Three women graduated from the Marine Corps enlisted infantry training course this week, a historic first for the 238-year-old service. But even though they met the same requirements as the men in their class, they won’t be assigned to infantry units for at least another two years while the Pentagon studies the effect of integrating women into combat roles.

Though the number of women serving in the armed forces has grown, allowing females to fight in combat has long been a contentious issue. Detractors say women don’t have the physical stamina to carry around heavy gear packs or haul an injured comrade out of harm's way. Women have mostly been relegated to support roles, the notable exception being female pilots who have been flying into battle since World War II.

The three women — Pfc. Julia Carroll, Pfc. Christina Fuentes Montenegro, and Pfc. Katie Gorz — proved that women can meet the same physical standards as men. The trio made it through the grueling, 59-day training regimen, which included a 12-mile hike during which they lugged around 85 pounds worth of equipment.

The distinction between combat and non-combat roles isn’t as important as it used to be. Warfare is becoming as much about sitting behind a computer as it is about dodging bullets on the battlefield. As technology advances, physical limitations will become less of an issue. And perhaps more importantly, the wars in Iraq and Afghanistan have already blurred the lines between who is fighting and who is not. More than 150 women have been killed between the two conflicts. Few, if any of them, were technically on the front line.

The role of women in the military has evolved over the last two centuries. During the Revolutionary and Civil Wars, women mostly served as nurses or cooks, though a few disguised themselves as men and fought alongside their compatriots. During World War II, more than 350,000 women put on a uniform and worked as secretaries, pilots, airplane mechanics, truck drivers, and radio operators. The end of the draft in 1973 opened up even more doors as military recruiters turned to women and minorities to fill the ranks.

By the 1990s, women had made tremendous strides. Thousands deployed during Operation Desert Storm. (Two were taken prisoner by the Iraqis.) They took command of an Intercontinental Ballistic Missile unit, a naval base, and an air-refueling unit for the first time. In 1998, a female fighter pilot became the first to launch missiles and laser-guided bombs in combat during Operation Desert Fox.

But certain career fields that involve the most hazardous duty — such as special operations, infantry, and artillery — remain off limits. These are often coveted jobs that help people gain promotions and move on to senior-level positions within the Defense Department. Military leaders say women will soon be allowed to move into those specialties, and they hope that the adjustment will even help cut down on the number of rape and sexual assault cases the armed forces see each year.

“I believe it’s because we’ve had separate classes of military personnel, at some level,” Marine General Martin Dempsey said in January, according to The New York Times. “Now, you know, it’s far more complicated than that, but when you have one part of the population that is designated as warriors and another part that’s designated as something else, I think that disparity begins to establish a psychology that in some cases led to that environment. I have to believe, the more we can treat people equally, the more likely they are to treat each other equally.”