Where else would you expect to find the greatest amount of lethal force possible but in the military; after all, it is in the job description for any member of the armed forces to be able to live and let die, and kill anyone that interferes with routine operations. The marines, in particular, have to be particularly skilled at getting in, inflicting harm, and getting out alive being the front of the line task force. As the relative bumper of the entire military, they need to be specially equipped, beyond the basic ability to fire a gun, to survive head-to-head combat. They are often considered either the bravest or craziest living specimens for their willingness to undertake such a risky task. The hope is to keep risk as minimal as possible by way of special military self-defense training.
Living with a rifle like its a prosthetic limb is the least intense part of a marines training. Being a body part primarily used for violent purposes, it is used as maximally as possible, both as a bullet-discharging object with extreme accuracy and as a blunt object with the same amount of accuracy. Part of the military self-defense training is strictly dedicated to letting a rifle be all the weapon it can be, as the single aide to a marine beyond his own raw might. Additionally, the marine learns other highly lethal martial arts styles to allow his own body become a self-defense vessel that can be intricately trained to bring swift death in times of desperation and minimal options.
This is only part of a universal tradition of military-based martial arts. Other countries have a variety of martial arts styles that were developed as a means to defend against invading forces. Muay Thai, for instance, came about in Thailand as the result of such a repeated history of invasion; this particularly exceptional example of worldly martial arts styles, sometimes referred to as the Art of Eight Limbs, has a technique called the Throwing Buffalo Punch which is capable of subduing a buffalo in a single strike. You dont want to get in the way of someone with this kind of training. The imagery created by such a powerful form of martial arts evokes the likeness of a Dragon Ball Z character, complete with fire-ball-blasting palms and legs that kick faster than the speed of optical perception.
Of course the described forms of military self-defense are just that: meant for military usage, not for scaring or beleaguering younger siblings. If any civilian plans on learning a form of military-based martial arts, the implications must be considered, being capable of wreaking early departure upon the recipient of any of the inclusive techniques. It would be most acceptable for use against armed aggressors and ones with cruel intensions; in such instances, power blasts would be deemed permissible as a fair means of retaliation. Irreversible pain should only be experienced by those that truly deserve it, and it takes a lot to deserve it.