Washington Post reporter T. Rees Shapiro is forced to crawl on his back with a brick-filled backpack on his belly during a GoRuck challenge. (Astrid Riecken/FOR THE WASHINGTON POST)

It’s 7 a.m. on the Fourth of July in Georgetown’s Montrose Park, and the sun is cresting above a group of 260 men and women standing at attention.

In front of them is former Marine Corps staff sergeant Chris Stokes, decked out in a chest-tight black tank top, tattooed biceps bulging.

For the next 12 hours, the group will be split into teams of 35 and led by combat-decorated special operations veterans on a march through the District. They will cover at least 15 miles while shouldering rucksacks loaded with 40 pounds of bricks. The teams also will hoist fallen trees and rocks the size of car tires. The temperature will peak at 89 degrees.

“You’re here to test yourself physically and mentally,” Stokes tells them. “At some point you may be the weakest person. At some point you may be the strongest. But it doesn’t matter. You’re only as strong as your weakest team member.”

Stokes stalks by the assembled ranks. Inked on his forearm is a winged skull and the Latin words “Celer-Silens-Mortalis” — “Swift, Silent, Deadly,” the motto of the Marine Corps’s elite Force Reconnaissance companies.

“You’ve got to dig deep,” he says. He gestures to the group of men a few yards behind him — all seasoned special operations veterans, mostly Army Green Berets who served tours in Iraq and Afghanistan during the past decade. “I guarantee you you’re going to have some good living today — some pain, suffering and misery that’s going to be served up by these gentlemen.”

A nervous energy zips through the participants, and some begin to question themselves. Later that day, tourists celebrating the holiday in the nation’s capital will stop the teams and ask: What are you doing? The answer is the GoRuck Challenge, a grueling test of endurance that offers participants “a day in the life of Special Forces.” The objective of the challenge is not to finish first. It’s to finish.

“You signed up for this,” Stokes says, seemingly sensing the apprehension. “Don’t quit on yourselves. Don’t quit. No matter what.”

And so begins one of the hardest days of my life.

Twelve hours of agony

The GoRuck Challenge gives civilians a dose of Special Forces training.

A former Army Special Forces soldier, Jason McCarthy, 34, founded GoRuck and modeled the challenge on the rigorous training he endured to earn the coveted Green Beret.

“The challenge is intense — it’s as hard as anything I had to do in the Army compressed into 12 hours,” McCarthy said. “It sucks.”

He started the event in 2010, when he was still in graduate school at Georgetown University’s McDonough School of Business. Since then, GoRuck has led more than 750 challenges across the country. More events are planned for Paris, Tokyo and Sydney. In four years it has gone from a company that took in slightly more than $50,000 in annual revenue to one that expects to bring in $12 million this year.

A veteran of the Iraq war, McCarthy sought to create an event that melded the military and civilian worlds, largely because “no one else was doing it.”

The goal of GoRuck Challenges, he says, is “to build better Americans” by bringing strangers and veterans together to overcome hardship through teamwork. It’s impossible for one person to lift a 1,000-pound log, McCarthy points out. But when a group of people pick it up, it becomes a shared burden that forges camaraderie.

Mark Webb, 41, has taken in part in 29 challenges — more than anyone. A software engineer in Manchester, N.H., the British-born Webb said he was hooked in 2011 after his first challenge in Boston.

“My favorite thing during a challenge is when someone is about to quit,” Webb said. “The team rallies together to get everyone to the end. Seeing that selflessness, I love it. It’s one team, one fight, till the end.”

I completed my first challenge in March. It was a lung-burning, leg-wobbling, heart-throbbing experience that left me incapacitated for two days. My shoulders ached from the weight of my brick-laden backpack, my feet had blisters, and the skin on my legs had been rubbed raw from the 20 miles we walked around the District. But within a few weeks my wounds had healed and I was hungry for more.

When I told friends I was signing up for a second challenge on the Fourth of July, most of them asked: Why? You did it once, so what do you have left to prove?

I thought about my motivations. I came of age in the post-9/11 era. I was a few days into my freshman year of high school when the twin towers fell, when the Pentagon burned and when the phrase “Let’s roll” came to embody our country’s fortitude.

As I sat in my high school classrooms in 2003, teenagers just a little older than I was rode Humvees through the desert to unseat a dictator. Although the Sept. 11, 2001, terrorist attacks have defined my generation, many of us have felt removed from the wars that followed. For thousands like me, GoRuck has helped narrow the divide. If only for a few hours — and far from an actual battlefield — the challenge offers a glimpse of the brutal regimen the elite troops must endure. For most participants, the day-long event is enough to satisfy the curiosity.

In the past three years, more than 17,000 people have taken part in a challenge. The event’s success is owed partly to the rise of other extreme endurance events such as Spartan Race and Tough Mudder, which bills itself as “probably the toughest event on the planet.”

In 2010, about 41,000 people took part in such obstacle races. Last year, more than 1.5 million signed up for them, according to Outside magazine.

Tough Mudder and Spartan Race have capitalized on the booming industry by offering cubicle jockeys a way to escape fluorescent-lit boredom by taking on courses featuring knee-deep mud, high-voltage electrical shocks and ankle-licking flames.

Justin Anderson, a sports psychologist in St. Paul, Minn., said people are drawn to extreme endurance events “to push their bodies to the maximum.”

“It’s that internal drive that humans have to grow and to push themselves,” Anderson said. “I believe it’s the same drive that pushed us to the moon. Humans do not do very well when they are just being still.”

Anderson said movies such as “Zero Dark Thirty,” the dramatic 2012 portrayal of the raid on Osama bin Laden’s Abbottabad, Pakistan, compound by Navy SEALs, has attracted people to events such as Tough Mudder and GoRuck.

“We’ve seen how challenging it is to go through the training and how even the most fit and highly motivated people struggle through it,” Anderson said. “I think everyone has that curiosity that says, ‘Could I do that?’  ”

But what’s next for those who have finished a Tough Mudder, or two, with ease? For some weekend athletes, the mud-run bubble has burst, and they are seeking new outlets, such as GoRuck, to slake their thirst for adrenaline.

Which makes GoRuck’s newest event, the Nasty, its biggest gamble. On Sept. 21, the company will host an expected 3,600 participants at the Massanutten ski resort outside Harrisonburg, Va., for its first foray into obstacle racing. The Nasty will be patterned on “Nasty Nick,” an Army Special Forces obstacle course at Camp Mackall, N.C., that all candidates must complete to don the Green Beret.

McCarthy said he envisions the Nasty as a semiannual reunion of sorts for GoRuck, an event akin to “Woodstock meets Special Forces.” Combat veterans will cheer on participants as they grapple with the 27 obstacles, including incline walls and tunnels, set out over a six-mile course.

Once racers finish, GoRuck will sell cans of beer for $1, with the proceeds going to the Green Beret Foundation, a charity that provides financial support for wounded Special Forces veterans and their families.

McCarthy said one part of the course will feature a memorial walk to honor special operations troops who have died since Sept. 11, 2001. To date, GoRuck and participants have raised more than $500,000 for the Green Beret Foundation. (McCarthy is the chief marketing officer for the charity; he works pro bono.)

McCarthy said the Nasty will be different from a Spartan Race, where the focus is on competition, or a Tough Mudder, where the company’s top-dollar sponsors such as Bic razors and Degree deodorant are omnipresent.

Whether the Nasty will succeed rests with McCarthy.

GoRuck founder Jason McCarthy. (Astrid Riecken/FOR THE WASHINGTON POST)

McCarthy wears one of his designed backpacks. (Astrid Riecken/FOR THE WASHINGTON POST)

A lanky 6-foot-4, McCarthy met with me in late June in his Georgetown condo to talk about GoRuck. Padding faithfully by his side was his chocolate Lab, Java, whose companionship McCarthy credits with saving his life after war and divorce.

Born in Kettering, Ohio, McCarthy says his work ethic came from his father, a union man who runs a printing press in Dayton. His athleticism he inherited from his mother, an All-American tennis player at the University of Florida.

His parents met as teenagers, and McCarthy was born a few days after his mother turned 18. They divorced when McCarthy was an infant, and he grew up in the Jacksonville, Fla., area.

McCarthy studied economics at Georgia’s Emory University, where he played on the tennis team and graduated Phi Beta Kappa in 2001. Pursuing a business career, he joined a marketing firm in Daytona Beach, Fla., and was on his way to work when he heard the news of the planes hitting the World Trade Center.

Compelled by the attacks, he joined the Army in 2003 as a Special Forces recruit. The training was hellish. Exercises included going three days without sleep and carrying a 100-pound rucksack for dozens of miles. He broke his nose and suffered a concussion during a parachute jump. He deployed to southern Iraq in 2007 as a communications sergeant with the 10th Special Forces Group, serving on Operational Detachment Alpha 042, a 12-man unit known as an “A team.” The soldiers spent most of their time training Iraqi police forces to battle insurgents.

One night, they received a call from their Iraqi counterparts, who were under attack from an overwhelming force of militants.

“We answered the call and went on a warpath,” McCarthy said. “I will never forget that night until the day I die.”

During the engagement, his team came under fire from a building not far from their position. Pinned down, McCarthy radioed an AC-130 gunship crew circling above, calling in “danger close” airstrikes. The building was blasted, silencing the gunfire. McCarthy was awarded the Army Commendation Medal for valor in action.

He left the Army in 2008 as a staff sergeant and moved to Ivory Coast to be with his wife, a diplomat at the U.S. Embassy in Abidjan. But long distance had eroded their six-year marriage, McCarthy said. He moved back to the States, despondent.

“The difficult part of being in the military was the strain on my family and personal life,” he said. “I got out of the Army with my marriage on the decline. It was humbling for somebody like me. It taught me a lot about compassion and humility. I didn’t accept it very well.”

He earned a full scholarship to Georgetown and began to devote time to his hobby: GoRuck. In Africa, he had formed a business in 2008 putting together “go bags,” filled with rations and other emergency supplies for expats and diplomats who might need to evacuate. The initial GoRuck business didn’t pan out, partly because McCarthy wasn’t happy with any bags available on the market.

So he set out to design a rucksack worthy of war zones, sketching out his ideas on a napkin. The result two years later was the GoRuck GR1, a bag handsewn in Seattle that comes with a lifetime warranty.

But the bag cost $295, and McCarthy had a difficult time persuading retailers to partner with him.

“I learned that the story mattered more than the bag,” McCarthy said. He began to write long posts on the company’s Web site about himself and his time in the Army. Still, he said,“nobody cared about the bags until I created the challenge.”

He held the first event in San Francisco in September 2010. Participants saw the durability of McCarthy’s bags firsthand as they carried the backpacks through mud, sand and ocean water. More events followed, and suddenly the business took off.

McCarthy devotes a majority of his time organizing challenges and other events, including the GoRuck Light, a shortened challenge and the GoRuck Heavy, a 24-hour version where participants aren’t allowed to sleep.

The challenge costs participants between $95 and $140. They “make money, but not a lot,” McCarthy said, and that has spurred the company to diversify its offerings.

As chief executive, McCarthy has started exploring new business ideas, such as corporate training exercises for executives that don’t involve bricks or sweat. (That operation, called GoRuck Solutions, is led by his former wife, Emily Dent.)

Last month, he opened the first GoRuck retail location in Florida, and he hopes to open one in the District in the next year. He plans to expand GoRuck gear with a new line of outerwear, including jackets and pants.

For now, GoRuck remains a small business, with 38 full-time employees. McCarthy takes pride in hiring combat veterans who have struggled to find employment.

“GoRuck gives special operations guys a gateway to reconnect with society,” McCarthy said. “It’s a place where they feel inherently welcome. Guys with multiple combat tours come up to me and say that they would have killed themselves if it wasn’t for GoRuck.”

After walking for hours, carrying brick-filled backpacks and heavy logs, GoRuck participants are assigned an additional set of push-ups. (Astrid Riecken/FOR THE WASHINGTON POST)

A heavy log rests on the shoulders of participants in Rock Creek Park. (Astrid Riecken/FOR THE WASHINGTON POST)

The Fourth of July Challenge begins with push-ups and flutter kicks. We hold our 40-pound bags above our heads and do squats. Within an hour I am drenched with sweat and exhausted, with 11 more hours to go.

My group is led by Michael Stewart and Bert Kuntz. Stewart was one of the Air Force’s combat controllers, elite commandos who can parachute into hostile territory and direct air traffic. Kuntz served in the Army as a Special Forces medic from 2002 to 2012 and spent about three years in Iraq.

“People have no clue what they’re capable of physically,” Kuntz says. “We’re getting people out of their comfort zone and pushing them to unlock their potential.”

Throughout the day, we would cover 15 miles. We set off from Montrose Park and walk the C&O Canal path to the Georgetown Reservoir. We come back through town and stop at the “Exorcist” stairs. Then we climb them twice.

When Kuntz notices that we have lost focus, he orders us to get in the push-up position.

“This isn’t a Fourth of July cookout,” Kuntz says. “This a GoRuck Challenge. ... You guys are walking around the nation’s capital on a beautiful day. But right now there’s a guy in Afghanistan carrying a 100-pound ruck waiting to get shot at, or getting shot at, at this minute.”

He lets the words sink in for a few more moments. My arms burn from the weight of my backpack. He orders us to get up and keep moving. We do, and I see that our team walks with more purpose now.

We head toward Roosevelt Island. There, we hop into knee-deep pools of water. At one point the group takes “casualties,” and we have to carry the wounded members of our team on our shoulders through the pools. I look over and see Manny Jimenez, 24, a single-arm amputee who has one rucksack on his chest, another on his back, and a person slung over his shoulders.

Then Kuntz stops us. We have moved too slowly, he says, and lack urgency while carrying our casualties to a nearby evacuation point.

“Raise your hand if you have ever served in the military,” Kuntz says. About four people in our group of 35 raise a hand.

“Keep it raised if you’ve ever served in combat,” he says. Two hands stay up.

“Raise your hand,” Kuntz says, “if you’ve ever been wounded in combat.”

Jimenez, who has rarely spoken during our challenge, keeps his only hand in the air. A former Marine corporal, Jimenez deployed to Marja, Afghanistan, in June 2010 as a machine-gunner. Two months later, his unit was returning to its command post when a 40-pound makeshift bomb exploded a few steps away from him.

“I thought, ‘Man, they got me,’ ” Jimenez tells me after the challenge. “I hit the ground, felt my arm and felt hot liquid all over it.” His left arm was later amputated at the shoulder.

Kuntz points out that Jimenez is the only member of our group hustling to get our wounded out of the pools.

“Manny knows that in combat, every second counts,” he says. “He knows that when one of your buddies is in need, you keep moving.”

As I carry a “wounded” comrade over my shoulders, my head throbs from the heat and the heft of his body. My chest heaves as I search for air. I think about what Kuntz said and look at Manny for inspiration. I refuse to put my wounded buddy down until my knees buckle and I almost collapse to the ground.

Later we march back across Key Bridge and head north through Rock Creek Park. We then wade into the creek, do push-ups in the silty shallows, and emerge with sand and grit in our socks. Throughout the day, we would complete more than 150 push-ups. By the end, my arms hang from my shoulders like damp laundry on the line.

We hike our last mile sopping wet, arriving in Georgetown at 6:30 p.m. Back in Montrose Park, each of us receive the GoRuck Tough patch, signifying our successful completion of the challenge. McCarthy says the patch will never be for sale. The only way to get one is to earn it.

We have been beaten but not broken. We have worked as a team and finished together. Nobody quit.

T. Rees Shapiro is a Washington Post staff writer. Send e-mail about this story to wpmagazine@washpost.com.