Marine Corps Study Casts Doubt on the Success of Gender-Integrated Units

— -- A new Marine Corps report highlights the complexity of integrating women into combat units, a process that could happen early next year. But first, Defense Secretary Ash Carter must decide if some roles should remain closed to women, which, so far, only the Marine Corps has recommended should be the case for its combat units.

To guide its recommendation, the Marine Corps conducted a nine-month study to understand how gender-integrated units performed in comparison to the traditional all-male units.

The test unit, known as the Ground Combat Element Integrated Task Force (ITF), was made up of 300 male Marines and 100 female Marines who trained together to simulate their performance in a deployment. Their performance was compiled into a 1,000-page study that has not been released, though the Marine Corps has released a four-page summary that demonstrated that all-male units outperformed the integrated unit.

All-male squads demonstrated higher performance levels on 69% of tasks evaluated compared to gender-integrated teams and were found to be faster and more accurate with weapons.

The summary went on to say that all-male teams outperformed gender-integrated ones on “basic combat tasks of negotiating obstacles and evacuating casualties.” Furthermore, female Marines had higher injury rates compared to males performing the same tasks.

But a 103-page portion of the actual report provided to the Washington Post by researchers advocating for gender-integration in the military paints a more complex picture of the conclusions presented in the summary.

While all-male units significantly outperformed integrated ones, integrated groups excelled at complex decision-making. The report found that adding women to the unit also improved the behavior of the group as a whole.

“Integration of females is likely to lower the instance of disciplinary action, and this has been shown in general across the Marine Corps,” the report said.

But the document also found that seven sexual assaults were reported by members of the unit, though the study noted that Marines in the ITF reported sexual assault “at levels similar to those in other military populations.”

The findings will be analyzed by Defense Secretary Ash Carter, who is expected to make a decision by the end of the year on whether to open all combat roles to female service members. Each service unit gave its recommendation to Carter at the end of September. U.S. officials have told ABC News that the study’s conclusions contributed to the Marine recommendation that women should continue to be barred from its combat positions.

Navy Secretary Ray Mabus pointed out to NPR that while the Marine Corps report points out women could not carry heavy loads for as long as men, there were women who could. He also challenged the conclusion of injury rates, telling NPR, “part of the study said that we’re afraid that because women get injured more frequently, that over time women will break down more -- that you will begin to lose your combat effectiveness over time. That was not shown in this study. That was an extrapolation based on injury rates, and I’m not sure that’s right.”

Ellen Haring and Megan MacKenzie, the researchers who obtained the documents for the Washington Post, called the study “inherently flawed.”

“Significantly, the unclassified yet previously unreleased research documents indicate that women do not negatively impact unit cohesion, that the study sought to measure the impacts of integration in the absence of established combat standards, that female volunteers in the study had no operating force experience in ground combat units, and that better physical screening would have all but eliminated the rates of injury for women,” they wrote in an essay posted Tuesday.

ABC News' Luis Martinez contributed to this report.