A really good sword

[Tomsdad]

I was also a long time believer is the "differential hardening caused curved katana blades" theory but it was then pointed out that earlier Japanese straight single edged blades were also differentially hardened. So the smiths obviously knew how to produce other blade shapes with differential hardening, suggesting it was a choice. Certainly they could have compensated for the effect if they had wanted to. EDIT: On top of this as DanHoward points out not every Katana with the stereotypical curve were differentially hardened


The argument for benefits of a curved blade that I tend to agree with are:

1). Certain cutting actions against bare flesh (not every target was armoured and not every blow in combat had to get around armour).

2), Being on a horse and staying mobile favours certain attacks where having a curve helps*

2). Edge alignment when hitting being helped by a curve


These three kind of combine. i.e. if you are on a horse and riding through fleeing poorly equipped foot troops and have very short windows of opportunity and having to worry about staying in your saddle.



But two big points when it comes to samurai & katana's etc

1). it was never the samurai's primary weapon either when on foot or horse back. Although yes you still want your back up weapon to be as effective as it can be in the most likely situations you fight in case you do need it. But non combat factors can become more relevent than they'd otherwise be.

2). Generally** it wasn't that curved when compered to other curved blades (and curved blades used from horse back)

Originally Posted by Jinumon

I knew these guys were wearing helmets for some reason XD

Jinumon

Heh quite, armour was generally some combination of expensive, difficult and time consuming to make. Even more so when you put it in the context of equipping troops that you want to deploy. And yet despite that and it coexisting with weapons for thousands of years it never went out of style so I think it is safe to assume it did it's job against weapons enough to keep around.

Even when guns improved past the ability of armour to be effective against them in terms of efficiently deploying troops with it, it didn't actually take that long*** for advances in armour to make it competitive again.





*Although it's not 100% one way, there was big debate in the C19th regarding straight'n'stabby or curved'n'slicey for horseback (albeit it was being discussed in the C19th context). Debate finishing just in time for WW1!


**there's a range in the historical record because "katana" is actually a pretty general term, and it has covered lots swords for a long time


***in terms of the history of armour wearing anyway!