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PORTLAND, Maine (NECN) -- There are more than 21 million veterans living in the United States.And for some of those servicemen and women, the biggest challenge wasn't serving their country--it was making the transition back to civilian life.

Retired Marine Sergeant Brendan O'Toole, of Alexandria, VA just completed a year long road trip to raise awareness about their plight. He ran 3,600 miles, from Oceanside, California to Portland, Maine, through 21 states.

"You start to get real tired out there. We had terrible weather, tornadoes, sandstorms, blizzards, dogs chasing us," said O'Toole. "It's been rough."

But the 26-year-old, who served in Afghanistan and Haiti, said his challenges on the road were nothing compared to those faced by many combat veterans when they return to civilian life.

"When I got out of Afghanistan, I had a buddy who struggled with PTSD and took his own life," recalled O'Toole. "And I ran into my own issues with the VA when I got out. I went out one night with my buddies and I started talking about these issues."

He says the highlight for him was standing atop the Freedom Tower holding the American flag.

He completed his mission on Veterans Day 2013 in Portland with a quick dip in the Atlantic Ocean.

Supporters, most of whom were veterans themselves, said they were grateful to O'Toole for drawing attention to the ongoing needs of servicemen.

"I think we're doing a better job than when I came back from Vietnam," said Marine Veteran Reynolds Young. "But there are an awful lot of kids out there who still need mental support."

To that end, The Run For Veterans raised funds for three charities that provide social, mental and physical support for vets and their families.

The $400,000 raised so far will be divided among the USO, Give An Hour, and Team Red, White and Blue."

Up next for the runner: "A long nap!!" O'Toole said laughing.

While his body is tired, he says his spirit has been rejuvenated by the support he's received along the way -- the same support he says all Veterans need when their tours end.

Two filmmakers accompanied O'Toole on the trip.

They're hoping to release a documentary about the "Run for Veterans" in 2014.

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