Their stories started like many; they were somewhere else when the attack happened.
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"At the particular moment, I was working at the Bryn Mawr Post Office," said chaplain Shakur Abdul-Ali.
When the towers fell, however, all four of them felt the need to go.
"We served together, sometimes two by two," said chaplain Perry Messick.
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Like most Americans, their lives were forever changed.
"We come to remember those who gave their lives," said senior chaplain Gary Holden, who runs the Four Chaplains Memorial Foundation.
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He helped put 3,000 flags in the ground in front of the chapel to honor lives lost 20 years ago.
"No, I can't believe it. It's like yesterday. It really is like yesterday," Holden said.
He spent months on Ground Zero helping whoever he could.
"A lot of times, you would think it's all a matter of what you say. No, it's not. It's all a matter of your heart, and it's a matter of you listening to them," said chaplain Don Harrington.
Abdul-Ali, a Muslim chaplain, recalled the events 20 years ago and says he experienced prejudice on Ground Zero but still kept faith in his calling to help.
"When you have a calling, God is your protector. So I wasn't worried too much. I mean, I heard things. I saw things. There was writing on the wall of different things, but my calling was a higher calling," he said.
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Messick says it was a calling for him too.
"I appreciate the people that came out to this and that they are remembering. It means a lot that they're remembering," said Messick.
All four of the chaplains agree that reliving the events of September 11 and the months that followed can be painful, but they've also found hope in their memories and the people they've helped.
"We'll never forget the impact it made on our lives as we were there trying to help others. It really changed our lives as chaplains," said Holden.