At the Air Force Academy, reports of sexual assault fell from 52 in 2011-2012 to 45 in 2012-2013. At the Military Academy, they fell from 15 to 10 during the same period.

Eleven of the reports among the three academies involved incidents alleged to have occurred before the victim entered their service. It was not clear how these reports were divided among the academies.

Advocates for victims say the relatively low rate of reporting, compared to the estimated number of incidents, shows a lack of faith in the military justice system.

"The victims do not have the confidence that the system will work for them," said Rep. Jackie Speier, the leading House critic of the military rules. Of the 29 cases in which an alleged victim agreed to cooperate with investigators, she said, "only one has gone to court-martial. That's 3 percent."

Speier, a California Democrat, has championed legislation to take the prosecution of sexual assault out of the chain of command. Sen. Kirsten Gillibrand, a New York Democrat, has filed similar legislation in the Senate.

Military officials say they encourage all victims to report assaults, in order to get treatment and to hold perpetrators accountable.

Baltimore Sun reporter Pamela Wood contributed to this article.

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Sexual assault at the service academies

Reports by academic year

Air Force AcademyMilitary AcademyNaval AcademyTotal

2009-1020101141

2010-1133102265

2011-1252151380

2012-1345101570

Source: Department of Defense's Sexual Assault Prevention and Response Office