The physical and psychological rigors of combat are intense, and militaries have the challenge preparing their soldiers for the worst of what they may face on the battlefield.
The world’s militaries require their personnel to go through gruelling training to equip them for life in the field, and to make sure that soldiers who might not have prior combat experience are still in a state of readiness.
Here are photos from around the world of some of the toughest training imaginable.
In mainland China, paramilitary policeman face an intense regimen. Here, the policeman take part in a training session in muddy water.
Training is sometimes aimed at pushing troops to their absolute limit: here, paramilitary police in China train at holding their breaths underwater.
A Canadian soldier in Latvia takes part in ice plunge training as part of NATO exercise Operation Atlantic Resolve.
US Marines also take part in annual joint drills with their counterparts in Thailand, in opposite climatic extremes. During the jungle survival exercises, Marines have the chance to drink cobra blood.
Here, a US soldier in the 10th Special Forces Group jump off the ramp of a Chinook helicopter with his military working dog during an exercise.
Over in Japan, members of the Ground Self-Defence Forces practice holding onto a rope dangling from a cargo helicopter.
In Taiwan, in order to pass the final stage of a nine-week Amphibious Training Program, a trainee crawls along a 150-foot path of jagged coral and rocks on his belly.
In Belarus, servicemen must pass through an extensive and difficult obstacle course before becoming members of the elite 'Red Berets.'
Militarize around the world make use of endurance challenges. In Israel, soldiers from the Golani Brigade must complete a 43-mile march to finish advanced training.
Enemy forces in the region have clearly taken note: In the Gaza Strip, Palestinian militants from the al-Aqsa Martyrs Brigades train in anti-Israel military drills.
Like the YPG, Iraq's Shiite militias are one of the major ground forces fighting ISIS. Here, members of a militia demonstrate close-quarter combat skills at a graduation ceremony.
Other Shiite militias in Iraq require their members to take part in desert field training exercises before graduation.
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