WASHINGTON — Greg Barker’s documentary “Legion of Brothers,” which debuts on CNN on Sunday night, tells the story of the special forces units that were instrumental in rooting the Taliban out of Afghanistan in the initial months following 9/11.

But the project is unique in that it captures the thoughts and emotions of the special forces units more than 15 years later, including their candid observations about their discomfort as they waged what has been called a “secret war.”

“There’s the Hollywood version of ‘gung ho’ SEALs. It is really not that way,” Barker told Variety‘s Ted Johnson on SiriusXM. “The people who are recruited to these elite units are incredibly intelligent, thoughtful, sophisticated people. Elite soldiers. But they really do think and reflect on what they are doing. And the killing, and what it means for themselves and our country. They would like us all to reflect on what we ask them to do when they do these jobs.”

He adds, “The horror of war stays with them for the rest of their lives. They just never really get that out of their head.”

President Donald Trump has announced more troop deployments to Afghanistan, where the U.S. involvement is nearing 16 years, the longest in history.

Barker said that in his conversations with the veterans of the initial mission in the country, they would like to see a strategy where soldiers on the ground are given “more flexibility [to do] what they see fit in that the moment.”

“Just having more troops there is not always the answer,” he said. “If we have troops not trained in local culture, and not trained to work through our allies on the ground … then you are in a position where you have a large footprint trying to impose the will, and that invariably leads sort to some kind of reaction, which is not always a good one.”

Listen below:

The documentary airs at 9 p.m. ET on CNN.