Editor's note: This story was originally published at 12:01 p.m. on Sept. 10, 2015.

All-male ground combat teams outperformed their mixed-gender counterparts in nearly every capacity during a recent infantry integration test, Marine Corps officials revealed Thursday.

Data collected during a monthslong experiment showed Marine teams with female members performed at lower overall levels, completed tasks more slowly and fired weapons with less accuracy than their all-male counterparts. In addition, female Marines sustained significantly higher injury rates and demonstrated lower levels of physical performance capacity overall, officials said.

The troubling findings come as Commandant of the Marine Corps Gen. Joseph Dunford prepares to make a crucial decision regarding the integration of female troops into closed combat roles. Faced with a Defense Department-wide mandate that will open all jobs to women by Jan. 1, he must decide choose whether or not to ask for specific exceptions to the mandate in order to preserve combat readiness. Officials said Dunford had met with Navy Secretary Ray Mabus about the decision but had yet to issue his recommendations.

In a briefing at the Pentagon, officials did not reveal how Dunford plans to act on the task force findings. But they made clear that the Marine Corps was focused on how gender integration would affect overall combat effectiveness, as well as the likely impacts to the health and welfare of individual Marines.

"The true basis of this was to gather some hard qualitative metrics on what we would expect to see in combat effectiveness," said Paul Johnson, the principal investigator for the integration experiment. "Is every member of the group contributing equally to the outcome? That's important to know."

The Marines' Ground Combat Element Integrated Task Force involved about 400 Marine volunteers, roughly 25 percent of whom were women. Over the course of nine months, teams that simulated integrated rifle, weapons, mechanized and artillery units trained to infantry standards and then executed a repetitive series of skills assessments under human testing conditions.

No other military service conducted a similar research experiment. A source with knowledge of Marine Corps planning said the Corps spent about some $36 million in all researching the impacts of combat integration.

While the experiment was closely controlled, there was a key experience gap: Many male task force volunteers came from combat units where they had previously served, while female volunteers came directly from infantry schools or from noncombat jobs. One task force unit, a provisional rifle platoon, attempted to mitigate this problem by comparing the performance of male and female troops who had received no formal infantry training.

The Marine Corps' data findings included the following:

  • All-male squads and teams outperformed those that included women showed higher performance levels than gender-integrated ones on 69 percent of the 134 ground combat tasks evaluated.
  • All-male teams were outperformed by mixed-gender teams on two tasks: accuracy in firing the 50-caliber machine gun in traditional rifleman units and the same skill in provisional units. Researchers did not know why gender-mixed teams did better on these skills, but said the advantage did not persist when the teams continued on to movement-under-load exercises. Gender-integrated teams did out-perform all-male ones in two tasks:
  • All-male squads in every infantry job were faster than mixed-gender-integrated squads in each tactical movement evaluated. The differences between the teams were most pronounced in crew-served weapons teams. Those teams that had to carry weapons and ammunition in addition to their individual combat loads.
  • Male-only rifleman squads were more accurate than gender-integrated counterparts on each individual weapons system, including the M4 carbine, the M27 infantry automatic rifle and the M203 grenade launcher.
  • Even mMale Marines with from the provisional infantry platoon, which had no formal infantry training, outperformed infantry-trained women on each weapons system, at levels ranging from 11 to 16 percentage points.

In a findings briefing sheet, officials also noted that there were tasks female Marines routinely struggled with that posed no similar challenge to their male counterparts.

In scaling an 8eight-foot wall obstacle, researchers they wrote, male Marines would throw their packs to the top of the wall, while female troops Marines "required regular assistance" to do the same. During simulated casualty evacuations involving a 200-pound dummy, mixed-gender-mixed groups were notably slower at the task, except in cases when a single Marine would move the dummy using a fireman's carry. And in those these cases, "it was most often a male Marine who 'evacuated' the casualty," according to the findings analysis.

A team from the University of Pittsburgh recorded athletic and biological data from each Marine task force volunteer before, during and after the assessment. The average differences between male and female participants may explain, in large part, the disparity in overall performance. Among their findings:

  • The average male Marine volunteer was 178 pounds with 20 percent body fat; the average female volunteer weighed 142 pounds with 24 percent body fat.
  • In anaerobic power and capacity, female Marines averaged 15 percent lower levels than their male counterparts. In anaerobic power performance, the top 25 percent of female performers and the bottom 25 percent of male performers overlapped.
  • In aerobic capacity, female Marines demonstrated levels 10 ten percent lower on average than male Marines.
  • Over the course of the assessment, musculoskeletal injury rates totaled 40.5 percent for women, more than double the 18.8 percent rate for men.
  • In all, female Marines sustained 21 "time-loss" injuries which took them away from task force duties for a day or more. Nineteen of the women's injuries were lower extremity injuries and 16 percent took place during a task that required movement while carrying a load. Officials said they could not immediately provide the comparable injury rates for men but said lower extremity injuries were the most common among male Marines as well.

Col. Anne Weinberg, deputy director of the Marines' Force Innovation Office, said it was important to note that the experiment only evaluated the performance of mixed-gender teams under current conditions. It was a measurement, she said, of how well average female Marines were doing today, not how well they could perform under ideal circumstances and with better training.

"I would characterize this as: There's more to be learned," Weinberg said. "There's an opportunity to train and become stronger and to execute these tasks in a more lethal manner."

High injury rates among women were also a problem at the Infantry Training Battalion, the Marines' basic infantry training school for enlisted troops that temporarily opened to women between 2013 and 2015. Researchers found that female ITB participants were injured at more than six times the rate of male participants, and nearly one-third of their injuries occurred during movement-under-load tasks, while just 13 percent of male injuries did.

Overall, women graduated ITB with a 36 percent success rate during the evaluation period. Male Marines had a 99 percent graduation rate during that same window.

Female Marines fared much better in ground combat schools for other occupational specialties, indicating that jobs placing less emphasis on marching with heavy packs than rifleman and weapons specialties do may be more conducive to gender integration. The artillery cannon crewman course had the same graduation rate — 86 percent — for men and women during the evaluation period. In the tanks and amphibious assault vehicle crewman courses, women had a 71 percent graduation rate, compared to 99 and 94 percent for men, respectively.

While Johnson did not reveal overall attrition rates for the integrated task force ahead of a full release of data expected to take place later this month, task force volunteers told Marine Corps Times that artillery and mechanized vehicle units had low injury rates, and physical tasks for these jobs presented less of a challenge than marching with a rifleman's assault pack did.

It's not certain how to explain the disparity in weapons accuracy rates between the genders, though it may have its roots in training. As Marine Corps Times reported earlier this summer, the gender-segregated battalion that trains all female recruits at Parris Island, South Carolina, had historic rifle qualification rates nearly 20 percentage points lower than the three male recruit training battalions until a series of command initiatives and the leadership of a former battalion commander, Lt. Col. Kate Germano, caused qualification rates to soar from 79 percent to 91 percent in just a year.

It remains unclear how all these data findings will affect the ultimate gender-integration process for the Marine Corps. Even if Dunford does request that certain infantry jobs remain closed to women for reasons tied to combat effectiveness, his request may be overridden by Mabus or Defense Secretary Ash Carter, who will govern implementation of the Jan. 1 integration order.

For the Marine Corps, this decision will be made in the wake of recent announcements by other service leaders of their intent to open specialized combat roles to female troops.

Late last month, the Army graduated the first two female officers from its elite Ranger school. While Ranger units remain closed to women, Army Secretary John McHugh has since announced that the school will remain open to all qualified women.

Meanwhile, outgoing Chief of Naval Operations Adm. Jonathan Greenert said in an August interview that women should be allowed to serve as SEALs if they can pass the grueling six-month training course. Mabus, who will play a key role in the Marines' integration process, told Navy Times this month that he "sees no reason" to ask for an exemption to the integration mandate.

If the Marine Corps chooses not to ask for exceptions, the task force data will be used to inform new MOS-specific gender-neutral entry standards the Corps is expected to roll out later this month. With the University of Pittsburgh research, officials have abundant information that can be used to determine the physical characteristics of successful infantry Marines in every specialty. However, Johnson said, the self-selecting nature of the task force population made it difficult to isolate an ideal female infantryman, in terms of build or performance capacity.

"What are the traits of this gender that were able to perform well?" Johnson said. "The honest answer is, we were not able to find that."

For groups and organizations committed to allowing women the opportunity to fill combat roles, the Marines' new data findings may not provide much pause. Mary Kate Cunningham, a spokeswoman for the coalition No Exceptions 2016, told Marine Corps Times in an earlier interview that no findings from the task force would change the group's position that female troops should be allowed in every job.

"When the Marine Corps changed from a dead hang to a pullup [in its Physical Fitness Test], it took 15 years for men's scores to return to a high," Cunningham said. "Those young women will train for these physically demanding jobs. People will meet standards."

The idea The perspective of No Exceptions 2016 -- that the military will be stronger with the largest possible pool of people able to compete for each job from groups like No Exceptions 2016 will come up against the Marine Corps' philosophy of promoting the best overall unit performance as an integration decision draws near.

"The Marine Corps fights as units," researchers wrote in their findings brief. "Therefore, developing and maintaining the most combat effective units must always be at the forefront of any contemplated institutional change."

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