Dr. John Caulfield thought it had to be a mistake when the Army asked him to return to active duty. After all, he's 70 years old and had already retired -- twice. He left the Army in 1980 and private practice two years ago.

"My first reaction was disbelief," Caulfield said. "It never occurred to me that they would call a 70-year-old."

In fact, he was so sure it was an error, at first he ignored the postcards and telephone messages asking if he would be willing to volunteer for active duty to "backfill" somewhere on the east coast, Europe or Hawaii. That would be OK, he thought. It would release active duty oral surgeons from those areas to go to combat zones in Iraq or Afghanistan.

But then the orders came for him to go to Afghanistan.

Today, Caulfield, a colonel, is an example of how the continuing demands of keeping ground troops in Afghanistan and Iraq are straining the military, and forcing the various branches to go to extraordinary measures to keep the ranks filled. He's attending to patients -- U.S. troops, Afghan soldiers and civilians \ufffd at the Army's 325th Field Hospital in Bagram, Afghanistan.

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"The rules say it's at 60 years of age when people retire," said Dov Schwartz, an Army spokesman. But the Army will issue waivers allowing people who are older to serve if they have needed skills. Returning, though, is "totally voluntary," Schwartz said.

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When the call-up came, he had no qualms about serving. He said that because the wars in Afghanistan and in Iraq were within such a close time, the military is exhausting some specialties. They have rotated some reservists in and out.

"Because there is no draft they are using and maybe overusing the National Guard and Reserve," he said. "There is no obligatory method."

Caulfield said he is glad to be able to help.