With no notice and little formal explanation, the Marine Corps altered one of its notoriously grueling rites of passage late last year, changing the combat endurance test on the first day of its Infantry Officer Course from a pass/fail requirement to an unscored exercise.

Officials with Marine Corps Training and Education Command confirmed to Military.com on Friday that Commandant Gen. Robert Neller had made a decision in November to transform the test from a high-stakes hurdle to an assessment from which students can drop without risking their place in the course.

While officials said the test has had a historically low attrition rate since it was made a passing requirement in 2012, the change stands to have significant implications for women attempting the course. Of the more than 30 female officers who have attempted IOC, most have dropped during the combat endurance test on the first day.

Last September, a female second lieutenant made history when she became the first woman to pass the course and receive the 0302 military occupational specialty. The officer, who has not been publicly identified, passed the entirety of the course, including the CET, an official told Military.com.

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The change to the course was first reported by Marine Corps Times earlier this week. The secrecy with which the Marine Corps made the change is strange, considering the public debate surrounding the infantry officer course and the test as women have attempted it.

“[Neller] approved modifications to the IOC [program of instruction] to better tie student evaluation and graduation requirements to published infantry training and readiness manual, military occupational specialty specific performance standards, and operating force requirements,” TECOM officials said in a statement.

“As a result, the combat endurance test reverted back its original intent, prior to 2012, as an assessment tool to measure the retention of knowledge, skills and fitness achieved at the basic officer course,” they said.

Officials said performance on the CET would “inform” a student’s overall graduation evaluation moving forward.

TECOM officials said the data shows the overall attrition rate for the combat endurance test was not high. In the most recent iteration of the 86-day infantry officers course, which ran from September to December, less than one percent of the graduates would have failed the CET, they said. That rate, they added, was consistent with the annual CET attrition rate for 2017.

Anecdotally, however, the dropout rate for the CET has at times been much higher.

When a Christian Science Monitor reporter observed the test at Quantico, Virginia in October 2014, 30 Marines out of the 100 in the course dropped out on the first day. When The New York Times visited in July 2012, when IOC was opened to women on an experimental basis to gather data, 20 of the 96 officers dropped on the first day; seven voluntarily quit, seven were injured and six failed outright.

Marine 2nd Lt. Sage Santangelo wrote in a March 2014 opinion editorial in The Washington Post that when she attempted the course that year, 28 lieutenants, including the three other women also taking the course, had dropped along with her after the combat endurance test.

At the time Santangelo took the course, 14 women had attempted it. All but one had dropped during the combat endurance test -- and the one who passed the test ultimately had to drop the course due to stress fractures in her foot.

It’s not difficult to understand why the test has presented such a barrier to women. In addition to other physically and mentally challenging tasks, it requires Marines to hike miles with combat loads weighing 80 pounds or more and complete an obstacle course that includes scaling a 20-foot rope multiple times and getting over an eight-foot bar.

On average, female Marines, shorter and lighter than their male counterparts, are carrying a higher percentage of their body weight and stand a greater risk of injury as a result.

The extreme standards of the combat endurance test have sparked vigorous debate about whether it serves as an accurate evaluation of Marines’ leadership skills on combat or merely a kind of grueling initiation rite.

In 2014, retired Army Colonel Ellen Haring questioned the validity of the combat endurance test as a pass/fail requirement, saying it was not a good approximator of occupational requirements to be a Marine infantry officer.

She proposed then what the Marine Corps finally opted to do late last year: leave the combat endurance test in place, but eliminate its status as a washout point in IOC.

“Let’s call it what it is -- a challenging initiation into an elite group that prides itself on being tough, resilient and loyal to the foundational beliefs of this country,” she wrote in the online journal War on the Rocks. “And, let’s acknowledge that this initiation is central to the identity of the Corps, an identity that has been at the heart of its long and distinguished service to the country.”

Others have argued, however, that removing the pass/fail status of the CET would essentially be lowering the standards of the infantry officer course and leave women who pass the course but don’t complete the test vulnerable to criticism.

“Even if the CET is an initiation rite and not an indicator of how well a Marine will actually perform in combat, I am still leery of changing the actual test itself in lieu of women. This does signal the ‘lowering of standards,’” Georgetown graduate student Tessa Poppe wrote in Task and Purpose in 2014.

Marine 2nd Lt. Emma Stokien, a Marine Corps intelligence officer, also defended the combat endurance test in a 2014 opinion editorial in War on the Rocks.

“Changing this rite of passage will be doing female Marines no favors in trying to be infantry officers. Female Marines often have to work much harder than their peers to earn the same respect, and entering the infantry under the dark cloud of even perceived lowered standards will make this a practically impossible challenge and potentially cause real harm to unit cohesion and the faith between leader and led,” she wrote.

“I firmly believe that female Marines deserve to have the best opportunities and equal respect for the work we do, and I have high hopes for our changing role in combat and in the Corps,” she wrote.

TECOM officials disagreed with the assertion that the change represented any lowering of standards.

“The quality of the course, and the caliber of infantry officers it produces remains the same,” they told Military.com in a statement. “The Marine Corps continuously improves upon programs of instruction to reflect the requirements of the operating environment.”

Editor's Note: This story has been corrected to reflect that Marine officers carry 80-pound loads during the combat endurance test. At other points during the 86-day infantry officer course, they carry 152-pound loads.

— Hope Hodge Seck can be reached at hope.seck@military.com. Follow her on Twitter at @HopeSeck.