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 grueling 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 policemen take part in a training session in muddy water.
Later in the training, the paramilitary police also have to crawl under fire obstacles ...
... and hone their hand-to-hand combat skills.
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