chance to support the military (registration proceeds go to the Semper Fi Fund and a Navy Reserve Officers Training Corps scholarship). As he put it, “What better way to support something worthy and patriotic than by being physically challenged at the oldest private military university in the country?”

From the packet that I received from Capt. Castro a few weeks before the event, I learned that this year’s race was 6.5 miles. Definitely doable! I was also encouraged to see that the Levy Challenge was presented by the Knotty Shamrock, a pub in Northfield. How bad could a pub-sponsored race be?

But then I read that I was supposed to wear a long-sleeved T-shirt to “prevent any elbow abrasions,” and sturdy cargo shorts to negotiate “multiple low-crawling sections” and climbing walls. My clothes, the packet promised, would become “muddy, torn, frayed.”

My nerves were what felt frayed after I glanced over the racecourse description — including “worm pits” — and checked out the waiver that described “risks of serious bodily injury, including permanent disability, paralysis and death.”

On race morning, I showed up at Norwich’s Plumley Armory an hour before my start time of 8 a.m. In my nectarine-colored GoLite shirt and black lululemon capris, I stood out like a sore thumb among the hordes of “rooks,” or Norwich freshman, wearing full camo and CamelBaks.

Of the 250 entered in that day’s Challenge, I later learned, the majority were rooks or active members of the military. Many were still upholding tradition in teams of four. Carrying heavy, awkward objects, crawling through muck, doing pull-ups and lunges? All in a day’s training for most of these folks. Paper race bibs? Those are for wimps. We were given permanent-marker numbers on our arms, cheeks, foreheads and legs.

To quell my anxiety near the starting point at Sabine Field, I chatted with Brian Tarbox, a 28-year-old Norwich grad and Barre-based architect who does Tough Mudder and other races to stay in shape. Buying a croissant for her 9-year-old daughter and stretching for the race was Ana Delvalle, a 4-foot, 11-inch, 30-year-old marine of Salvadoran origin who’d decided to test her Victoria’s Secret makeup spray by wearing it today. Badass. Then there was the quartet from the U.S. Coast Guard Academy, who told me they’d been training by running with rucksacks in full gear, doing buddy carries and climbing walls.

Gulp. But before I had time to beeline it back to Burlington, Capt. Castro was playing the national anthem and giving us the countdown. Waves of eight participants were released every two minutes, and Delvalle and I sprinted 100 meters to the first station, where it was 10 pull-ups for men, 10 burpees for women.

I hate burpees. Little did I know that in about one minute, I’d be burping up mud after crawling through a Dog River swamp. The gunk got caked to my capris, making the mile-plus climb straight up Hill 488 even more arduous.

But, somehow, I was channeling Levy himself — and by refusing to walk, I’d taken the lead in my wave. On the exhilarating run back down the road, I braced myself for the Da Nang serpentine: a poisonous, snaking course of stutter-step tires, long jumps, water-jug carries, railroad-tie pushes and the like. Thanks to some marine-driven motivation, though, it was manageable — and, as tough as the challenge was, I was repeatedly struck by the kindness of the 45 volunteers. One even sought me out to hand me a cup of water when none was available at a Gatorade station.

Things were not so sweet when I had to carry a 30-pound sandbag down a seemingly endless trail. My quads and back were screaming, I slowed to a walk, and by the time I reached the portion of the race I’d dreaded most — the Quang Nam worm pits — I was so delirious with the relief of dropping the sandbag, I didn’t mind writhing in the cool mud with a fire hose spraying in my face. (There weren’t actually worms, after all.)

Because of my lollygagging with the sandbags, Delvalle and another woman — 19-year-old Delaney Welch, I would learn later — were catching up to me. So I forced myself to run through the tire carry, up and down and up and down a hill, and round and round stakes until I was thoroughly dizzy. Then came the U.S. Marine Corps obstacle course, also known as the O Course or, for me, the “Oh, shit” course: I uttered plenty of curse words and cries of “Are you kidding me?” as I attempted to fling myself up a wall and over chest-high and head-high logs.

At this point, the race packet promised “a trip into the jungle.” Um, sure, if that jungle was something out of Apocalypse Now. The Rock Pile ammo resupply, I feared, would be my Waterloo. But I completed the task and made it to the Upper Parade Deck, where I picked up an M16 rifle, and the straps of my 50-pound field pack promptly broke on my back.

“My pack!” I cried out. I was suddenly the hunchback of Norwich University lurching around the prestigious green.

Not pretty, and neither was the moment when I flew across the finish line holding the M16 upside down and backward like a crazed lunatic. I was muddy, I was scraped up, and I was a bit bruised, but I was alive and delighted to see a table full of PB&J sandwiches, oranges and bananas.

I savored the sight of racers coming in, equally begrimed and beaming. Eventually, results sheets were posted, and I learned that my time of one hour, 15 minutes and 58 seconds had earned me the title of “first female individual.”

My prize: Spray painted with the words “2012 Walter N. Levy Challenge,” and mounted on a wooden board was — what else? — an ammo can.