By Mark Thompson
December 3, 2015

A bomb ripped through a U.S. armored vehicle patrolling a Baghdad street in the darkest days of the Iraq War, setting it ablaze and filling the crew compartment with smoke. As flames licked the fuel tanks, busted hydraulics kept the hatch locked. Amid the carnage and choking, the four soldiers trapped inside heard enemy small-arms fire hitting their 18-ton Stryker. After finally getting the hatch open, a lieutenant pulled out a staff sergeant who had lost his leg below the knee. That left two people inside: a grievously wounded 6-ft. 1-in. sergeant, 250 lb. in his gear, and a 5-ft. 2-in. soldier weighing half as much.

“She pulls him out of this burning vehicle, which is amazing in itself,” her commander recalled. “Getting in and out of the vehicle with all of your kit on is difficult enough on its own, especially if you add smoke, fire and the chaos of getting shot at, and bullets pinging off the outside of the armor, but she does it anyway,” he continued in an interview for an Army history project. “As she’s dragging him back, she’s shooting one-handed with her M-16 toward the bad guys. Completely phenomenal! She’s just f-cking awesome!”

The woman wasn’t an infantryman but an Army lab technician who spent most of her time spinning vials of blood back at the unit’s base, not trying to kill rooftop attackers 100 yards away. But on that grim day in 2006, her commander didn’t care. While she had come along on the mission in case female Iraqis needed to be searched, she proved capable of far more than that. “It changed my opinion about where women ought to be in the fight,” he said. “When the chips are down, a good soldier is a good soldier.”

Good enough to be assigned to the toughest combat jobs in the U.S. military? That’s the historic question now pending inside the Pentagon. A generation ago, the possibility of women serving on the front lines seemed as unlikely as, well, a female President. Now both could happen in 2016.

Women have been advancing toward the front lines for more than a generation. They climbed into Air Force fighter-jet cockpits in 1993 and aboard Navy submarines in 2011. But when it comes to combat on the ground–generally the dirtiest and bloodiest jobs in any military, and a required ticket-punch for ground-force promotions–progress has been slow. Women have been edging closer by serving in intelligence, logistics and other support roles. But in 2013 then Defense Secretary Leon Panetta ordered a review of the physical demands of combat slots and any justification for the Pentagon’s policy that keeps women out of front-line combat billets. Defense Secretary Ashton Carter is expected to decide in January if women should be permitted in all military roles, including the ones reserved until now for brothers–not sisters–in arms: the infantry grunts, those riding tanks and artillery into battle, and special operators.

The Air Force and Navy, which do little fighting on the ground, have already opened up 98% of their slots to women, and their uniformed leaders have approved going all the way. But that has been a relatively easy choice compared with the decision to add women to the ranks of combat infantry in the Army and the Marines. While the Army, which currently allows women in 82% of its jobs, is green-lighting all jobs for women so long as they can meet certain physical standards, the Marines are holding out, Pentagon officials say. Marine ground-combat units, which make up 25% of Marine slots, should remain all-male bastions, according to recommendations from corps officials. “Women don’t have the brute strength that’s needed in combat,” says Jude Eden, a woman who served as a Marine sergeant in Iraq for seven months in 2005 and 2006. A Marine study last summer reported that 13% of female Marines were injured in infantry training, compared with 2% for men. “And women’s higher injury rates certainly don’t add strength to combat units,” she says.

Advocates of preserving the status quo cite the life-and-death brutality of close-in combat–blood-spitting, skull-splitting fights with knives, rocks and bare hands. A tidy concept like fitness doesn’t touch the gory reality. “There is a monumental difference between fitness,” a Marine major wrote in a 2013 study, “and fighting in a hand-to-hand match to the death.” Even advocates of opening combat to women concede that the average male military recruit is stronger and faster than the average female military recruit. (Gender-specific physical standards acknowledge the fact: a 22-year-old male soldier has to run 2 miles in no more than 17 min. 30 sec.; his female comrade gets 20 min. 36 sec.).

But plenty of women are above average, and some are extraordinary. If the military wants the best available troops fighting the nation’s wars, argue supporters of opening combat ranks to women, it can’t rule out half the population.

THE ARMY’S APPROACH

Three women have passed the Army’s punishing Ranger School course in recent months, but few assignments require such intense tests. That’s about to change. The prospect of women serving on the front lines led Pentagon civilians to order the military to draft physical-fitness standards for each military job. Generally speaking, it will be easier for men to meet such standards: assessments of the Army’s storied 101st Airborne Division found that the average female weighed only 80% as much as the average male, with 10% more body fat and 30% less muscle.

But the military is more than muscle, some advocates argue. On average, men are more aggressive, which can be beneficial in combat. But that trait also contributes to more accidents and injuries, as well as suicides. Women are smaller–their stride is shorter, requiring them to march faster to cover the same terrain. And they may be more susceptible to injury: from 2001 to 2012, female troops were medically evacuated from Afghanistan at a rate 22% higher than men, even though they were formally barred from ground combat. In 2014, female troops were hospitalized 40% more often than men, even after eliminating pregnancy from the calculation. At the same time, the Marines’ own research shows that mixed-gender units solve problems better and have fewer disciplinary headaches than all-male outfits.

“Units would be better off by having women in them,” says David Barno, a retired three-star Army general who commanded all U.S. troops in Afghanistan from 2003 to 2005. “You get a better product when you’ve integrated men and women on staff, and when you’ve got women commanders.” Nonetheless, if women end up on the front lines, “it’s going to be a significant emotional event,” Barno says. “You’ve got rifle squads and Marine infantry companies full of 18-year-old football players just out of high school, and there weren’t any women on that football team–that’s the psychology of a rifle squad full of young men.”

Physical-fitness standards may eliminate a greater percentage of women than men, but they will also assure that all ground troops are up to the task regardless of gender. In the past, simply being a man was good enough. Standards, when they existed, were flimsy. “We kind of had good-ol’-boy, ‘It’s a road march at this speed,'” explained Lieut. General Bob Brown, who is responsible for Army leadership development, at a September gathering in Fort Benning, Ga. Anyone who can meet the new standards should be allowed to serve, he said.

“There will probably be some male soldiers in the infantry today that don’t measure up, don’t qualify to be the infantry,” added the commander of the Army’s 18th Airborne Corps, Lieut. General Stephen Townsend. “That’s O.K. with me. It’s also O.K. with me if there are female soldiers who qualify.”

THE MARINES RESIST

In contrast with the Army, the Marines have dug in behind the idea that front-line units should remain all-male. “To move forward in expanding opportunities for our female service members without considering the timeless, brutal, physical and absolutely unforgiving nature of close combat is a prescription for failure,” an internal Marine study completed in August concluded. “Those who choose to turn a blind eye to those immutable realities do so at the expense of our corps’ war-fighting capability and, in turn, the security of the nation.”

Gregory Newbold, a retired Marine lieutenant general, says that physical strength is only part of the combat calculus. If there is a time for men to be brutes, this is it. “Crude traits are kind of useful,” he says of testosterone-laden camaraderie. “It’s important that ISIS or [Vladimir] Putin knows the other side can be ruthless.” And he says he worries that the sexual dynamics inherent in adding women to the front lines would dilute combat power.

In its key tests, the Marine Corps pitted all-male squads against mixed-gender units through nine months of assessments involving 350 Marines, including 75 women. All-male squads did better than mixed-gender units in 93 of 134 events. Mixed-gender units outdid their all-male counterparts in just two. There were no significant differences in performance in the other 39 events. “The majority of the operationally relevant differences occurred in the most physically demanding tasks, such as casualty evacuations, long hikes under load, and negotiating obstacles,” an internal Marine assessment said. Infantry tasks, in other words.

Brenda “Sue” Fulton, a former Army captain, says the tests were designed to produce lopsided results. The women in the mixed units weren’t trained to the level of their male counterparts. “The Marines are tossing women into the deep end of the pool and saying, ‘Compete with the varsity swim team,’ ” she says. The corps has “very low expectations” of its women because of “an institutional belief that women simply are not up to it,” adds Fulton, a 1980 West Point graduate who chairs the academy’s Board of Visitors.

The Marines do agree with the Army on one thing: the new standards will be a welcome chance to weed out male recruits who can’t meet the demands of the infantry. Fitness tests “will serve to reduce some of the ‘wastage’ that occurs in our ground combat arms units due to Marines being physically incapable of meeting the demands of service,” another internal Marine report said.

DECISION TIME

Other nations, including Canada, Denmark, Germany and Norway, permitted women in combat beginning in the 1980s. Canada experienced no “negative effect on operational performance or team cohesion,” a 2009 study found. But their presence is minimal. That’s because many women–like many men–have no desire to risk their lives. Women account for fewer than 1 of every 100 soldiers in the Canadian army’s infantry units. (They comprise 3% of the tanker force and 5% of artillery.)

Low numbers complicate the challenge of integrating women. Ample research supports the idea that lasting change requires an as-yet-unspecified critical mass of women serving in combat units. “One of the biggest challenges from an implementing point of view will probably be the tyranny of small numbers,” says General David Perkins, the Army’s top trainer.

Opening the combat ranks will also raise a couple of thorny legal issues: registration for the draft, and involuntary assignment to combat units. Women currently don’t face either of these prospects. While the chance of a draft is unlikely, all men in the U.S. are required to register with the Selective Service when they turn 18. Because Congress ordered the registration of “male persons,” it would have to pass new legislation if it wanted to include women.

And if women seek to take the final step toward full participation in the military, it hardly seems fair that they should be able to say “No thanks” if they’re needed to fight. “Are we willing to cause women to serve in infantry units against their will, as we do men?” asked retired admiral Eric Olson, chief of U.S. Special Operations command from 2007 to 2011, at a July gathering. “About 30% of infantry units are men who didn’t volunteer to be in front-line combat.”

For now, it’s unusually quiet on the Washington front. Defense Secretary Carter issued a directive on Oct. 2 instructing the military to remain mum as he mulls the divergent recommendations. But he seemed to tip his hand when he said in September, “Everyone who is able and willing to serve and can meet the standards we require should have the full opportunity to do so.”

Pentagon officials believe that Carter, who never served in the military, will overrule the Marines’ objections when he issues his decision. And the men of the corps will be expected to perform that time-honored acknowledgment of authority: a salute, along with a “Yes sir!”

Contact us at editors@time.com.

This appears in the December 14, 2015 issue of TIME.

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