The Granite Mountain Hotshots, an elite firefighting team in Prescott, Arizona, observed a moment of silence Wednesday to remember 19 of their teammates who died battling the Yarnell Hill fire on Sunday.

One of the fallen, 23-year-old Robert Caldwell, was born and raised in Richboro, Bucks County, before moving out West with his family.

His family first spoke with WHYY/NewsWorks content partner NBC10.

David Caldwell said his son was devoted to being a hot shot.

"He never missed a call, always on time. Moved up in the ranks," he said. "He was actually a crew boss on the squad that got wiped out." 

He says his son was self-sacrificing, and committed to helping people. 

He knew all there was to know about wildfires, right down to wind patterns and how different types of trees would burn.

He had also helped his cousin, 21-year-old Grant McKee, become a hot shot. McKee was also among the 19 killed battling the Yarnell fire on Sunday. 

Their deaths mark the largest loss of firefighters in a single disaster since 9/11. 

"And we're very, very very proud of him. And we just want people to know that there's other guys out there doing it right now," Caldwell said. "And they're putting their life on the line doing the same thing."

Caldwell says his son leaves behind a wife and a stepson.