An experimental Marine Corps study obtained by the Monitor has concluded that units with both men and women are less effective than all-male units.

The results of the experiment, known as the Ground Combat Element Integrated Task Force (GCEITF), could be used by the Marines as grounds to ask for an exemption to the combat exclusion policy, which currently bars women from taking part in direct combat.

The services have until January to open all jobs to women, or ask Pentagon leaders for an exemption by October.

The GCEITF included roughly 200 male and 75 female volunteers, who were evaluated on how they performed a series of physical combat tasks between March and May.

The results of the study come on the heels of news last month that two women passed the Army’s grueling Ranger School and earned their Ranger tabs.

The Marine Corps’ conclusions have sparked criticism from female Marines and others, who argue that the study was poorly conducted and biased toward a belief that men are biologically and psychologically built to be better fighters.

Indeed, efforts to integrate combat units constitute “social engineering,” Lt. Gen. Gregory Newbold, a former Marine infantryman who served as Director of Operations on the Pentagon’s Joint Staff before he retired, argued in an op-ed this week that was widely seen as laying the groundwork for the Marines’ experimental task force study release.

In introducing its conclusions, the Marine Corps cites the “the brutal and extremely physical nature of direct ground combat, often marked by close, interpersonal violence.”

It further argues that the nature of battle “remains largely unchanged throughout centuries of warfare, despite technological advancements.”

Mr. Newbold echoes similar points, citing “the burden of 30 to 80 pounds of personal equipment, mind-bending physical exertion, energy-sapping adrenaline highs, or the fact that the threadbare clothes you wore were unchanged for over three weeks and may have been 'scented' by everything from food, to blood, dysentery, and whatever was in the dirt that constituted your bed. And don’t forget insects of legendary proportion and number,” he adds in his op-ed, published by the War on the Rocks, a highly-regarded military blog.

“More importantly,” Newbold argues, are the bonds with comrades who experienced the “shared duties of clearing the urinals, the pleasures of a several nights of hilarious debauchery, and multiple near-death experiences – a comrade in arms who has heard more about your personal thoughts than your most intimate friends or family.”

Though Newbold acknowledges that the two women two who recently passed Ranger School are “worthy role models,” he warns against “the cost of sexual dynamics in a bare-knuckled brawl, amidst primeval mayhem.”

Women don’t belong in such a world, Newbold argues, concluding, “If I’m wrong, the cost may be denied opportunity to strong and impressive young women. If you’re wrong, our national security is shaken and there is a butcher’s bill to pay.”

The op-ed was published one day before the Marine Corps was set to role out its own study, which found that “All-male squads, teams and crews demonstrated higher performance levels on 69 percent of tasks evaluated ... as compared to gender-integrated squads, teams and crews.”

The study also concludes that all-male squads were faster and had greater accuracy in firing weapons.

Finally, it concludes that all-male crews “had a noticeable difference in their performance of the basic combat tasks of negotiating obstacles and evacuating casualties.”

The study cites a wall obstacle specifically. “Male Marines threw their packs to the top of the wall, whereas female Marines required regular assistance in getting their packs to the top.”

The study also cites the basic stats of the participating troops, which included men who averaged 178 pounds in weight with 20 percent body fat, and women who averaged 152 pounds, with 24 percent body fat.

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The study concludes that “females possessed 15 percent less power than males,” and that “the female top 25th percentile overlaps with the bottom 25th percentile for males.”

Women also were more likely to be injured, according to the study.