Women serving in the U.S. Marine Corps and the Navy are at a higher risk of being sexually assaulted, according to a new Pentagon report.

Indeed, female Marines are at the highest risk -- almost three times as likely as their Air Force counterparts to be victims of sex crimes, according to the study, which was released Thursday and included results from the largest-ever survey of sexual assault and harassment in the military.

The presidentially mandated report estimated that 7.9 percent of female Marines and 6.5 percent of female sailors were victims of sexual assault in fiscal 2014, while 4.7 percent of female soldiers and 2.9 percent of female airmen were similarly abused.

"A significantly higher proportion of women in the Marines and Navy are estimated to have experienced sexual assault in the past year than women in other services," it states.

Navy Rear Adm. Richard Snyder acknowledged "the differences in the prevalence rates between the services," but pointed to other survey data that show sex assaults in the service decreasing over the past two years even as more victims come forward to report such crimes.

"We're in no way declaring a victory or declaring success in our battle to prevent sexual assault," he said during a conference call with reporters. "We're declaring progress."

Overall, almost 5 percent of women and 1 percent of men in the U.S. military -- roughly 20,000 troops among an active-duty force of 1.3 million -- were estimated to be victims of "unwanted sexual contact," a broad definition that includes such offenses as groping or rape, according to the document.

The figures are based on a survey conducted from Aug. 7 to Sept. 24 by Rand Corp., a nonprofit research group based in Santa Monica, California, of more than 145,000 active-duty service members, with a response rate of more than 30 percent.

"The estimated rate of sexual assault varied dramatically by gender: fewer than 1 in 100 men but approximately 1 in 20 women," it states.

And while there were smaller differences by branch of service, both the Marine Corps and the Navy also had the highest incidence rates by type of sexual offense.

For example, the Marine Corps had the highest level of so-called penetrative sexual assault, or rape, with an estimated 4.3 percent of women and 0.63 percent of men experiencing such crimes, according to the report.

Meanwhile, the Navy had the highest level of so-called non-penetrative sexual assault, which includes groping or touching genital areas, with an estimated 3.6 percent of women and 1 percent of men experiencing such crimes, according to the study.

"There is ... evidence of significantly higher estimated percentage of female Marines who experienced a penetrative sexual assault and male sailors who experienced a non-penetrative sexual assault, relative to members of the same genders in other services," it states.

Snyder said another military survey shows the rate of unwanted sexual contact among women in the service decreased from 7.2 percent in fiscal 2012 to 5.1 percent in fiscal 2014, and among men from 2.7 percent to 1.1 percent over the same period. What's more, he said, the reporting of such crimes increased from one in 17 victims in 2012 to one in five victims in 2014.

"We're going to work to continually and aggressively go after the incidents of sex assault and increase the willingness to report," he said. "We'll work with the other services and organizations to [identify] best practices and look at ours as well as to make sure we're doing the best we can in prevention and response."

The study came a day after news outlets reported that the sea service was investigating a 24-year-old male enlisted sailor who secretly videotaped some of the first female submariners while they were showering aboard the ballistic missile submarine USS Wyoming.

The release of the document coinciding with the latest in a string of high-profile involving sexual assault or harassment in the services is likely to add fuel to the debate over how to reform the military legal system to better prevent and prosecute such offenses.

The military's top brass has fiercely resisted calls from lawmakers, led by Sen. Kirsten Gillibrand, a Democrat from New York, to give uniformed prosecutors rather than commanders the authority to decide which cases should go to court-martial.

The estimate that almost two-thirds of victims who reported the crime to their chain of command were retaliated against "should be a screaming red flag," she said in a statement in response to the report’s findings. "Last December the President said he would give the military and previous reforms a year to work and it is clear they have failed in their mission."

-- Brendan McGarry can be reached at brendan.mcgarry@monster.com