– First Lt. Marina Hierl watched a dozen Marines charge toward human silhouettes made of paper atop a hill. Despite the early hour, the troops’ armored vests and camouflage uniforms were soaked with sweat. She stood back as they scrambled up the incline, shouting and firing rifles.

“Push left,” she said after the squad completed its mock attack and assembled around her. “And make sure you’re communicating.”

It was a fairly routine instruction to Marines training for war, coming from a lieutenant in a role familiar to the men: a young, college-educated officer who had little experience but had direct oversight of their lives.

But Hierl is the first woman in the Marine Corps to lead an infantry platoon — a historic moment for a male-dominated organization that had fiercely opposed integrating female troops into combat.

That dynamic has been playing for months inside Echo Company, a group of 175 Marines and Navy sailors sent to the Northern Territory of Australia for roughly six months of training exercises and to act as a response force for the Pacific region.

Hierl is one of four platoon commanders in Echo Company. Her presence, first eyed with skepticism, appears to have been quietly accepted.

Thirty-seven women have attended the Marines Corps’ Infantry Officer Course at Quantico, Va., for 13 weeks of combat evaluations and mileslong hikes carrying heavy loads. Only two women have passed.

Of those two women, only Hierl has been given a platoon of roughly 35 men to lead.

Capt. Joshua J. Pena, a spokesman for the Marines’ Training and Education Command, said that the men and women attending the Infantry Officer Course are evaluated by the same standards and are provided an “equal opportunity to succeed.”

Last fall, Hierl was among the handful of new lieutenants who reported to duty with the 2nd Battalion, 4th Marines at Camp Pendleton in California. The battalion is made up of about 1,000 troops divided into five companies, including Echo.

When the commanding officer of Echo Company, Capt. Neal T. Jones, learned that Hierl had been assigned to the battalion, he asked that she be sent to his unit. “If you’re the first to do something, that implies you have so many positive traits,” he said. “And that’s not always the case when it comes to every lieutenant — including myself.”

Jones and Echo Company’s most senior noncommissioned officer, 1st Sgt. Paul G. Quesada, decided not to tell the unit about Hierl before her arrival. She would be treated like any other new officer.

Young enlisted Marines generally view new officers with skepticism and, sometimes, hostility. New lieutenants’ jobs as platoon leaders are peculiar: They have the most responsibility in the small units but often with less experience than the corporals and sergeants whom they lead.

Hierl, 24, grew up in Bethlehem, Pa., and worked on a horse farm in high school. Before graduating, she said, she knew little about the military, but opted for the Marines because, after meeting with a recruiter for the Corps, she thought that it “sounded good.”

“I wanted to do something important with my life,” she said. “I wanted to be part of a group of people that would be willing to die for each other.”

Her recruiter advised her to go to college first, steering her toward the Corps’ officer ranks.

In 2013, during Hierl’s sophomore year at the University of Southern California, Leon Panetta, then the defense secretary, announced that women would no longer be excluded from combat roles in the military. The moment remains a vivid memory because, Hierl said, it had not occurred to her that her gender could have kept her from leading Marines in war.

“I wanted to lead a platoon,” she said. “I didn’t think there was anything better in the Marine Corps I could do.”

Women make up about 15 percent of the military’s 1.3 million active-duty troops. Most jobs in the Air Force and in the Navy have long been open to women, except in special operations units, like the Navy SEALs.

The Marine Corps, which initially challenged the Pentagon’s 2013 order and was overruled, allowed women into its infantry ranks in 2015. There are 184,473 active-duty Marines, of whom 15,885 are women. Among them are 80 women serving in previously restricted combat roles.

Hierl has avoided publicity and is reluctant to talk about herself. But she did say that she wants to be seen by the Marines in her platoon as a leader, not as a trailblazer because of her gender.

Hierl’s arrival to 3rd Platoon was, as some put it, strange. Lance Cpl. Kai Segura, 20, is among the young Marines who make up a majority of 3rd Platoon. He was suspicious of Hierl until she led the group back from an exercise in the Mojave Desert.

Her seemingly casual pace turned out to be deceptively fast, forcing the other Marines into a near jog to keep up. And in the months that followed, Hierl earned 3rd Platoon’s quiet respect. With help from Staff Sgt. Jesse Rodriguez, the platoon’s top enlisted Marine, they found their footing. “She’s one of us,” Segura said.