When Tom McCollum transitioned from the 82nd Airborne to Special Forces, he knew the training would be tough.

The Special Forces Qualification Course, or Q Course, can take up to two years to complete, depending on a soldier's area of expertise. As a former company commander with ample leadership experience, McCollum was ready for the challenge. Still, he found himself struggling to adapt to a new role.

"All of a sudden, I found myself in SERE school, where I was the senior ranking officer, but no matter what I said, no matter what I did, was wrong," said McCollum.

SERE school, focusing on survival, evasion, resistance and escape, teaches soldiers what to expect if they become prisoners of war. Students must try to keep their wits during grueling mock interrogations designed to test their resolve.

"I had gone from a position where people looked to me for guidance, where I was taking care of them, to people looking at me hoping I wouldn't say anything, said McCollum. "It was a complete shock and reversal from everything I was used to. I remember I had a hard time dealing with that."

The experience forced him to see himself in a new light. McCollum said it was the biggest mental challenge he faced in his Army career.

"I think that was a good thing. At the time I wouldn't have said that was a good thing, but it's one of those lessons that you learn that dawns on you years later."