O-yoroi, or Great armour, was an early type of loose fitting, box shaped samurai armour appearing in use primarily from the 10th to the 12th Centuries.
The O-yoroi weighed about 30 kilograms, being made mostly from Kozane, scales of lacquered steel laced with silk, cotton or hemp braiding. To lessen the weight, lacquered scales of raw leather were either interspersed with the iron scales, or covered the less important sections.
O-Yoroi took around 9 months to complete, and used as many as 2,000 kozane scales. They were expensive and time consuming items, and consisted of six main pieces, being the Kabuto, or helmet, and the Menpo, or mask,…an apron like set of plates to protect the upper legs called a Haidate,…the Dou (body armour), Kote, being armoured sleeves, and the Suneate shin guards. Other pieces included the O-sode, large, rectangular shoulder guards. Early examples show the scales were often bound and then lacquered, while later pieces were individually lacquered before lacing to provide greater flexibility. The helmets were bowl shaped crowns made of multiple triangular pieces of steel, hammered into shape, and riveted together with large protruding headed rivets. They featured the distinctive swept back ear-like wings known as Fukigaeshi, which are said to have been to deflect arrows and protect the face.
While most samurai armour was not uniform as such, and ordered to the tastes and affordability of the samurai themselves, early O-yoroi lacing styles and colours indicated the ranks and clans of the wearer. Higher ranked samurai had tightly laced armour, while lesser-ranked samurai had loosely laced protection. Later, when loosely laced armour became the preferred style, rank was designated by the colors of the Nodowa, throat protector lacing. Interestingly, very few examples of the much preferred red silk lacing have survived, as the red dye used would hasten the deterioration of the silk in the sunlight, whereas the dark indigo and black dyes seem to have helped preserve the silk better.
Heavily laced armour was later shunned in favour of lesser lacing, as it reduced construction time and costs, decreased weight, allowed for greater ventilation, was not as heavy when wet, nor as difficult to clean of mud and blood. In some cases, sheets of printed deer skin covered the scales to further protects against rust and corrosion.
O-Yoroi were mainly designed with horse mounted archers in mind. The armour was heavy, bulky, less flexible than later models, and therefore more difficult to fight in. When mounted, much of the weight of the box shaped Dou was born on the saddle.
Once dressed in under-robes and hakama, the left, then the right Suneate were first fitted, then (from the Kamakura period) the Haidate is tied around the waist. Next, the left, then, if it is worn at all, the right kote is fitted. The right side of the “U” shaped Dou was open, and so the Waidate, a steel or leather plate with rows of scales hanging below it, part of the upper leg protection called the kusazuri were attached to this plate. This was tied to the right side of the body before the Dou was fitted and tied shut, encompassing the body. Like the Waidate, the rest of the Dou featured three sets of laced scales in rows hanging below the main body armour.
Towards the end of the Heian Period, the difficult to wear O-yoroi developed into the more convenient, easy to wear and more battle ready Do-Maru Yoroi.