MILLINOCKET, Maine — Kevin Reed once thought of himself as shy. His fear of rejection, he says, sat him back on his heels. He made you come to him, and when you did, he’d make sure you knew whenever he felt slighted. About anything.

His relationships were messy — divorce, an alienated daughter, bouncing from job to job as he sought a useful place in the world. Today he’s a truck driver. He spends his days alone, watching America slide by his windshield and under his 18 wheels.

The 43-year-old wasn’t always sullen. A U.S. Marine, fellow Leathernecks called him “Private Smiley.” He loved his life in the Corps. Reed understood how the service worked, how he fit into it, and how to get ahead within its blizzard of requirements and customs. He fought in Operations Desert Shield and Storm and locked away many of those experiences, he says.

“It was combat,” Reed said. “I don’t even try to compare my experiences with anyone else’s. Some people [experienced] what I did over there and go, ‘Eh. No big deal.’”

Speaking Saturday to about 75 fellow servicemen and hikers at the American Legion, Reed was nothing resembling shy. Animated and voluble, the Minnesota resident told inside jokes, and dispensed handshakes, hugs and anecdotes of his just-completed 2,185-mile trek up the Appalachian Trail from Georgia.

He plans, he said, to load into his truck’s GPS system the 250 to 300 pictures of wildflowers that he took during his six-month hike.

“At the beginning, somebody wanted to call me ‘Grumpy Grape’ as my trail nickname. I was told, look for something every day on the trail. It started out as me looking for the prettiest thing I could find,” Reed said. “Just knowing that they will be there [on the GPS] adds a certain level of comfort. It gives me something to look at and be happy about.”

Reed has walked off his war.

That’s the idea behind the “Walk Off The War Program” created by Warrior Hike, a nonprofit organization that has partnered with the Appalachian Trail Conservancy to host hikes of the entire trail by U.S. veterans, said Sean Gobin, founder of Warrior Hike. Many of them are combat veterans.

“Walk Off The War” is what World War II veteran Earl Shaffer told his family and friends he was going to do when he set out on the Appalachian in 1948. Shaffer was the first person history records as having through-hiked the trail. When he founded his program in 2011, Gobin named it after Shaffer’s explanation in recognition of the trail’s healing power, he said.

“They come to us with PTSD, depression, loss of purpose, a jaded view of humanity,” Gobin said of the veterans, “and they come back a reborn person, with an appreciation of life and a sense of humanity. That’s generally how it works.”

That might sound like a big bill to fill, but imagine walking rugged terrain, 12 hours a day for six months, with nothing to think about but your past experiences and the 10 feet of trail in front of you. It is a grueling and cathartic experience even for those in great shape, said Rob Carmel, a 50-year-old hiker and retired U.S. Army sergeant major, who served in Afghanistan and Iraq with a field artillery unit.

Fourteen hikers began this year’s trek, the program’s second. Six finished. Some dropouts suffered the injuries that come with the rigors of through-hiking. Others, Gobin said, saved a lot of money for the trip, did a lot of research on the trail and discovered a few weeks into it that they hated hiking.

The trail is often so rough that “you look down. You concentrate on the 10 feet in front of you, and it’s 10 feet at a time the whole way,” Reed said.

The endurance required for through-hiking surpasses that needed for any other activity, Carmel said. It’s an act of exertion but also self-preservation. A chronic pain, or a single misstep that causes injury, can end the journey, and hikers who cannot connect with nature will not see the end of the trail.

“It’s been harder than anything I have ever done,” wounded veteran Steve Clendenning said of the hike, “and that’s after 20 years in the Marine Corps, in the infantry.”

“I didn’t know it would be as challenging as it was,” Carmel said. “I had no idea what I was getting myself into.”

“You are on an emotional roller-coaster the entire time,” Gobin said, “because [hiking the trail] forces them to process what they have been through. You get days when you are angry, when you are frustrated, when you are laughing and full of life, when you think of the days where you lost someone.

“At the end of it,” Gobin added, “you have been through the emotional wringer.”

Through-hiking offers vast compensations, Gobin said. Other hikers provide socialization and support. Hikers lose weight. Food tastes better. They can eat as much of anything they want and still get slimmer. They yield to nature, withstand its elements, but can discover its riches and mysteries.

Wildflowers amazed Reed.

“When we started the hike, it was March, and everything was dead,” Reed said. “It was not long after that that flowers started blooming. Pretty soon they were all over the place, and they come up out of, like, nothing.”

Gobin developed the idea of hiking as catharsis from his own experiences as a Marine Corps captain in Iraq in 2003 and 2005 and in Afghanistan in 2011. Trained to behave as all soldiers must in combat — to switch instantly from normal to life-and-death situations — Gobin said he found himself back in the U.S. within days of leaving the combat zone.

Created by modern transportation, that sudden transition is partly responsible for what Gobin called the epidemic of post-traumatic stress disorder among combat veterans.

“The military has not cracked the nut yet on how to craft that transition process into something healthier,” he said.

Not that he, Carmel or Reed blame the military. They express pride in their service. “I wouldn’t trade it [military service] for anything in the world,” Reed said.

“The military’s job is to kill our enemies,” Gobin said. “I don’t think it’s their job to fix us. I think it’s the American people who should help us get back to who we were.”

Carmel’s wife, Catherine, who came from their home in Washington state to witness the trail’s-end celebration, said she could tell her husband had changed. Besides being a lot thinner, the 50-year-old Carmel looked younger every time she saw him during the hike, she said.

“He seemed so incredibly happy,” Catherine Carmel said. “He smiled for pictures. He didn’t look haunted.”

Reed said he wasn’t sure how much of his trail experience would return with him to his life in Minnesota, but he likes what he found in the woods.

“I put it this way: I went to the trail to find myself,” Reed said, “and I found someone better.”