The Marine Corps has been ordered to come up with a plan to make its enlisted entry-level training coed, and to make its job titles more gender-neutral following the recent move to open all military combat roles to women.

In a Jan. 1 memo to Marine Commandant Gen. Robert Neller, Navy Secretary Ray Mabus requested a "detailed plan" on how the service will fully integrate its boot camp and Officer Candidate School. The plan is due Jan. 15 and will be implemented by April 1, the memo states.

"The Department of the Navy's implementation plan must include gender integration of Marine Corps enlisted recruit training and officer candidate school," Mabus wrote. "In this submission, identify where, if anywhere, this training is already integrated, where it is separate, and specific steps that you will take to fully integrate these trainings."

In a second memo from Mabus to Neller on the same day, the SecNav directed the Marine Corps to conduct a full review of its military occupational specialty titles in an effort to ensure that they are gender neutral.

PARRIS ISLAND, SC - FEBRUARY 27: Female Marine recruits are disciplined with some unscheduled physical training in the sand pit outside their barracks during boot camp February 27, 2013 at MCRD Parris Island, South Carolina. Female enlisted Marines have gone through recruit training at the base since 1949. About 11 percent of female recruits who arrive at the boot camp fail to complete the training, which can be physically and mentally demanding. On January 24, 2013 Secretary of Defense Leon Panetta rescinded an order, which had been in place since 1994, that restricted women from being attached to ground combat units. About six percent of enlisted Marines are female. (Photo by Scott Olson/Getty Images)

Female Marine recruits are disciplined with some unscheduled physical training in the sand pit outside their barracks during boot camp at MCRD Parris Island, South Carolina. Marine officials have long touted the benefits of separate training for female recruits as it allows for intense mentoring between female drill instructors and the women in their charge.

Photo Credit: Scott/Olson/Getty Images

"As we achieve full integration of the force ... this is an opportunity to update the position titles and descriptions themselves to demonstrate through this language that women are included in these MOSs," Mabus wrote. "Please review the position titles throughout the Marine Corps and ensure that they are gender-integrated as well, removing 'man' from the titles and provide a report to me as soon as is practicable and no later than April 1, 2016."

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A Navy official said that the service received a similar memo pertaining to its MOS titles and descriptions. Mabus doesn't intend to require iconic titles like "infantryman," "rifleman" or "midshipman" to be changed, however, according to the official, who spoke on the condition of anonymity.

"The idea is not to go in there and change the name when 'man' is incorporated as part of the term," the official said. "... But when the word 'man' appears as a separate word ... they want that name to be changed."

Examples of some of those titles in the Marine Corps include reconnaissance man, fire support man and field artillery sensor support man. In those cases, the official said it's possible the "man" could just be dropped from the names.

Marine officials have confirmed receipt of both letters.

Lt. Col. Eric Dent, Neller's spokesman, said the Marine Corps is "working diligently to meet the intent of the Secretary of Defense's policy." The Marine Corps delivered its implementation plan to Mabus and Defense Secretary Ash Carter last month, Dent added, and it's now being reviewed by a Defense Department working group.

Each of the military services was required to present that plan by Jan. 1. The Army, Navy, Air Force and Marine Corps' plans were to include "timelines for integrating newly opened occupations and positions using their existing recruiting, accession, training, and assignment procedures," according to a Defense Department memo.

Since Mabus' memo on integrating boot camp wasn't sent until after that deadline, a Marine official said the Corps' plan didn't include details on changing its entry-level training. The official, who spoke on the condition of anonymity called Mabus' 15-day deadline to come up with a plan to integrate Marine boot camp "an aggressive timeframe."

"It requires a look at ... how much personnel to bring, how many drill instructors to bring, the leadership and support cadre that comes along with that," the Marine said. "The barracks in San Diego are H-shaped, for example, so you can see everything that's going on. If women are living in them, do you black out the windows or make an entire building that's theirs? Do you do a floor for men and a floor for women?"

150617-N-LV331-004 PABRADE, Lithuania (June 17, 2015) Secretary of the Navy (SECNAV) Ray Mabus holds an all-hands call with Marines participating in exercise Saber Strike 2015. Saber Strike is a U.S. Army-led multinational training exercise designed to facilitate cooperation amongst the U.S., Estonia, Latvia, Lithuania and Poland by improving joint operational capability in a range of missions. Mabus is visiting the region as part of a multinational trip to the U.S. European command area of responsibility to meet with military and civilian leaders and Sailors and Marines. (U.S. Navy photo by Mass Communication Specialist 2nd Class Armando Gonzales/Released)

Secretary of the Navy Ray Mabus holds an all-hands call with Marines participating in exercise Saber Strike 2015 in Lithuania in June. A Marine official called Mabus' 15-day deadline to come up with a plan to integrate Marine boot camp "an aggressive timeframe."

Photo Credit: MC2 Armando Gonzales/Navy

While male and female Marine officer candidates have trained together for years, the service remains the only military branch to segregate its enlisted trainees. Female recruits only attend Marine Corps Recruit Depot Parris Island, South Carolina, where they live and train separately from their male counterparts there.

Marine officials have long touted the benefits to this model as it allows for intense mentoring between female drill instructors and the women in their charge. But critics say it can backfire with female recruits not being held to the same physical standards as their male counterparts.

It's not immediately clear whether the Marine Corps' West Coast recruit depot could also open to women in coming months, but Mabus wrote that simply having Marines training on the same grounds won't cut it.

"Co-location does not meet the requirement for gender integrated training," he wrote.