"It's time for me to give something back to this great country," Pena said. "Baseball is great. I love baseball. But what those guys do for us and what this great country did for me is something where I feel I have to give something back."
Pena said he first considered joining the Army Reserves a few years ago and talked about the possibility with former Reds teammate Jay Bruce. The calling continued to eat at him, and that led Pena to reach out to an Army recruiter to talk about his options. The Cardinals did not know about Pena's decision until the 34-year-old catcher posted the news on Twitter.
General manager John Mozeliak said he intends to meet with Pena this week to discuss the issue further and get more clarification on what activities Pena intends to participate in. Pena is under contract through the 2017 season.
"We have not really had to deal with military issues with current players," Mozeliak said. "Most of the rules in Major League Baseball were written back for World War II and subsequently the Korean War and Vietnam. It's not something I've had to actively follow up on.
"Look, it's a very patriotic move after July 4. Nothing surprises me with Mr. Pena now."
The Cardinals have dealt with a different sort of military service requirement before, as injured reliever Mitch Harris served nearly five years as a US Naval Lieutenant after being drafted by St. Louis. He is still a member of the Reserves, but fulfills those obligations during the offseason.
Pena's patriotism is tied directly to his past. He defected from Cuba when he was 16 years old and signed with the Braves in 2000. He became a US citizen eight years later.
"Just the fact that I was able to find something that I didn't know existed," Pena said. "I was able to find freedom. I was able to find hope. America gave me all that. Obviously, my wife and my beautiful kids, I met her here and they were born here. It's something I really appreciate."
Pena noted that he would volunteer for active duty - even if that meant giving up his baseball career - if the Army asked him to. That's an unlikely request, however, since Pena won't officially be enlisted in the Reserves.
Part of Pena's interest in reaching out to the Army Reserves now was to also create a path for involvement once he retires. Pena would not commit to extending his playing career beyond the end of his current contract.
"I'm not going to say it's my last baseball contract, but I'm not 25 anymore," said Pena, who, after a stint on the disabled list, made his second start of the season on Tuesday. "I get that. You have to follow your heart and follow exactly how you feel. This is how I feel."