The anonymous online questionnaire by the Marine Corps surveyed 53,000 troops last summer, with the results provided to Defense Secretary Leon Panetta before he opened thousands of combat positions to women last week.

The Marine Corps released the results to The Associated Press on Friday.

Among the other top concerns listed by male Marines were possible fraternization and preferential treatment of some Marines.

Respondents also worried that women would be limited because of pregnancy or personal issues that could affect a unit before it’s sent to the battlefield.

Military experts said the results were not surprising because the Marines have the highest percentage of males among the branches of the armed forces.

Former Marine infantry officer Greg Jacob of the Service Women’s Action Network said the Pentagon’s estimate that 86 percent of assault victims opt against filing complaints “suggests that there’s hardly an overabundance of reports, false or otherwise.”

Some, however, said the survey shows the need for sensitivity training and guidance from leadership so the change goes smoothly, as occurred when the military ended its policy that barred openly gay troops.

“I think there is this sense among what I would imagine is a very small minority of Marines that this male bastion is under siege and this is one more example of political correctness,” said David J. R. Frakt, a military law expert and lieutenant colonel in the Air Force reserves.

Just as the Marine Corps adjusted to the end of “don’t ask, don’t tell,” despite being the most resistant among the military branches, troops will likely fall in line again with this latest historical milestone, said Frakt, a visiting professor at the University of Pittsburgh.

Marine Corps officials did not respond to a request for comment on the survey results.

About 17 percent of male Marine respondents and 4 percent of female respondents who planned to stay in the service or were undecided said they would likely leave if women move into combat positions. That number jumped to 22 percent for male Marines and 17 percent for female Marines if women are assigned involuntarily to those jobs, according to the survey.

Both sexes mentioned intimate relationships between Marines and feeling obligated to protect female Marines among their top five concerns about the change.

Female Marines also said they worried about being targeted by enemies as POWs, the risk of sexual harassment or assault, and hygiene facilities, according to the survey, which did not give specifics.

The women surveyed also expressed concern about acceptance and physical abilities if given a ground combat job.

About 31 percent of female respondents — or 1,558 women Marines — say they would be interested in a lateral move to a combat position as their primary job, and 34 percent — or 1,636 — said they would volunteer for a ground combat unit assignment.

Elaine Donnelly of the conservative Center for Military Readiness and a vocal critic of the change said the survey asked the wrong questions and should have been asking if troops favor it and whether it will make a more effective force.

The questionnaire also relied on the “mistaken belief” that training standards will remain the same, which Donnelly said is not realistic given the differing physical abilities between the genders.

She said the Pentagon is bent on imposing gender-based quotas that will drive down standards. Defense leaders say standards will not be lowered.

“The results that are being put out there are designed to manage public perception,” she said. “There is a lot about this that still needs to be discussed and it’s really not fair to the women who serve out there.”

The infantry side is skeptical about how women will perform in their units, and some positions may end up closed again if too few females meet the physically demanding standards of combat, said Gen. James Amos, head of the Marine Corps, who spoke to reporters Thursday at a defense conference in San Diego.

“I think from the infantry side of the house, you know they’re more skeptical,” Amos said. “It’s been an all-male organization throughout the history of the U.S. Marine Corps so I don’t think that should be any surprise.”

Most Marines support the policy change, Amos said.

It will be up to the military service chiefs to recommend and defend whether women should be excluded from any of those more demanding and deadly positions, such as Navy commandos or the Army’s Delta Force.

Over the past decade, many male service members already have been fighting alongside women in Iraq and Afghanistan. Women who serve in supply units, as clerks and with military police have ended up on the unmarked front lines of modern warfare.

More than 150 women have been killed in wars in Iraq and Afghanistan while serving in support roles.

About 7 percent of Marines are female compared to about 14 percent overall for the armed forces.

Both sexes surveyed said getting women closer to the action will improve their career opportunities.