It is a fundamental part of Marine Corps training. All Marine are trained for combat. Combat is a very chaotic place. It is very confusing and loud. While you can’t duplicate combat as a part of training the D.I. try to create a loud, confusing, chaotic place through yelling and “acting crazy”.

Why do all these things? Because it is the easiest way to get a human being who is unaccustomed to performance under stress to take action while being placed under an extreme and sudden stress environment (combat). It trains them to block out the noise and the fear and the stress and just do what they need to do. So the Omnidirectional Ass Chewing is one of the most important parts of onboarding. It is an act by these drill instructors to instill aggression and help them cope with combat stress without actually experiencing combat. These men aren't bullies. It is extremely important training, mental training. It is one of the most important things a Marine Corps Drill Instructor can do for a young recruit. The Yelling. In the Marines, boot camp instructors are actually trained on how to manipulate their voices so that they can yell for extremely long periods of time without damaging their vocal cords.

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