BETHESDA, Md. — Almost every Thursday during the academic year, a bus carrying a dozen or so Naval Academy midshipmen leaves Annapolis for the 45-minute drive to Bethesda, where Navy doctors perform laser eye surgery on them, one after another, with assembly-line efficiency.

Nearly a third of every 1,000-member Naval Academy class now undergoes the procedure, part of a booming trend among military personnel with poor vision. Unlike in the civilian world, where eye surgery is still largely done for convenience or vanity, the procedure's popularity in the armed forces is transforming career choices and daily life in subtle but far-reaching ways.

Aging fighter pilots can now remain in the cockpit longer, reducing annual recruiting needs. And recruits whose bad vision once would have disqualified them from the special forces are now eligible, making the competition for these coveted slots even tougher.

But the surgery is also causing the military some unexpected difficulties. By shrinking the pool of people who used to be routinely available for jobs that do not require perfect eyesight, it has made it harder to fill some of those assignments with top-notch personnel, officers say.

When Ensign Michael Shaughnessy had the surgery in his junior year at the Naval Academy, his new 20-20 vision qualified him for flight school. And that is where he decided to go after graduating last month ranked in the top 10 percent of his class, rather than pursuing a career as a submarine officer.

"The cramped environment in submarines is something that turned me off," Shaughnessy, 22, said.

He is not alone. For generations, Academy graduates with high grades and bad eyes were funneled into the submarine service. But in the five years since the Naval Academy began offering free eye surgery to all midshipmen, it has missed its annual quota for supplying the Navy with submarine officers every year.

Officers involved say the failure to meet the quota is due to many factors, including the perception that submarines no longer play as vital a national security role as they once did. But the availability of eye surgery to any midshipman who wants it is also routinely cited. "Some of the guys with glasses who would have gone to submarines or become navigators are getting the chance to do something they'd rather do, and the communities that are losing the people are not as happy about it as the aviation community, which is gaining better candidates," said Cmdr. Joseph Pasternak, the ophthalmologist who oversees the program at the National Naval Medical Center in Bethesda.