Related: Marine Corps' intention to bar women from combat roles at odds with Navy
The same critics said the corps’ decision to release only a four-page summary of its study, which focused on negative aspects of women as Marines while keeping the bulk of the study under wraps, was “hugely problematic”.
One of the report’s released conclusions found that: “The integration of females … will add a level of risk in performance/effectiveness and cost … The bottom line is that the physiological differences between males and females will likely always be evident to some extent.”
But other pages from the report, seen by the Guardian, indicate that women were not expected to pose problems for ground-combat units, so long as clear standards, diligent screening of candidates and good training and leadership were in place.
According to the data shared with the Guardian, the study also showed that some women excelled during tests such as hiking quickly with heavy loads and firing artillery under simulated enemy attack, while mixed Marine units showed superior morale and problem-solving and better discipline than units composed only of male Marines.
Furthermore, though the report found all-male units were better at hiking, shooting, gorge-crossing and cliff-climbing, and males suffered fewer injuries, in one section of tests a mixed-sex unit out-marched three all-male units, progressing at five kilometres an hour (kph). The Marine Corps requirement is 4kph, carrying heavy packs and equipment.
Elsewhere, the study found that gender integration across all units would “bring with it many of the general benefits of diversity that we experience across the spectrum of the workforce”.
The Marine Corps based its conclusions on averages, according to which women displayed poorer physical capability and target shooting averages than men, even though some individuals outperformed their male counterparts.
“The Marine Corps has always been looking for data that would justify continued exclusion of women from the infantry,” said Ellen Haring, a retired Army colonel and senior fellow at the equality lobbying group Women in International Security. “This study was fundamentally flawed.”
Haring added: “The way this study has been presented is hugely problematic. The four-page extract, undated, unsigned, was circulated around on Capitol Hill, I think looking for political support from members of Congress for continuing to exclude women. And the bulk of the data not being released.”
The Marine Corps has declined to comment on the leaks from its study.
The unofficial disclosure of key details of the gender comparison trials is likely to deepen the rift between the Obama administration’s Secretary of the Navy Ray Mabus and Joseph Dunford, who was the commandant of the Marine Corps until he rose to become head of the Joint Chiefs of Staff in September. The two have clashed over the study and the issue of gender integration.
The Marine Corps is believed to be the only branch of the US military to have recommended to the government it be excluded from the new defense policy, set to come on stream in 2016, that will open all combat roles to women.
Military heads submitted their recommendations on integration to Defense Secretary Ashton Carter earlier this month. He will announce his decision by the end of the year.
“I have no doubt that if you have valid standards – not lower ones – that there will be women who can meet those standards,” Haring said.
“It’s not about how many women can make it through to the Marines infantry, for example: it’s the fact that they are given an equal opportunity to compete for those jobs that is crucial.”
Haring and University of Sydney researcher Megan MacKenzie, author of Beyond the Band of Brothers: the US Military and the Myth that Women Can’t Fight, were leaked the conclusions and 380 pages of the Marines’ study after uproar greeted the four-page summary on its release in September.
They believe the findings have been submitted to the government as part of the Marines’ argument against allowing women access to frontline infantry and reconnaissance units. Haring dismissed the Marine Corps’ study as biased from the start.
“If women are not capable, of course I have no problem with them being excluded,” she said. “But you need to set the standards and then whatever soldier or Marine meets them, they are the ones who should get the places in the units.”
The trials took place between 2013 and 2015, using 400 volunteers, of which 100 were women. They underwent selection, training in North Carolina and then combat-exercise testing in California, split into all-male and male-female clusters.
After studying the data, MacKenzie said that overall, “there were some women who performed as well as the men and some outliers who blew away the men’s performance.”
MacKenzie, a Canadian academic based in Australia, takes special interest in gender integration in the armed forces of the US and other nations. On her website, she published an analysis of the 380 pages of data she and Haring obtained.
“The Marine Corps acknowledged that women do not have a negative impact on unit cohesion, contrary to some arguments you will hear,” MacKenzie told the Guardian. “And if they had done proper physical screening, the women who were injured would not have been included in the study from the outset.”
MacKenzie also objected to the fact that the male Marines in the study had more combat-training experience than the women.
The Marine Corps reviewed Canadian, Australian, Israeli and British military results during its study, all of which results except the British supported women being eligible for all combat roles.
Haring said the fact American women have been effectively in combat during more than 13 years of conflict in Iraq and Afghanistan, dying under hostile fire and bombs and winning bravery medals, has had a positive effect on respect and career prospects for women across the military.
But women serving under orders on the frontline still violates US government policy, an issue which was only addressed when then-Defense Secretary Leon Panetta announced in early 2013 that the government intended to open up combat roles to women.
The various branches of the US military had until 1 October this year to request exemption before the new rules go into effect in 2016.
Related: Women in combat: US military officially lifts ban on female soldiers
In August, two women qualified as Army Rangers, regarded by many as the toughest Army unit. A third qualified in October, and Haring was attending a celebratory lunch for her at Fort Benning, Georgia.
“Many men have never served with women, but when they do, many of them become their biggest advocates,” she said.
“I recently received an email from a young lieutenant who did not make the grade in the infantry, telling me he had not thought women were up to it until he saw them in action and saw them excelling, where he had not made it.”
The Navy SEALs announced in August that they would allow women to apply. Other special operations units have been gradually opening up to women.
But the Marine Corps is regarded as one of the strongest bastions of maleness in the US military. The Marine Corps report acknowledged that “ground combat units have many years of historical bias, much of which will take time to eliminate”.
One point buried in the corps study and now highlighted by some sources states that among the study group there were reports of seven sexual assaults, though it was not specified at what point in each of the relevant Marines’ careers the reports were made or what they involved.
Even if it is assumed that all of the alleged victims of such assaults were among the female Marines, that is not an unusual rate of reports of sexual misconduct in the military, MacKenzie said.
She added that the statistic even refuted the notion that women would be at elevated risk of being raped if they were serving at close quarters with men in a combat environment.
“The military has a sexual assault problem, but the solution is not keeping women out, it’s dealing with the sexual assault problem,” MacKenzie said.
Haring, who retired as a colonel after 30 years in the military, sued the Defense Department in 2012, alleging she was denied a job on the frontline in Afghanistan after being told on the eve of her deployment she “wasn’t qualified”.
She withdrew the lawsuit after Panetta announced the end of the official ban on women in combat.
“I wasn’t looking to get anything out of the lawsuit except a change of policy,” she said. “I wanted to make the military more welcoming to women.
“I have a good, fulfilling career, but I just think the military will be better off if it selects the most capable citizens to serve.”