Women and combat: Cracking the last all-male bastion in U.S. military?

The Marine Corps is under orders to open up its ground combat units - one of the last all-male bastions in the military -- to women, but it has been unable to find any female capable of making it through its three-month infantry officer course. 60 Minutes gets an inside look at the brutal training for a story that examines how the Marines are dealing with the order to open their infantry units to women. The story will be broadcast on 60 Minutes Sunday, March 15 at 7 p.m. ET/PT.

Beginning in September 2012, 26 women have attempted the course and all of them have been forced to drop out -- most on the first day. Despite that zero percent success rate, Brigadier General George Smith, the officer in charge of the program, tells David Martin the Marine Infantry Officer Course "is designed just right" and there are no plans to change it. "The realities of combat aren't going to change based on gender," Smith says. "The enemy doesn't care whether you're a male or female."

The course begins with a Combat Endurance Test, a series of physical and mental challenges spread out over 16 miles. The Marines - both men and women -- never know what's coming next or how long they have to complete the test. 60 Minutes cameras follow 2nd Lt. Melissa Cooling as she sets out before dawn, carrying a 30-lb. pack and rifle. Fourteen hours later 20 men have dropped out. So have all five women who started the day, including Cooling, who was defeated by a 25-foot rope climb.

Although no women have passed the officer course, 122 have made it through the less demanding enlisted infantry training, a success rate of 34 percent. But Pvt. Nisa Jovell, who passed with flying colors, tells Martin that women are not meant for the infantry. "We are not built for it, and I'm not saying we can't do it, what [men] do, but our body structure is different." Jovell says women's hips make it more difficult for them to carry the heavy loads required for combat. "The hip problem is definitely a big deal."

In combat, Marines are frequently required to carry a pack that, according to Brig. Gen. Smith, "very likely exceeds 100 lbs., and probably gets up above 130 lbs. in some cases." That's more than Cooling weighs.