Nearly a decade after being honorably discharged from the U.S. Marine Corps, John Gerula is still struggling to fit back into his hometown of Windber, Pennsylvania.

The now 33-year-old Iraq War veteran signed up for the Marines at the age of 18 -- two weeks after working as a first responder during the September 11 attacks. Gerula's first disaster call as a junior firefighter was to the crash of United Airlines Flight 93 in Shanksville, Pennsylvania.

John Gerula, 33, served in the U.S. Marine Corps for six years. CBS News

"I was one of the first responders there. We were the first vehicle on the scene," Gerula told CBS News. "That actually pushed me to join the military. I graduated high school early to join the Marine Corps."

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During his six years in the Marines, Gerula spent one year deployed in Iraq, served as part of a military intelligence unit and fought in "Operation Phantom Fury" -- the Second Battle of Fallujah, where U.S. troops fought against al Qaeda militants.

He survived numerous IED explosions.

"There were a lot of long, hot days in the sun and a lot of time off the Forward Operating Base," Gerula recalled.

When Gerula returned home in May 2007, he didn't think things would simply "go back to normal" -- but he never expected the transition to be as hard as it was.

He suffered from a traumatic brain injury and post-traumatic stress disorder (PTSD), which has caused added anxiety and stress for the veteran.

"It's tough trying to fit back into a society where veterans are having a hard time getting back in," Gerula said. "It's easy to put the uniform on, but it's very hard to get back in society when you have been doing that for so long."

To help work through his challenges, Gerula receives weekly counseling at a nearby VA facility.

"It's been hard. Coming back ... there's not much support when it comes to veterans," Gerula said. "It was tough in the beginning, but there are some groups out there now that are starting to help veterans."

One of those groups, Gerula says, is American Humane.

It's through the non-profit's new Shelter to Service program, which rescues homeless pets from shelters across the country and trains them to become service dogs for veterans, that Gerula met his new best friend: Oliver.

John Gerula, 33, and his new PTSD service dog, Oliver, meet for the first time. American Humane

The one-and-a-half-year-old terrier mix was abandoned by his owner and rescued from a shelter in Colorado. After three months of training, the dog was finally able to meet his new owner for the first time last week.

"It was an emotional experience. Me and him clicked right away," Gerula said. "He started giving me hugs. We were a match the first minute I touched his leash."

On Friday, Gerula attended a day-long training with Oliver, where he practiced basic commands with the dog.

The dog is trained to keep spaces between Gerula and others, sense when his owner gets stressed and even retrieve any medication he may need.

"When he puts that vest on, he's all business," Gerula said. "He's hyper-vigilant. He looks around. He stays on my left side and he will not move unless I tell him."

John Gerula and his new PTSD service dog completed a day-long training on Friday, July 14. American Humane

Amy McCullough, Ph.D., the national director of military of affairs at American Humane, recalls the day she recruited Oliver for the Shelter to Service program.

"He was standing there in his kennel, looking beautiful. He had been there for over two months with no one taking a look at him," McCullough told CBS News. "I brought him out. I met him. He was sweet, sensitive, so attuned to humans that he was the best candidate there."

It's not the breed of the dog that matters -- it's the temperament, McCullough explained.

And Oliver certainly has the right temperament for the job.

"He's very affectionate. Very loving. He loves to have attention. The attention has to be on him, and that's good, that keeps my attention on him," Gerula said. He described it as like having two different dogs: "Oliver the working dog and Oliver the play dog."

On Monday, Gerula took Oliver home to Windber, Pennsylvania, where he'll spend his days running around a one-acre yard, standing by Gerula's side as he works in his wood shop and volunteers at the local fire department.

John Gerula, 33, pets his new PTSD service dog, Oliver, who will help provide support for the Marine Corps. veteran. CBS News

"He'll go everywhere with me. He's very welcome at the fire department. They can't wait to meet him. They say he's the firehouse mascot," Gerula joked.

So far, three veterans, including Gerula, have been placed with service dogs through American Humane. Next year, McCullough hopes to increase that number fourfold.

"Every day 20 veterans take their own lives and over half a million shelter dogs are euthanized every year, so as an organization who has worked to help both these groups for over a century we're compelled to really address this challenge," McCullough said.