The 34-year-old from Austin, Texas, said he felt duty-bound to return after losing his right foot to a land mine in Iraq.

"It sounds ridiculous, but you feel guilty that you're back home safe," he said. "Our country is engaged in a war. I felt it was my responsibility as a leader in the Army to continue."

Rozelle commanded a cavalry troop and conducted reconnaissance operations when he returned to Iraq, just as he had before the mine blast. Other amputees who have returned to combat, ranging from infantry grunts to special forces soldiers, have conducted door-to-door searches, convoy operations and other missions in the field.

"Guys won't go back if it means riding a desk," Rozelle said.

He said his emotions at the start of his second tour in Iraq, which lasted four months, were a lot like those during his first stint: "I was going back to war, so it was as heart-pounding as the first time."

Mark Heniser, who worked as a Navy therapist for 23 years before joining the amputee program at Fort Sam Houston in 2005, said both the military and the wounded benefit when amputees can be kept on active duty: The military retains the skills of experienced personnel, while the soldiers can continue with their careers.

Staff Sgt. Nathan Reed, who lost his right leg a year ago in a car bombing, is 2 1/2 years from retirement and has orders to head in July to Fort Knox, where he expects to be an instructor.

"My whole plan was to do 20 years," said the 37-year-old soldier from Shreveport, La. "I had no doubt that I would be able to go back on active duty."

Not everyone comes through treatment as rapidly or as well as Williamson, Reed and Rozelle. Some have more severe injuries or struggle harder with the losses, physically or emotionally. Soldiers who lose a limb early in their careers are more likely to want out. Those with long service are more motivated to stay, Heniser said.

Williamson did not want to return to combat, and it is not clear he could have met the physical qualifications anyway.

The military planned to discharge him on disability, but he appealed, hoping to become a drill instructor.

The Army ruled that would be too physically demanding for Williamson, a human resources officer before being sent to lead convoys in Iraq, but it agreed to let him return to active duty in some other capacity.

He is regaining his strength and balance at the new $50 million Center for the Intrepid, built to rehabilitate military amputees. A hurdler in high school, he ran the Army minimum of two miles for the first time in mid-May, managing a 10-minute-per-mile pace on his C-shaped prosthetic running leg decorated with blue flames.

He is working out five days a week — running, lifting weights and doing pool exercises — and just got his first ride on a wave machine used to improve balance.

"I could leave here today if they told me I had to," Williamson said.

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