The two-and-a-half year period in which the Marine Corps' Infantry Officer Course became gender-integrated for research will end without a single female graduate .

The final iteration of IOC to accept female Marines on a volunteer basis began April 2 with two female participants. One was a volunteer and one was a member of the newly integrated ground intelligence track.

Both were dropped that same day during the grueling initial Combat Endurance Test, said Capt. Maureen Krebs, a spokeswoman for Headquarters Marine Corps. Nine of the 90 men who began the course were also cut.

IOC, held quarterly at Marine Corps Base Quantico, Virginia, began accepting female officers fresh out of training in September 2012 as part of a larger research effort into the feasibility of opening ground combat jobs to women. Lieutenants who made it through the legendarily tough 86-day course would not receive an infantry military occupational specialty or career advancement; they did it only for the challenge and the hope of being part of a historical Marine Corps achievement.

But as the research continued, few volunteers took advantage of the opportunity. By July 2014, only 20 female officers had attempted the course. Only one made it through the Combat Endurance Test, and none made it to the end.

In an effort to achieve their goal of 100 female volunteers cycling through IOC, the Marine Corps opened the course to female company-grade officers in October 2014, making hundreds more Marines eligible for the course. The Corps also began requiring that volunteers get a first-class score on the male version of the service's Physical Fitness Test in an effort to better prepare them for the rigors of IOC.

The effort was a mixed success. In the October iteration of IOC, three of the seven female volunteers made it through the Combat Endurance Test, bringing the total number of women to pass the test to four. Two of those who passed the test were captains from the fleet. As time passed, no influx of volunteers materialized, however.

The testing period ends with just 27 female volunteers having attempted the course. Two other female officers also attempted the course as part of required ground intelligence officer training. The 0203 ground intelligence officer military occupational specialty was opened to female officers in late 2013, with IOC as a qualification requirement for applicants. None of the 29 female officers made it to the end of the course.

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While IOC is closing to volunteers, female applicants for ground intelligence officer positions will continue to attend the course in the future, Krebs said.

Officials have said that ongoing research will consider many aspects of temporarily integrating IOC, including the number of volunteers, their pass rate, and performance in the course. That data will be taken alongside other research points, including the much higher success rate for enlisted female Marines in passing the Infantry Training Battalion course at Camp Lejeune, North Carolina. As of February, 358 women had attempted the course, with 122 graduates, for a pass rate of 34 percent.

Also considered will be data generated from the Ground Combat Element Integrated Task Force, which is conducting assessments with male and female troops in a variety of infantry specialties now on the West Coast. All this information will be compiled this summer and used to inform Commandant Gen. Joseph Dunford's recommendation to the secretary of Defense on whether or not to open remaining ground combat units to female troops.

A decision is expected from the Pentagon early next year.