Bayonets vs. Dedicated Melee Weapons

[Yanagi]

Well, a bayonet turns a long gun into something that can be used roughly like a spear both as a personal weapon but also a weapon to use while in close formation. That's good because it's a simple, multi-function weapon--shot, stab, club--for individual combat, but also can be used in mass ranks to charge and overrun the opponents line. Rifle-and-bayonet is a descendant of the pike square. In a setting you're describing where people are maybe having to jump rapidly from ranged to close combat, fixed bayonet (that doesn't block the barrel like a plug bayonet) would make sense if combined with training in how to as a group of infantry take on an opponent that's teleported in.

Or...it would work as entry level training for a modern recruitment-based army where the standard infantryman was bent towards mostly fighting other human-like armies but also need to melee with stranger opponents...but if the main opponents are demons that teleport (plus maybe other advantage like spells or jut being really big?) I suspect militarys would develop new tactics, and along with the new tactics would come new weapons. Sort of like how you have the basic pike square but then add on a doppelsoldner and a zweihander, or how a phalanx of hoplites would have peltasts or other chasseur-types on the flanks.

So if a battle is against demons that act like normal infantry or just like a stampede but there's also some teleporters...within each normal unit of there might be dedicated "watch for teleporters" soldiers who are armed and trained differently. Like...a couple of dudes with a scatter-gun and a big pig-sticker that are trained to watch the troupe's six.

But another possibility would be that demon-warfare would prompt the same kind of strategic hop that happened in just before and through WW1, with troops beginning operate in smaller teams and with different teams having different specialized equipment. So...anti-teleport troops might end up being a specialty unit carrying melee weapons best suited to rapidly engage and severely injure a demon or at least stop it from delivering whatever its first-strike option is.

And that's where the size and other advantages of the demons matter, because they effect the preferred weapon choice and corresponding the "drill" of how to deal with a teleport gambit. I generally think of demons as Large or bigger, so weapons suited to immediately thump something really hard but also with a but of reach to it, like a two-handed sword or a big heavy thing that can be swung.

ETA:

There's also a whole sidebar here to general strategy in demon combat, because presumably demons have abilities and magic that they deploy in a consistent manner because it's advantageous, and if they're organized or under command might even have their own formal doctrine. Depending on how many combatants have teleport and the exact rules of it's function, it would be a central component to demonic diesel-punkish warfare.

For example...teleport on a battlefield is effectively instant, effortless flanking, meaning the ability to select the very best position for enfilade and easy pincer movements. Depending on how rapidly teleport can be spammed, it also means rapid, low-risk feints and retreats as well as opening up commando-style targeting of critical assets...be that a decapitation strike or destroying critical material.

Anti-teleport doctrine would include anticipating likely points of attack and creating countermeasures. For example, having some light artillery training in on certain positions that are teleport-suitable, or secreting anti-teleport measures to be used advantageously to catch a demon(s) who's 'ported into an open position assuming they have a mode of immediate retreat.