This week, the Marine Corps publicly acknowledged a first in its history: First Lieutenant Marina A. Hierl is leading an infantry platoon. She is the first woman to do so in Marine Corps history, a ground-breaking achievement for a military branch that once forcefully opposed allowing women in combat. Hierl is only one of two women to pass the Corps’ rigorous combat evaluations course (37 women have attended), and the first to lead a platoon. In an interview with a New York Times reporter embedded with her unit in Australia, Hierl reflected about her role matter of factly: “I wanted to lead a platoon. . . . I didn’t think there was anything better in the Marine Corps I could do.’’ And so she did, building on decades of achievements of women in the military.

Five years ago, then-Secretary of Defense Leon Panetta announced that women in the military would be allowed to formally serve in combat, ending what had been known as the “combat exclusion rule,’’ which permitted women to serve in the active military but kept them from direct combat roles. It was not entirely clear, however, how the demise of the combat exclusion rule would actually fare in practice. The military has 1.3 million active troops, and only 15 percent of them are women. Women still need to satisfy the rigorous physical and mental demands of combat training. Today, the Marine Corps has only 80 women in previously combat-excluded roles. The Army has fared better, with 740 women now in jobs they once were not allowed to hold. It is a slow process.

But a process nonetheless. Hierl’s historic role is one moment in a long journey toward equal status for women in the military. It was a recognition that the Pentagon’s antiquated notions of whether females could in fact serve fully had finally been put to rest. The military spent years trying to justify why women should continue to be treated as second-class citizens. But the nature of the wars in Iraq and Afghanistan exposed a different reality: Women were already in combat in everything but name, leading to over 120 female deaths in those wars. The Pentagon’s new stance was less about shifting policy than finally acknowledging what was already occurring .

While the women of the ongoing Iraq and Afghan wars are given much credit for pushing the Pentagon to open its doors, Hierl’s achievements are also the result of the long-forgotten role of women in the first Gulf War. The first Gulf War was a watershed moment for women in the military and began the long conversation that ended with the demise of the combat exclusion rule. During the Persian Gulf War in 1991, 40,000 servicewomen went to war, and one of every five women in uniform was deployed in direct support of the combat efforts. Thirteen US servicewomen were killed there.

To understand how these women could be deployed to war, even die there, and not be “in combat’’ took a certain amount of verbal jujitsu and tactical blinders. The military simply pushed women into roles that put them squarely in harm’s way, but continued to insist they were not in combat but only in support functions. So flying a medical helicopter to pick up injured combat troops may have exposed women to harm, but they were not “in combat.’’

After the war, in 1993, then-Defense Secretary Les Aspin ordered the military services to allow women to fly in combat aircraft and seek places for women on most Navy combat ships. This shift to promote female aviators was a reflection that aviation — demanding, but not akin to the physical demands of combat training required in the Marines or Army — had long been welcoming to women. For example, hero Southwest Airlines pilot Tammie Jo Shults, who safely landed her aircraft after engine failure caused a hole in the plane’s body, was one of the Navy’s first trained female fighter pilots. Eventually, Shults bumped up against the combat ceiling and left the Navy just weeks before Aspin’s rule change.

Today, 15 years after that first change to combat rules for women, Hierl is a trailblazer but also, like the women before her, not the end of the story. At the pace of female integration, in one or two generations, women will qualify to serve as more than just platoon leader in the Marines.

A female chairman of the joint chiefs? It is, now, not inconceivable.

Juliette Kayyem was a columnist for the Boston Globe, where her series on the combat exclusion rule was a finalist for the 2013 Pulitzer Prize. She is on the faculty of Harvard’s Kennedy School of Government and the CEO of Zemcar.