Thomas J. Brennan was a sergeant in the United States Marine Corps, as well as an infantryman in Iraq and Afghanistan with the First Battalion, Eighth Marines. He had every “basic infantry thing” memorized—that is, until he got blown up.

Stationed at Outpost Kunjak in the Helmand Provence of Afghanistan, Brennan and his unit, the Third Platoon, Fourth Squad, were on a mission to push on 4,000 meters to a target building, aiming to ambush the Taliban. A few hundred meters into their mission, the platoon was met with enemy fire, Brennan recounts in a video created by Reuters.

Brennan, a member of the Military Order of the Purple Heart, shared his story of injury, trauma and recovery with an approximate 50-person audience Thursday night, describing his journey from a marine on the frontlines to an esteemed investigative journalist.

The enemy had rockets and machine guns, “and that’s when I got blown up,” he told audience members.

On his short but full timeline, Brennan was medically retired from the Marine Corps in 2012, graduated from the University of Massachusetts in 2014 with his bachelor’s in journalism and graduated from Columbia in 2015 with his masters in investigative journalism. Along the way, he founded The War Horse, a publication that reports on war, trauma and the effects of post-9/11 conflict.

“He has put a spotlight on what’s wrong with the system,” Catherine Epstein, dean of the faculty at Amherst College and host of the event, said about Brennan.

She noted that he has broken a lot of big stories, including one that drew attention to the U.S. Department of Defense’s investigation into “hundreds of Marines who used social media to solicit and share hundreds—possibly thousands—of naked photographs of female service members and veterans.”

“There’s a lot to his story. I think one of the things they [students] can really takeaway is what is the military doing about mental health issues,” Epstein said. “I think that’s what’s remarkable about what Thomas is doing is really making clear the challenges that veterans face in terms of dealing with mental health and those kinds of issues.”

Kevin Cullen, an author, Pulitzer Prize-winning journalist and veteran reporter for The Boston Globe, lead the personal and, at times, emotional discussion. Cullen is a fellow UMass journalism alumnus and now works as a columnist at the Globe, as well as an editorial advisor at The War Horse.

When asked by Cullen about his injury, Brennan described how he was knocked unconscious by a rocket propelled grenade that an Afghanistan National Police officer shot at him. The warhead hit the telephone pole near him, from which he sustained a third-grade concussion.

The next 15 days were spent in a field hospital. Even after the medical doctors cleared him to return to the battlefield, Brennan still had trouble remembering things, including his 9-line MEDEVAC, a procedure used to call in a combat injury that all U.S. soldiers learn early on in basic training.

After the accident, Brennan said he started getting “crazy” migraines. To combat them, he would down six to eight Starbucks VIA Instant packets a day. Having been okayed by the doctors to serve again, he didn’t feel like he could ask for help. He struggled on the front, but it was back at home where he struggled even more.

“I knew I wasn’t broken but that I was cracking and falling apart,” Brennan said. “I had to try and put on a front.”

Although he recounted this period of emotional struggle matter-of-factly, Brennan said he felt isolated after returning home. One night at a bar, Brennan watched an amputee, a fellow veteran, walk in. At that point, Brennan “lost it,” begging his wife to help him find a gun, so he could shoot himself.

“It was a very demoralizing experience,” Brennan said.

It was at this point that Brennan’s wife told him he needed help; in responding to Cullen’s question of how he made the “transition from warrior to journalist,” Brennan described how a main part of his recovery was through writing.

Brennan talked about how early on in his recovery, his social worker, Frank, got frustrated that Brennan didn’t know what to talk about. So, Frank gave him a notebook and told Brennan to keep it on him and write all his thoughts down.

“I haven’t put it down since,” Brennan said, adding that writing gave him a purpose.

“It’s really easy to feel like you don’t mean anything when you’re on the side of a mountain in Afghanistan,” he said.

One of Brennan’s first positive experiences with a journalist was during his deployment. At Outpost Kunjak, Brennan met a “gaunt” man from Reuters, a photojournalist named Finbarr O’Reilly, who spent a month with Brennan’s battalion. At the time, Brennan didn’t think war and journalism mixed; he thought of ways he could get rid of O’Reilly, including shooting him in the foot.

However, Brennan said that O’Reilly gained his trust after the two were under fire together. On the day of Brennan’s injury, O’Reilly witnessed and took photographs of the series of events. Now, the photographs serve as some of Brennan’s most prized possessions. He noted that they were helpful in explaining his accident to his family.

Five years and 20 New York Times articles later, Brennan has now co-authored a book with O’Reilly, titled “Shooting Ghosts.” The book is a joint memoir of the photojournalist and Marine-turned-journalist, covering “their story about the unpredictability of war and its aftermath…and explores the things they’ve seen and done, the ways they have been affected, and how they have navigated the psychological aftershocks of war,” according to O’Reilly’s website.

Writing was therapeutic for Brennan. In describing his book, he said, “It was me taking this jumbled mix of letters and notes and feelings and putting it into one organized place.”

“Shooting Ghosts is my attempt to find closure from my own service, my own injury,” Brennan added.

Paul Keating, a Vietnam veteran and 1976 UMass alumnus, told Brennan during the question-and-answer portion of the event that Brennan’s generation of young veterans inspires him.

“I’m 70 years old…I still haven’t found it,” Keating said about still struggling to find closure to his military service and subsequent trauma.

“You guys give me hope,” he said.

Jackson Cote can be reached at jacksonkcote@gmail.com and followed on Twitter @jackson_k_cote.