DoD photo by Chief Petty Officer Ty Swartz, U.S. Navy

To be in the United States Marine Corps takes a person of extraordinary discipline, strength, resolve, and sense of purpose. Given how demanding the requirements are for even this baseline entry, getting through Marine Corps Reconnaissance Training must seem like an almost superhuman achievement to most civilians.

And for good reason.

Marine Corps Recon performs some of the most crucial — and dangerous — assignments within the military. Often the first boots to hit the ground ahead of other infantry forces, recon soldiers gather initial strategic intelligence for the Marines, providing an important window to evaluate local threats for future operations. Soldiers go through boot camp and the school of infantry, followed by Recon indoctrination and the Basic Reconnaissance Course (BRC). Advanced courses are also available to sniper, team leaders, parachutists and more.

WATCH: Surviving the Cut: Recon Marine Training (Video)

Nearly half of those who enter Recon training won’t see it through to the end. For those who do, those soldiers will have pushed their physical and mental limits near to their breaking points.

Here’s a look at the five most challenging training exercises these elite warrior endured along the way:

1. Swimming

These aren’t the same kinds of swimming courses you took in elementary school. Not even close.

Marines entering recon training are expected to be acclimated to wet environments. To test to see how well soldiers endure the water, from the very first day Marines are put through a grueling swim test that includes treading water without touching the bottom of the pool for thirty minutes or more. In the process, Marines are fully clothed and given weights and rifles in the pool that they must pass around as they continue to stay afloat. Following that, Marines must swim 30 yards underwater, never rising to the surface.

READ MORE: Think You Could Swim From Cuba To Florida When You’re 61?

In order to maintain safety during exercises, swim training is always done with the assistance of monitors, who look for signs of exhaustion and drowning if a Marine ever nears danger.

Endurance Training

Not every drill is meant to test the endurance of a Marine. There are, however, exercises meant to sap every last ounce of energy. Entire days can be turned into what are essentially biathlons from dawn to dusk mixing a combination of swimming, running, rowing and strength training through the use of weighted backpacks and entire boats.

Although these training regimens heavily tax the physical abilities of any Marine, they are also intended to test the mental fortitude and dedication of every man.

What’s known as “The Longest Day” is an infamous 18-hour endurance test and the most dangerous part of the entire 12-week training program. It includes a 2,000-yard swim with an 80-pound bag in tow as well as a team exercise involving distance running, rowing and swimming while carrying a watercraft.

U.S. Marine Corps photo by Gunnery Sgt. James H. Frank

Night-Time Training

Running into the surf with a weighted bag on your back for hours at a time is difficult enough during the day. Add the extra elements of fatigue and not being able to see and Marines are left with both a physically and psychological challenging exercise.

After a day of physical activity, night-time exercise, particularly combat simulations, can be all the more difficult given the mental stamina and focus required to pull through. Marines in training can be “attacked” by instructors wielding guns that fire loud blanks and tear gas — events that can occur repeatedly and spread out over several hours.

Sniper Skills

One of the most challenging courses in the USMC, the Scout Sniper Course takes an additional 42 days to complete.

Though less physically demanding than the BRC is some respects, sniper training rewards a different skill set than is attained in basic reconnaissance training. Hitting a target from a distance isn’t a simple matter of pointing at shooting. It requires quick calculations to account for wind speeds, elevation, movement and other variables that could affect accuracy.

In this course, Marines learn skills such as marksmanship, camoflage, stalking, and more.

READ MORE: Top 10 Snipers of All Time

Mountain Warfare Training

Mountain training courses, an advanced program beyond basic reconnaissance training, takes the same kind of physical and mental challenges from BRC, places them at a higher elevation. The air is thinner and the ground is colder. Mobility and visibility have both been reduced.

Swimming with a 80 pounds of supplies in tow might seem to bad after climbing a mountain with that same bag on your back.

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