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Crawling through a tiny tube.

US Army Reserve Spc. Alex Thompson crawls through a tube for confined space familiarization training during Combat Support Training Exercise at Fort McCoy on August 13, 2018.

Army firefighters train to rescue troops who are trapped in tight spaces.

Read more about the training here.

Dangling from a helicopter in the air.

Marines hang from an MH-60S Seahawk helicopter during Special Patrol Insertion and Extraction training underway in the South China Sea, Oct. 11, 2018.

Special Patrol Insertion and Extraction is a method to insert or recover troops from areas where helicopters and other planes can't land.

Getting kicked in the groin.

German combatives instructors train Maneuver Center of Excellence instructors on the new German army combatives course Sept. 12 through 28 at Kelley Hill at Fort Benning, Georgia.

The German army infantry combatives course is a new program at Fort Benning, where soldiers learn "

Jumping out of airplanes and opening the chutes at low altitudes.

A US Air Force Guardian Angel Team conduct a high altitude, low opening free fall jump working with a C-130J Super Hercules from Bagram Airfield, Afghanistan, March 23, 2018.

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They conduct high altitude, low opening jumps like this to

Read more about the training here.

Getting sprayed in the face with pepper spray.

Army Pvt. Antonio Martinez, a military police officer, is sprayed with oleoresin capsicum while conducting familiarization training at Joint Base Elmendorf-Richardson, Alaska, Oct. 9, 2018.

Floating in dirty water.

Cpl. Kevin E. Kusler floats through stagnant muddy water as he avoids concertina wire during the jungle endurance course June 20 at the Jungle Warfare Training Center on Camp Gonsalves, Marine Corps Base Camp Smedley D. Butler, Marine Corps Installations Pacific.

Jungle warfare training at Camp Gonsalves, where this picture was taken, provides Marines with experience in fighting in dense jungle environments.

Or wading through water under barbed wire.

A US Marine candidate navigates barbed wire through the Quigley Assault Course at the Officer Candidate School, Marine Corps Base Quantico, Va., Oct. 5, 2016.

Remaining still as a snake crawls over you.

A southern black racer snake slithers across the barrel of junior US Army National Guard sniper Pfc. William Snyder's rifle as he practices woodland stalking in a camouflaged ghillie suit, April 7, 2018, at Eglin Air Force Base.

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Getting choked while your fellow Marine executes a knife strike on your neck.

Lance Cpl. Dalton Swanbeck (top), a combat photographer with the 11th Marine Expeditionary Unit (MEU), executes a knife strike against Cpl. Adam Dublinske, a combat mass communicator with the 11th MEU, during martial arts training on Camp Pendleton, Calif., Sept. 28, 2018.