CHICAGO — Former Army Sgt. Kevin Cajas served two tours in Iraq, where half a dozen of his friends died in combat and many others were wounded. Yet it never crossed his mind that he was risking his life for a country that had yet to embrace him as one of its own.

"What mattered was that I was a soldier," Cajas, 27, said, "and we had a mission."

On May 23, Cajas, a native of Guatemala, was sworn in as a U.S. citizen alongside 29 other immigrant service members, known as "green card warriors," during a naturalization ceremony at Pritzker Military Library.

"From this day forward you defend our Constitution not just as soldiers, but as citizens," keynote speaker Air Force Brig. Gen. Darren McDew said.

"From the revolution onward, our military has been comprised of men and women, many of whom were not born here, who nonetheless felt allegiance to the values of the American spirit."

The new citizens came from 14 countries and represented all five branches of the military. They wore Navy dress whites and Army camouflage fatigues. Some had enlisted to earn money for college or to secure a stable future. Others were compelled by patriotism.

For Cajas, who was honorably discharged from the Army in 2006 after enlisting in the wake of the Sept. 11, 2001, terrorist attacks, the crisp, new naturalization certificate was the ticket to a political voice.

"That piece of paper is going to allow me to vote," he said. "That's probably the most exciting thing."

Sgt. Isaura Guerrero-Perez, 25, wiped tears from her eyes after the ceremony. A Mexican immigrant, she grew up in Carpentersville and enlisted in the Army Reserve to help pay for college.

"I'm really proud of being here, of being a citizen, of wearing the uniform," said Guerrero-Perez, who is working on a master's degree in accounting at Northern Illinois University.

Military citizenship ceremonies have taken place around the country and the world, with more than 39,000 immigrant service members naturalized since 2001. The government also has naturalized 115 immigrants who died in combat.

Immigrants must be permanent legal residents, or green card holders, to join the military. More than 65,000 foreign-born service members are in the armed forces. They represent about 5 percent of all active duty personnel, according to a report released this month by the Migration Policy Institute.

A 2002 executive order gave immigrants in the military a fast track to citizenship, allowing those who served after Sept. 11 to apply immediately, rather than waiting three years. They must still fulfill requirements such as background checks and fingerprinting, but military petitions are flagged and moved to the front of the line at a special processing center.

Military personnel are assigned to guide immigrants through the often unwieldy application process. Sgt. Daniel Perez, one of the organizers of the May 23 ceremony, helped hundreds of soldiers in Iraq apply for their citizenship.

"They have grown up seeing their parents work hard to make a better life," said Perez, 31, of Blue Island. "One way to give back to the country that has accepted your family is to serve in the military."