Yoroidoshi Tanto - Small but powerful an understated blade designed to breach armor

What is Yoroi-dōshi Tanto 鎧通?

"Yoroidōshi", literally translated to Armour Piercer, is a type of short katana, a tantō. It also known as "Metesashi" 馬手差し. Tanto was used as an auxiliary weapon when samurai fought with full armor on, and Yoroidōshi has a more specific purpose, is to stab into the gaps of the armor. 

Antique Yoroidoshi is rare, but they are widely recognized and popular as hidden weapons (anki) used for assassination in fictional stories, including anime, manga, and video games. This article will introduce the basics of yoroidōshi, the history and how it was used, and hopefully it will give you inspiration for your own custom tanto.

How long is a Yoroidoshi?

Typically, Yoroidoshi length varied from about 21.2 cm (approximately 8.3 inches or 7 sun) to less than 28.8 cm (about 11.3 inches or 9 sun 5 bu), with some even shorter versions existing. This shorter length, often not exceeding the distance from the hand to the elbow, was strategic, allowing the wielder to use it effectively in close combat and to maintain control when striking at the gaps in an opponent's armor.

The blade's construction near the hilt was notably thick and sturdy, a feature that enhanced its durability and strength. This thickness near the tsuka, known as kasane, contributed to the Yoroidoshi's resilience, enabling it to withstand the stress of penetrating tough samurai armor. The absence of a tsuba (handguard) on the Yoroidoshi is another characteristic feature, emphasizing its function as a tool for thrusting rather than for slashing.

Yoroidoshi Koshirae (Fitting)

Most of the existing Yoroidoshi saya are similar to those of typical tanto, known as Aikuchi-koshirae (合口拵), which means they don't have a Tsuba (鍔, handguard).

Designed to be worn on the right hip and drawn with the right hand, the Yoroidoshi's saya has unique features. The Kurigata (栗形, the knob through which the Sageo, さげお, the cord that ties the scabbard to the belt, is passed) and the Kaerizuno (返角, a fixture used to hook the scabbard to the belt to prevent it from being pulled out) are placed on the outer side, which would be the 'back' for a regular katana. The Kaerizuno is oriented towards the Kojiri (the end tip of the saya), which is opposite to the usual direction.

This reverse orientation of the Kaerizuno is a clever design to prevent the saya from being drawn out along with the blade when pulling out the Yoroidoshi with one hand. To prevent the saya from slipping off, the Sageo is either wrapped around the Kaerizuno or passed through a hole called "Inu-maneki" near the Kojiri, ensuring the saya stays in place.

History of Yoroidoshi

The Yoroidoshi evolved during the late Kamakura period (14th century) as close combat and grappling became more common in battles. This led to a preference for shorter, straighter blades with thick spines, crafted specifically for stabbing through armor. The Yoroidoshi originated from the Sasuga (刺刀), a type of stabbing sword. As the Sasuga evolved, it lost its curve and gained a thicker spine, leading to the form known as Yoroidoshi. 

How Yoroidoshi was used? 

Unlike Uchigatana, Tachi that were worn in the left,  Yoroidoshi was worn on the right hip in a reverse position, allowing for quick and easy access in the heat of battle.

In the late stages of Japan's Sengoku period, even ordinary infantry, known as Ashigaru, were often equipped with body armors called Doumaru and Haramaki, shielding the torso and thighs. Although not all of them wore iron armor, it was popular enough. Samurai warriors, on the other hand, wore even more refined and robust armor for enhanced protection. During this era, many high ranking samurai started using Nanban Dou, a type of European-style chest armor, known for its superior defense. 

Given the effectiveness of these samurai armors, traditional Japanese swords like the Tachi and Uchigatana were often ineffective in combat. A practice called Ikkiuchi (一騎討), popular since the Kamakura period, involved high-ranking samurai dueling in front of their troops, with foot soldiers cheering them on.

These heavily armored samurai, mainly using yumi or yari, often difficult to cause significant damage on each other despite numerous strikes. This led to a shift towards close combat and wrestling, techniques influenced by Chinese martial arts, evolving into the modern art of Judo.

The Yoroidoshi tanto, a type of dagger, was particularly useful after subduing an enemy with wrestling. Even the thickest armor had weak points, like the underarm area or the eyes, which were unprotected by their samurai armor.

If your enemy want to show you mercy, they will use the Yoroidoshi to threaten these vulnerabilities, often leading to a victory declaration without actually harming the opponent. For soldiers who were less skilled and less well-equipped than samurai, the strategy against heavily armored warriors was to pin him down in the ground, then use the Yoroidoshi to target the gaps in their armor.

This approach wasn't exclusive to Japan. In Europe, during the full plate armor era, soldiers also used short swords or daggers to target vulnerable areas after pinning down an enemy.

Moreover, the Yoroidoshi's shorter and robust blade made it less likely to break and was typically thicker and heavier than those of larger swords. In extreme situations, a powerful thrust could potentially penetrate armor. However, without a handguard (tsuka), there was a risk of injuring the user's own fingers. To effectively use the Yoroidoshi against armor, it required both hands: one hand gripping the handle in reverse, the other at the handle's end, leveraging the user's full strength and momentum for close-range thrusts.

Another use of Yoroidoshi, is when attacking a castle, its robustness was utilized to insert it between the stone walls and use it as a step. It's said that when the yoroidōshi was worn at the waist, unlike a regular sword, the handle was positioned at the back, and the end of the scabbard at the front, to prevent the blade from slipping out naturally during a grapple or being stolen by the opponent. This can be seen in paintings depicting Sengoku-era warlord Hosokawa Sumimoto.

Famous Yoroidoshi

The famous Yoroidoshi short sword known as "Tanto Mei Yoshimitsu" is also called "Atsushitoshirou" (厚藤四郎). It is listed in the "Kyoho Meibutsu Cho," a catalog of famous swords. This particular sword, made by the swordsmith Fujishiro Yoshimitsu, is a classic example of Yoroidoshi with an exceptionally thick spine.