Washington (CNN) -- Sexual assaults at the U.S. military's three service academies increased drastically in the 2009-2010 academic year after four years of declines, a new report shows.

The academies reported 41 sexual assaults involving cadets or midshipmen compared with 25 the prior academic year, a 64% jump. But the report warns the problem may be 10 times greater than the statistics show.

A Department of Defense statement accompanying the report said the increase could mean more reporting, not more attacks.

"This may not indicate an increase in instances of sexual assault occurring, as it could also be a result of training and education and victims' confidence in the department's ability to respond," the news release said.

Anuradha Bhagwati, a former Marine Corps captain and executive director of Service Women's Action Network, called the Defense Department statement a ""pretty pathetic explanation." The network is a national human rights organization with a goal of allowing women to serve in uniform without threat of harassment, discrimination, intimidation or assault.

This week Service Women's Action Network and the American Civil Liberties Union sued the Pentagon and the Department of Veterans Affairs, seeking records on sexual assault in the military.

Bhagwati said reporting of sex assaults by academy students is rare. The Defense Department's report to Congress, which includes a survey of academy midshipmen and cadets, confirms that.

"These survey results suggest that the 41 reports of sexual assault at the (military service academies) accounted for fewer than 10% of the incidents of unwanted sexual contact that may have actually occurred," the report says; "12.9 percent of women and 1.9 percent of men survey at all three service academies indicated experiencing unwanted sexual contact."

The 41 sexual assaults referred to are not necessarily rape. The Defense Department has a wide definition of sexual assault.

"The term 'sexual violence,' herein referred to as 'sexual assault,' is defined as intentional sexual contact, characterized by use of force, threats, intimidation, abuse of authority, or when the victim does not or cannot consent," the report said.

"The reason that so many women and men do not report their sexual assaults," Bhagwati said, "is because there is a culture of intimidation. Not just at the military academies, but also ... in the armed services themselves."

She gave as an example a woman in the military who was being choked by a male service member trying to sexually assault her. She fought back and was charged with striking a fellow service member. The man who was choking her was not charged.

Greg Jacob, policy director for Service Women's Action Network, said the Defense Department has "an abysmal record of actually prosecuting sexual predators."

He gave an example from the one cadet at the Army's U.S. Military Academy at West Point who was convicted last May of raping a fellow cadet. The cadet, Kyle Newman, was sentenced to 3 1/2 years in prison. In New York state, first-degree rape is a class B felony, punishable by 12 1/2 to 25 years in prison.

All three of the academies claim things are improving.

"Over the course of the academic program year 2009-2010, the United States Military Academy made steady progress on the prevention of sexual harassment and violence," reads a memo from the superintendent of West Point.

"The United States Naval Academy continued to demonstrate its clear commitment to both the spirit and intent of Department of Defense and Department of the Navy Sexual Assault Prevention and Response Programs," reads the Naval Academy's part of the report.

And the Air Force Academy "continues to provide a very robust education and training program, to include seminars, guest speakers and targeted year-group focused training," according the Air Force portion of the report.

"These programs extend well beyond activities that heighten awareness of the problem," Kaye Whitley, director of the Sexual Assault Prevention and Response Office, said in the press release accompanying the report. "Not only do the academies have a well-organized response structure, they also incorporate sexual harassment and sexual assault prevention objectives into leadership and academic curricula."