Women in the U.S. military have been flying warplanes for years, and recently began serving in artillery and tank units. But they're still barred from direct ground combat.
Now, for the first time in the course's 35-year history, the Marine Corps is putting the first women through its grueling Infantry Officer Course: 86 days crawling through obstacle courses, lugging heavy machine guns, navigating the woods at night.
Col. Todd Desgrosseilliers, the top trainer at Marine Base Quantico in Virginia, says there's a good reason the course is so tough that 1 in 5 Marines fail.
"These officers, these lieutenants are going to go out there and lead platoons of enlisted Marines on the battlefield," he says.
The official reason for the prohibition against women in combat roles stems from "job-related physical requirements" that would exclude the vast majority of women.
No Slack For Anyone
On the first day of the training course, it's pitch-black when dozens of Marine lieutenants spill out of their trucks, along a dirt road.
They drop to their knees, pull out their compasses and open their maps under the red glow of a headlamp. They must navigate to three locations and then meet up at a precise time. Within minutes, they all disappear into the wet and tangled woods.
Hours go by.
As the sun rises, the first of the 109 Marines participating in the course emerge from the woods. They jog down a road with their 20-pound packs and assault rifles.
One of the Marines wears her blond hair pulled back into a tight bun. Her face is covered in sweat as she reaches the rallying point and approaches the instructors.
"You realize you're late?" one of the officers tells her. "Two minutes, 30 minutes, at this point it doesn't matter."
She's three minutes late. No one gets any slack not the women, not the men, some of whom are still trotting in.
She turns and heads off to her next event in this combat endurance test that will stretch well into the night.
Physically And Psychologically Grueling
The 24-year-old, stocky young woman is a Marine lieutenant and college athlete from the Southwest. The only other woman in this course, a 33-year-old officer from the West Coast, is a serious distance runner.
The Marine Corps won't disclose their names. The women have been promised anonymity for volunteering to take part in this research study.
Eventually, the Marines hope to have 100 female volunteers to see how many if any can pass this tough test that's required of all Marine infantry officers.
The Marines are never told what will come next. Capt. Brian Perkins says that's part of the plan. Combat is always uncertain, and officers need psychological stamina along with physical strength.
"You don't have to be in the absolute best shape of your peers coming here," Perkins says. "But if you're mentally tough, you can outlast a lot of guys."
They may be asked to reassemble an M-16, or fix a radio, or do squats, push-ups and pull-ups seven hours into the test under Perkins' critical eye.
He watches the 24-year-old officer as she does pull-ups.
"She doesn't look any different than the men so far," he says.
The other woman, the 33-year-old officer, can barely do one.
Another officer comes over to show her the right way to do a pull-up. That officer Maj. Scott Cuomo is in charge of the course and fought in Iraq and Afghanistan. Upper-body strength, he says, helps Marines in combat climb over walls or pull themselves out of canals.
On a standard patrol, Cuomo notes, a Marine carries 70 to 80 pounds of gear.
"You need the strength. If you got it, great," he says.
'Stay Motivated, Ma'am'
Later, the Marines are in a long line waiting to sign up for one of the most rigorous parts of the course. The Marines asked NPR not to describe it, but it involves hand-to-hand combat and is very violent.
An officer tells them to take off their packs, empty everything out of their pockets and grab a mouth guard. They divide into twos.
There's a tangle of bodies, grunting, swearing. An instructor stands over the Marines.
One woman, the one who couldn't handle the pull-ups, quickly loses her match. The other woman holds her own against a male Marine. The match ends in a draw.
Even so, the instructor is disgusted. It's evident in his voice when he tells them to hurry up and climb into a waiting truck.
The woman who fought to a draw finds a friendlier Marine at the next event, who offers encouragement: "Stay motivated, ma'am."
She seems motivated as she trots away with her assault rifle. She survives this 16-hour day. The other woman failed, along with 26 men a quarter of the class.
As for the woman who made it through the first day, she told Marine leaders that she wants to try to open a door for women after her.
Now she's got just 85 more days of training.