It is a rite of passage that I have experienced: brand-new lieutenants introducing themselves to their platoons of a few dozen enlisted Marines. It is a powerful experience for any new officer. Now consider the stakes when that lieutenant is a woman — and the platoon is a front-line infantry unit. The Marine Corps is the most male-dominated of the armed services, and the infantry is the most male-dominated bastion of the corps. The moment will be electric, and historic.

Soon enough it will also be a reality. On Monday, the Marine Corps graduated the first woman ever from its famously grueling Infantry Officer Course. (The Marine Corps has withheld the lieutenant’s name, at her request.) Of 36 women who have attempted the course since 2012, she is the sole finisher. I recall driving down Quantico roads and passing filthy, sweat-drenched former classmates from the Basic School (the gender-integrated, six-month course for new lieutenants from all parts of the corps) going through the Infantry Officer Course. They carried weapons and heavy packs, and one time, were red-faced and sputtering from being tear-gassed without masks. About a quarter of all applicants, almost all of them men, fail, 10 percent on the first day.

Infantry is the hallowed “tip of the spear” for the Marine Corps, among the first combatants into war zones. In keeping with the ethos of “every Marine a rifleman,” all Marines learn basic infantry skills, but only about 19 percent of the Corps is actually infantry; a few percent more encompass other combat arms specialties like artillery and armored vehicles. The rest of the corps supports them, whether through logistics, communications or gunfire from the air. Only since early 2016 have combat arms occupational specialties — including the infantry — been open to women. Women have made it into the infantry as enlisted Marines, but until now, none have become infantry officers.

Gender integration in the combat arms has been a source of much passionate debate within the military. About a year ago, the Pentagon released the results of a 2012 study by the think tank CNA that found that 76.5 percent of male Marines who have served in ground combat units were opposed to women in combat arms (56.4 percent of noncombat male Marines were, too). But this study was done at least three years before there were widespread integration efforts, including the corps’ Ground Combat Element Integrated Task Force, a unit created to study gender integration. None of the infantrymen had ever seen female Marines meeting the same physical standards as them. Now they have.