The window of opportunity for female volunteers to participate in the Marines' infantry officer course is rapidly closing.

Two female volunteers, both fresh from officer training, were unable to pass the first-day Combat Endurance Test on Jan 8, said Marine Corps spokeswoman Capt. Maureen Krebs. Fifteen male officers in the 118-member class also failed to pass the test.

This iteration of the course represented one of the last opportunities for female officers to pass the notoriously difficult program. To date, 26 female officers have attempted the course and not one has made it to graduation.

Krebs said the Marine Corps plans to wrap up its research into the integration of women into combat roles in June of this year. That means female Marines will have just one more opportunity to participate in an April iteration of IOC before the class is once again closed to women.

Likewise, the window for female Marines to participate in enlisted infantry training is also closing. Female volunteers are no longer being cycled through Infantry Training Battalion at Camp Geiger, North Carolina, though some seven MOS-specific ground combat training programs opened to female Marines in July. These include tracks for mortarman, machine gun, infantry assaultman, anti-tank missileman, M1A1 tank crewman, assault amphibious vehicle crewmember, and field artillery cannoneer.

Krebs said the ITB research had concluded with a total of 240 volunteers, and a passage rate of 44 percent.

When IOC closes to female volunteers in June, it's not clear if or when female officers might again have the opportunity to participate in the course. All military service chiefs, including the commandant, Gen. Joe Dunford, must make recommendations to the defense secretary of Defense by the end of 2015this year. The leaders se can include requests for exceptions to the policy that will open all closed fields to women in 2016.

Ongoing research efforts for the Marine Corps include the Ground Combat Element Integrated Task Force, which includes male and female volunteers working together in infantry and ground combat companies to assess existing training and readiness standards and develop gender-neutral standards for combat units. The task force is preparing for a February "deployment" to the West Coast, where its members will undergo a series of assessments. Krebs said GCEITF will continue its research until July.