Brennan Mullaney, a captain in the Army Reserve, said the bombs in Boston were more shocking than those he experienced in Iraq. (Michele McDonald/FOR THE WASHINGTON POST)

When the bombs went off near the finish line of the Boston Marathon on Monday, Brennan Mullaney and Eusebio Collazo were together on the course at mile 25.

Mullaney, now a captain in the Army Reserve, served 15 months during the “surge” in Iraq. Collazo of Humble, Tex., a former Marine corporal, was wounded in Iraq’s Anbar province by mortar shrapnel and suffers from post-traumatic stress disorder.

They were approaching Boylston Street as members of a national nonprofit group that promotes healing among veterans, Team Red, White & Blue. And then suddenly the tables turned, and they found themselves helping to heal and comfort a city that had never experienced a roadside bomb.

“The real crazy symbolism here is that this was essentially an IED, an improvised explosive device,” said Army Maj. Mike Erwin, who founded the team in 2010 to help veterans heal and re-integrate into their communities through running and other physical activities. “What runners and the community experienced in Boston is the exact same thing that hundreds of thousands of service members have experienced since 2002, when they started using IEDs in Iraq and Afghanistan.”

As smoke wafted across Boylston Street and maimed marathon spectators lay across a bloody sidewalk, one veteran, an Army colonel and runner, shifted into combat mode as he crossed the finish line. He turned back into the chaos, peeled off his Team Red, White & Blue T-shirt and tied it as a tourniquet on the limb of a bombing victim.

A combat veteran who served in Iraq and was awarded a Purple Heart, the colonel later refused to allow a team spokesman to release his name after snippets of his actions were caught on video.

Turning T-shirts into tourniquets is not something most spectators along the marathon course would have had much experience with. “When we’re deployed, we all carry tourniquets — nice ones,” said Mullaney, 30, of Cumberland, Md., now a graduate student at Tufts University. “When you see missing limbs, the first thing all of us know is to tie a tourniquet.”

There are more than 485,000 Iraq and Afghanistan veterans who are thought to be suffering from “invisible wounds” — PTSD, traumatic brain injury, and other psychological and emotional maladies, said Larry Olson, a spokesman for Team Red, White & Blue.

The physical and emotional benefits of exercise have been exhaustively studied and documented. Exercising in groups brings veterans isolated by their combat experience back into their communities, Erwin said.

More than 10,000 veterans and supporters in 36 states have signed up to be part of the organization, running, trail running, training for triathlons and doing yoga.

“Exercise is therapeutic. It allows you to think and process. And it’s a hell of a lot better than sitting across from a shrink,” Erwin said. “Running is such a more natural and organic way for veterans to share things on their minds.”

So the Boston Marathon became a maximum therapy session Monday for 17 Team Red, White & Blue participants, running the rolling hills from Hopkinton, through Natick, Newton and Wellesley, and then into Boston until, by the time Mullaney and Collazo approached, it became a war zone.

“Some lady on the street said there’s been a bomb at the finish line,” Mullaney said. “We looked at each other and thought, that’s a terrible joke to play on someone. We kept running, but then I started to pick up on clues that maybe something really did happen.”

Sirens blared from all directions and, up ahead on Commonwealth Avenue, race officials had shut down the course. The vets went from people running to heal, to people counseling their fellow runners. “It is a lot like the tables have turned,” Mullaney said. “There’s a number of civilians who’ve been put in a war zone, and there’s a number of veterans who’ve experienced that and can say, ‘We’re here.’ ”

In the chaotic aftermath of the bombing, Team Red, White & Blue team members from across the country began posting on Facebook a photo and a short video of the shirtless colonel aiding a victim on the sidewalk, her face showing agony.

Wrote one: “A picture of Team RWB in action today in Boston, taking his shirt off to provide first aid to the injured. We are posting these pictures and videos as they come in because we feel it is important to remind one another of the positive things happening amid the chaos and the evil.”

“Taking the eagle shirt off his back,” Erwin commented. “Team RWB providing first aid to the injured. Sheep dogs.”

“Sheep dogs,” added another poster. “We are our brothers’ keeper.”

Mullaney said he found the bombs on Boylston Street far more shocking and traumatic than those he and other veterans experienced in Iraq. “When it happens in your back yard, your home, your community, it’s exponentially more painful,” he said. “When it happens here, it’s innocent people — that’s the nature of terrorism.”

The crowds dissipated and police cordoned off a dozen blocks around the finish line, turning the Back Bay into the largest crime scene in Boston history. Team Red, White & Blue members from the Boston area, led by Mullaney, gathered Tuesday at dusk along the Charles River at Massachusetts Avenue, several blocks from the marathon course, for what they called a “response run.” Forty other team chapters across the country did the same.

“This is our organization’s response to the attacks,” Erwin said. “We’re responding to the negative energy, the pain and the evil with hope and strength and optimism.”