Vulnerability of Samurai Armor

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Vulnerability of Samurai Armor

Postby HanshiClayton » Fri Jan 23, 2009 12:21 pm

Reference, "Senjo Kumiuchi," battlefield grappling, and "Kumiuchi Kenden," wrestling over a sword, Serge Mol, Classical Fighting Arts of Japan: A Complete Guide to Koryu Jujutsu, Kodansha, 1970.
Also, "Koshiki-no-kata," in Hal Sharp's Classic Judo Katas, Rising Sun Productions, 2006.

One of the possibilities faced by the Shuri bodyguards (see Shotokan's Secret, Expanded Edition) was a bare-handed encounter with a samurai warrior dressed for battle. That means helmet and armor.

The art of fighting a soldier in armor is known as senjo kumiuchi (battlefield grappling), and kumiuchi kenden (wrestling over a sword). This type of fighting is the basis of all Japanese grappling arts, with a documented history going back at least to the 1600's. The armor deflects sword cuts, but it did not protect the wearer from hand-to-hand locking and striking techniques. The kumiuchi techniques are not usually practiced anymore, but you can glimpse them in judo's koshiki-no-kata, in which the performers step slowly and ponderously, pretending to be encumbered by their armor.

This is an illustration borrowed from It shows the typical sword cuts one would attempt against an armored opponent.


Samurai armor was all custom-made, so it is dangerous to generalize about design. In addition, surviving examples tend to be "best" examples, meaning the most costly, most complete, most ornate, or most famous. This "celebrity armor" is also heavier and more complete than that of the typical soldier. The king or general rode a horse into battle (so he didn't worry about weight), and enemy archers peppered him with arrows (so he covered up as thoroughly as possible). The armor of the rank-and-file soldier was far less grand, forming a patchwork of protection with gaps that the unarmed fighter could exploit.

Surviving examples of Japanese battlefield armor suggest that the following observations are valid:

  • The helmet was designed primarily to deflect downward-slashing sword cuts. It was held in place by a leather chin strap.
  • The face guard was worn like a Halloween mask. It could deflect a slashing blade, but offered no resistance to direct impact. The mask covered the face below the eyes, and extended down to shield the front of the throat.
  • Surprisingly, the side and back of the neck were often left bare, as were the top of the shoulders and the upper back above the level of the armpits. The kesa kiri, or monk's robe cut, takes advantage of this weakness. The sword enters at the base of the neck and cuts through to the opposite armpit, skirting the top edge of the breastplate.
  • The breastplate protects against a horizontal slash across the belly or lower back.
  • The skirt deflects downward-slashing attacks to the groin or thighs. There is no armor protecting the groin or thighs from below.
  • There is light armor on the forearms and shins. Sometimes you see light armor added over the shoulder joint, the top of the shoulders, or circling the base of the neck. Often these accessories are missing.
  • The armor is not hinged at the joints. The armor leaves gaps at the joints to allow movement.

As karate fighters, we can strike the side of the armored warrior's neck if we yank the helmet askew. We can strike the back of the neck or the upper spine if we force the warrior to bend over at the waist. A hard punch or knee-lift into the faceplate will do stunning damage. We can slip a blade under the edge of the helmet to reach the neck below the ear (carotid artery). A kick from below will travel up beneath the armored skirt and hit the groin.

All routine jujutsu joint attacks and throws are still viable. The armor does not protect the warrior's fingers, wrists, elbows, shoulders, knees, ankles or neck from joint locks. The weight of the armor slows him down and tires him. In fact, twisting the helmet like a steering wheel lends enough leverage to break his neck.

In all, the samurai in armor is a challenge, but not an insurmountable one. Once we take away his sword, the advantage is really ours.
Bruce D. Clayton, Ph.D.
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