David Letterman spent part of Friday joking about racing.

He was totally serious when the discussion turned to the mission of raising money and awareness about a medical device called exoskeleton, which helps paralyzed veterans regain some mobility.

“Five years ago, I didn’t realize veterans had problems returning. It’s not like World War II and it deserves all the attention it can garner,” Letterman said. “I’ve seen them work, I’ve seen them take a man out of a wheelchair and walk.”

Letterman was referring to a scene at Sonoma last season when injured U.S. Army Sgt. Dan Rose walked across a stage to meet Letterman, a moment team co-owner Bobby Rahal said brought many to tears.

Rose is expected to attend his first Indianapolis 500 on May 28, where he’s hoping to see Graham Rahal reach victory lane.

United Rentals, one of the team’s sponsors, has agreed to donate $50 for every lap Rahal completes this season to the SoliderStrong charity through its Turns for Troops program. This month’s donation will be bumped to $100 for Saturday’s IndyCar Grand Prix and the 500.  Shirts are also being sold at the track shops for $35, and all proceeds will help purchase equipment that costs $200,000.

For most of the 20-minute news conference at Indianapolis Motor Speedway, Letterman spoke poignantly about helping wounded veterans.

He decried the need for war and the injuries that occur from it. He urged wealthy people, such as Elon Musk, to donate, too. And Letterman promised to what he could to pitch in.

“Look, I’m at the tail end of this and I’m just happy to be included,” he said. “If there’s anything I can do to push it along great.”