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Flaws and gaps of samurai armour
🕑 Added 2022-09-26 11:00:08 +0000 UTCFor an armour with such complete protection, tōsei gusoku (当世具足) actually has surprising numbers of flaws and gaps. These weaknesses are well-known, even to the Japanese themselves, and samurai even developed specific swordfighting techniques known as kaisha kenjutsu (介者剣術, lit. 'Armoured swordsmanship') to exploit them. While many of these flaws are the result of careful design deliberation (i.e. some armour coverage are sacrificed for better cost-effectiveness, lighter weight, and better flexibility), others are easily solvable but left in place for no apparent reason.
Moreover, efforts to address these flaws appear to be patchwork in nature, as if Japanese armourers deliberately avoided making drastic alteration to the main harness. Not only this resulted in excessive numbers of auxiliary armour parts, but the solutions tend to be less reliable than direct improvement to the armour.
In this article, I'll explore some of the more obvious flaws and gaps of samurai armour, as well as their solutions.
Weakness 1: wrist and inner arm
Many samurai armguards, known as kote (籠手), leave the inner arm vulnerable. While this is not a flaw per se, but a deliberate design decision to cut down cost and weight (as similarly exposed design can also be found on armguards of other cultures, such as Chinese Bi Fu (臂縛) and munition-grade plate armour in Europe), the weakness is compounded on samurai as they rarely use shields or fought on horseback.
Solution: armguard with enhanced protection
While this problem can't be completely solved without seriously restricting arm movement, samurai willing to pay for it can opt for better-designed armguards that reduce vulnerable area as much as possible.
Weakness 2: back of the leg
As with armguards, samurai cuisses, known as haidate (佩楯), are wide and flat, only covering the front half of the thighs. Similarly, most samurai greaves, known as suneate (臑当), are half-greaves that only cover the shins.
Solution: armoured trousers and auxiliary calf splints
Since it isn't practical to create fully enclosed solid cuisses, samurai that wanted more protection for their lower limbs can wear armoured trousers such as kusaribakama (くさりばかま or 鎖袴) under their armour. For lower legs, a type of splint plates known as okubyō-gane (臆病金) or yoborogane (膕金) can be worn behind the greaves to protect exposed calves.
Weakness 3: free-hanging spaudlers
Samurai spaudlers, known as sode (袖), are free-hanging from the cuirass, a throwback to the large ōsode (大袖) pauldrons of earlier armour designs. Unfortunately, while this was a great feature on earlier armours, allowing the large, panel-like ōsode to be shifted around and function like shoulder-mounted shields, it is hugely problematic on the smaller spaudlers, as they inevitably flail around uncontrollably or even flip over during intense movement, exposing the poorly protected arms underneath.
Solution: armguard with integrated spaudler
A simple solution to this problem is to tie the spaudler to upper arm with a cord, although for some reason this wasn't widely practiced by the samurai. Alternatively, a type of improved armguard, known as bishamon kote (毘沙門籠手), directly integrates a spaudler into its construction to eliminate the problem altogether.
Weakness 4: armpit
Unprotected armpit is a weakness universal to all rigid and semi-rigid armours that can be fatally exploited, due to the fact that a thrust to this area can easily bypass the ribcage to puncture the vulnerable lungs and heart behind.
Solution: armpit protector and under-armour
While it isn't possible to completely seal off the armholes, armpit protectors known as wakibiki (脇曵) can be worn outside the cuirass to cover up the majority of the vulnerable area without restricting arm movement. Some samurai also wear under-armour known as manchira (満智羅) to protect their armpits, or use armguards with integrated voiders.
Weakness 5: significant gap between cuirass and tassets
Samurai tassets, known as kusazuri (草摺), are directly attached to dō (胴) cuirass through suspending cords known as yurugi-no-ito (揺糸). This creates a significant gap that, while visually obscured by uwa-obi (上帯) sash, actually leaves the vital abdomen of the samurai completely unprotected.
Solution: armoured belt 
There are many effective solutions to the abdomen gap problem such as shortening the suspending cords to narrow down or completely close the gap, replacing the relatively fragile cords with more protective materials such as chain mail or even metal plates, or covering the cords with small armour panels attached to the cuirass. Nevertheless, these solutions all require direct modification to the armour, and while a number of samurai armours do feature these improvements, a great many still don't.
Fortunately, samurai with unmodified harnesses can still opt for wearing an armoured belt such as kusari obi (鎖帯) over or under the suspending cords to protect their bellies.
Weakness 6: rigid and flared neck guard
Perhaps the most jarring flaw of Japanese armour, samurai neck guard, known as shikoro (錣), is rigid, relatively short, and flares away from the helmet. While this neck guard design appears to be intentional (Japanese armourers sometimes replace the aventail of captured Chinese or Korean helmet with shikoro), it creates a whole slew of problems for the otherwise well-protected head. Firstly, the flared shape creates unnecessary empty space under the helmet, which means a thrust from an angle may very well bypass the neck guard and pierce the neck, cheek, or ear of the samurai. Secondly, since the neck guard is short but rigid, it easily exposes the nape or side of the neck to enemy attack if the samurai so much as lowers or tilts his head, and careful upward thrust may slip under its lames to puncture the back or side of the skull.
Worse still, common auxiliary armours for the head, such as menpō (面頬) war mask and nodowa (喉輪) throat guard, offer little to no help to this problem.
Solution: enclosed armoured collar, secondary aventail, and collar of under-armour
Short of drastically redesigning the neck guard, there can be no effective solution to the flaw inherent to the design of shikoro. Thankfully some of the less common auxiliary armours, such as guruwa (曲輪), an enclosed and more protective version of throat guard, raised collar of manchira under-armour, as well as shitajikoro (下錣), a secondary mail aventail under the primary neck guard, can at least mitigate the flaw somewhat.
