Hey, I didn't know about these books, and I will definitely check these out! Thanks for sharing this! About the bayonet, what makes a good stabbing weapon is whether or not the tip of the sword is aligned in the same angle than the grip. Yataghans, Falcatas/Kopis, are all excellent stabbing weapons because the tip of the sword straightens out despide the overhaul shape of the blade, whichs emphasize slashing/hacking moves at first glance. The Kukri is NOT an efficient stabbing weapon at all for this reason, the tip on most design is shaped down, not aligned with the grip, making it poor at thrusting, but great for deep deep cuts similar to a thin bladed axe. Same goes the other way around for the gladius: most people consider it as a stabbing only weapon while it is as much as good at chopping (especially the hispaniensis or Mainz designs). The French Yataghan-Bayonet is the most obvious example: it admits a nice curve but then straightens out near the tip of the blade to align with the grip. Its design were adopted by most armies then, for more than half a century.

This design is efficient for multiple reasons. Having more reach in melee than the enemy was a constant fear in bayonet and rifle-length designs during the 19th century, as most melee action were broken BEFORE the actual clash, so the reach of the weapon and its psychological impact was of first importance. There the curvature allows the blade to be longer, giving more reach to the musket in melee, without the risk of coming within the bullet's trajectory.

Secondly a stabbing-slashing curved bayonet replaces both the socket bayonet (which was usually permanently attached) which had many flaws, and the hanger/short-sword (which is too many times disregarded by people but was a highly effective weapon if kept in good state). In close quarters like house-to-house fights during the 1870-1871 war, the yataghan bayonet, wielded as a short-sword, has proved deadly to the point the Germans feared nothing more than getting in melee with French soldiers in areas where a bayoneted rifle was too cumbersome to fence with. This dual purpose also adds an economical dimension: you only have to produce one weapon instead of a bayonet AND an infantry short-sword. Some armies retained a symbolic short-sword after adopting the Yataghan-bayonet, but most discarded it.

Finally, straight triangular bayonets get stuck within a body almost everytime or at least give a hard time recovering while your opponent is in most of the cases not out of combat after one stab, letting you highly vulnerable: it gets sometimes an awful lot of stabs to put a man on adrenaline out of combat, and it gets very ugly, hence the horror soldiers had for melee action. Thing is as I stated it, the bayonet was more of a psychological weapon and melees would end in a matter of seconds if the contact was made (the charged party would usually just give ground rather than sustaining a bayonet charge, or the charging party would either be shot to the last man before actually entering melee: this has been the case during the Battle of Cold Harbor, 1864, for instance. A knife/sword shaped bayonet gives more workaround to the soldier to avoid being vulnerable after the first stab, and prevented the blade from getting stuck (as much as a sword though). A thrust with an actual flat blade also increases the chance of the wound to be lethal or incapacitating, cutting tendons or arteries, slashing to the face to make the blood blind the opponent and then finish him safetly, or whatever... You got the point!