For 70 years, women arriving at Marine Corps boot camp have learned to fire rifles, slide down ropes, and sprint through obstacle courses while separated from male counterparts. But now, for the first time, a platoon of women has been integrated into one of the all-male training groups.

The platoon of 50 women, training at Marine Recruit Depot Parris Island in South Carolina, will still perform most exercises apart from the men, but they will join together for larger training missions.

It’s a small step — and one that would be a step backward for other military branches — but is a notable advance in integration for the Marine Corps, which has the lowest percentage of women of any military branch and for years has resisted efforts to integrate its fighting forces.

The rest of the military is already completely integrated when it comes to basic training. In Army infantry training, for example, women and men have been tramping through the woods in mixed squads for nearly two years. But the Marines have said that too much mixing would distract recruits, and perhaps intimidate female Marines.