Of all the challenges facing troops these days, erectile dysfunction may seem an odd one for the military to study.

Turns out the Armed Forces Health Surveillance Center regularly scours medical records across all branches to track trends and troubles that don't just threaten health and mission, but also take a toll on quality of life.

ED, as erectile dysfunction is commonly called, was a topic in the latest Medical Surveillance Monthly Report, a regular publication of the Maryland-based center - the military's version of the Centers for Disease Control and Prevention.

Blessed with a captive study group - 1.2 million service members whose medical records are electronic and accessible - the center's researchers were able to review 10 years worth of records to glean the diagnostic codes associated with ED.

The bottom line: 100,248 new cases were diagnosed from Jan. 1, 2004, through Dec. 31, 2013, a rate that, at least in raw numbers, is close to civilian figures.

Cause is the biggest difference.

In the civilian world, the roots of ED are often physical or medication based. In the military, they tilt toward the psychological.

Both sectors report an increase in ED, defined as the persistent inability to achieve and sustain an erection adequate for sexual intercourse.

Over the study period, the annual number of servicemen seeking treatment for ED doubled.

Outside the military - where researchers can only sample, survey and estimate - prescriptions offer the best gauge. Doctors wrote 8 million Viagra prescriptions in 2012.

But the "little blue pill" itself could be pushing up the case numbers. Introduced in 1998, Viagra - and similar drugs - that followed inspired untold men who might have otherwise remained silent to go for help. What appears to be an increase could simply be more men willing to talk about it.

Among the study's findings:

* Less than 1 percent of active-duty servicemen age 40 and under were diagnosed with ED.

* Nearly half of all cases were attributed to psychological issues (post-traumatic stress disorder, stress, depression).

* There was a greater increase in cases attributed to psychological factors than physical ones (obesity, smoking, cardiovascular disease, medication use).

* Black, non-Hispanic servicemen had higher rates (due to ethnic risk factors such as hypertension and diabetes).

* Separated, divorced or widowed servicemen had an almost four times higher rate than those who had never married.

* Rates were lowest among servicemen with an education level of high school or less.

* Rates were highest among servicemen who had never deployed, a skewing that researchers attribute to the fact that only physically healthy troops are allowed to deploy.

More cases of ED are bound to surface, if the makers of Viagra have their way. Faced with a patent that expires in three years, Pfizer is stepping up its advertising. Its latest commercial is its first to feature only a woman. In a sexy British accent, she encourages men to try the drug.

Researchers at the surveillance center say their studies help shape Department of Defense policies. One change that's already occurred: After a six-year hiatus from military pharmacies, Viagra returned to the shelves in 2012.