The research was carried out by the service in a nine-month long experiment at both Camp Lejeune, N.C., and Twentynine Palms, Calif. About 400 Marines, including 100 women, volunteered to join the Ground Combat Element Integrated Task Force, the unit the Marine Corps created to compare how men and women do in a combat environment.

“This is unprecedented research across the services,” said Marine Col. Anne Weinberg, the deputy director of the Marine Corps Force Innovation Office. “What we tried to get to is what is that individual’s contribution to the collective unit. We all fight as units… We’re more interested in how the Marine Corps fights as units and how that combat effectiveness is either advanced or degraded.”

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The study, an executive summary of which was released Thursday, was carried out as all the services prepare to submit recommendations to Defense Secretary Ashton B. Carter this fall on whether any jobs should be kept closed to women. In a landmark decision in January 2013, then-Defense Secretary Leon Panetta rescinded a decades-old ban on women serving in combat jobs like infantry, but gave the services until this fall to research how they wanted to better integrate women and if any jobs should be kept closed.

The Pentagon faces increasing pressure to fully integrate women, following the historic Aug. 21 graduation of two female officers from the Army’s Ranger School. The legendarily difficult school was opened on an experimental basis this spring, with 1st Lt. Shaye Haver, 25, and Capt. Kristen Griest, 26, completing the requirements. Sixteen other women who attempted the course failed, while one other woman remained in the school’s third and final phase at Eglin Air Force Base as of last week.

The Marine Corps’ research will serve as fodder for those who are against fully integrating women. It found that all-male squads, teams and crews demonstrated better performance on 93 of 134 tasks evaluated (69 percent) than units with women in them. Units comprising all men also were faster than units with women while completing tactical movements in combat situations, especially in units with large “crew-served” weapons like heavy machine guns and mortars, the study found.

Infantry squads comprising men only also had better accuracy than squads with women in them, with “a notable difference between genders for every individual weapons system” used by infantry rifleman units. They include the M4 carbine, the M27 infantry automatic rifle (IAR) and the M203, a single-shot grenade launcher mounted to rifles, the study found.

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The research also found that male Marines who have not received infantry training were still more accurate using firearms than women who have. And in removing wounded troops from the battlefield, there “were notable differences in execution times between all-male and gender-integrated groups,” with the exception being when a single person—”most often a male Marine” — carried someone away, the study found.

The full study is more than a thousand pages long, Marine officials said. They anticipated publishing it online in coming days.

A physiological assessment carried out by the University of Pittsburgh’s Neuromuscular Research Laboratory found that the average man in the experimental integrated unit weighed 178 pounds with 20 percent body fat, while the average woman weighed 142 pounds with 24 percent body fat.

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Researchers hooked men and women alike up to a variety of monitors, and found that the top 25th percentile of women overlapped with the bottom 25th percentile of men when it came to anaerobic power, a measure of strength, Marine officials said. Those numbers were expected to a degree given the general size difference between the average man and woman.

The gender-integrated unit’s assessment also found that 40.5 percent of women participating suffered some form of musculoskeletal injury, while 18.8 percent of men did. Twenty-one women lost time in the unit due to injuries, 19 of whom suffered injuries to their lower extremities. Of those, 16 women were injured while while carrying heavy loads in an organized movement, like a march, the study found.

The kinds of injuries varied, too: The majority of women in the unit who lost time due to injuries suffered through hip problems, with foot and toe injuries also problematic. In men, the most common injuries were to the feet and toes, followed by the ankles, Weinberg said.

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The research raises the question whether the Marine Corps may press to keep the infantry and Special Operations, in particular, closed to women. If they do so, they could face resistance from above: Navy Secretary Ray Mabus, who oversees both the Navy and Marine Corps, already has indicated that he sees no reason to keep the infantry closed to women.

“That’s still my call, and I’ve been very public,” Mabus said in a Sept. 1 interview with the independent Navy Times. “I do not see a reason for an exemption.”

Ellen Haring, a reserve Army colonel and vocal advocate for fully integrating the military, said the results of the Marine Corps’ research are not surprising. The service was told to assess how individual women do in combat situations, but the task force instead assessed groups with average female Marines — rather than high performers — in them.

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“They’re always coming up with these averages,” Haring said. “‘The average woman can’t do what the average man does. I don’t think that’s a surprise to any of us. But they weren’t told to do this based on averages. It has to be based on individual capabilities.”

A Marine Corps veteran who has advocated for full integration, Katelyn van Dam, also took issue with the study, saying it is time to stop asking if women can “hack it” in combat units and instead focus on developing gender-neutral standards that apply to all. She is a spokesman for the Truman Project and Center’s No Exceptions initiative, which calls for opening all military jobs to women immediately.

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“It has been scientifically proven that overall physical fitness — not gender — correlates to injury,” she said. “While the methodology and data from the Task Force has not been made available to us, we do know that female participants only had to meet the physical requirement of passing a third-class male physical fitness test, and that most came directly from the schoolhouse or non-combat jobs. Thus, their participation was based on old standards.”

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Female Marines previously struggled heavily at the Infantry Officer Course (IOC), a grueling school at Quantico, Va., at which the service trains lieutenants to lead infantrymen in combat. All 29 women who attempted the course failed, mostly in the initial Combat Endurance Test, an exhausting exam that includes everything from land navigation to swimming in combat gear. By comparison 71 percent of the 978 men who took the course in the same time frame passed. The school was first opened on an experimental basis to women in 2012, ahead of Panetta’s landmark decision.

The service also opened its enlisted infantry training at Camp Geiger, N.C., to women. They have performed a better than those at IOC: Between September 2013 and June 2015, 144 of the 401 female volunteers (36 percent) passed the course, Marine officials said. By comparison, 5,448 of 5,503 men (99 percent) passed, according to the executive summary released Thursday.

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