The face of the US Army has changed forever

"I totally support women in combat, women being eligible to compete for any position in the military," former Defense Secretary Robert Gates told Business Insider in an interview earlier this year.

"But I would agree with military leaders there can be no lowering of the standards of the requirements to perform specific jobs, lowering standards will put lives at risk," Gates added.

'Rangers Lead the Way'

The motto of the US Army's elite regiment could not be more fitting: "Rangers lead the way."

In April 2015, West Point graduates Griest and First Lt. Shaye Haver entered into the first gender-integrated Ranger School, alongside 380 men and 18 other female candidates.

Ranger candidates arrive for the 62-day training in the best shape of their lives and survive on a meal a day and just a few hours of sleep - all the while completing some of the toughest military training in the world.

"Ranger School is a gut check," Jack Murphy, a Special Operations 75th Ranger Regiment veteran and the managing editor of the military-focused publication SOFREP, told Business Insider.

"... When you see another soldier wearing a Ranger tab on his or her uniform you know that you have both slogged it out through some extremely challenging training, which automatically builds a certain amount of trust in each other," Murphy added.

Each year, approximately 4,000 students attend Ranger School.

Sixty percent of those candidates wash out of the course.

Welcome to Ranger School

The US Army divides the grueling course into three phases: "Benning," "mountain," and "Florida."

During the Benning phase of Ranger School, which takes place in Georgia, a soldier's physical stamina, mental toughness, and tactical skills are evaluated and fine-tuned.

On the last day of the Benning phase, Ranger candidates conduct an arduous 12-mile march while carrying a 35-pound ruck sack - and without the luxury of drinking water. About 50% of students will pass this phase of the course, according to the Ranger School website.

During the appropriately named mountain phase, Ranger students are sent to the northern Georgia mountains to continue to learn how to sustain themselves in adverse conditions.

"The rugged terrain, severe weather, hunger, mental and physical fatigue, and the emotional stress that the student encounters afford him the opportunity to gauge his own capabilities and limitations as well as that of his peers," according to the US Army.

The last phase consists of fast-paced field-training exercises in which candidates are evaluated based on their execution of high-stress raids, ambushes, and close-combat attacks.

All students must pass an intense physical fitness test that includes 49 push-ups, 59 sit-ups, a 5-mile run with a 40 minute time limit, six chin-ups, a timed swim test, a land-navigation test, several obstacle courses, three parachute jumps, four air assaults on helicopters, and 27 days of mock combat patrols.

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