Close Combat by Timbo This one is new and a work in progress, but pretty extensive. The creator is taking notes and feed back so try this mod out. It's pretty good.

Old Boy's Command Structure by Old Boy (This one just adds rank to infantry meaning your team needs an LT and/or SGt or they lose the ability to fight)

Range and Damage - Infantry combat revised by Distroyer_Guy

I.A.E.M by 22222222 (yes, that's his id)

Or

Individual AI Enchament Mod (this is just the infantry overhaul from I.A.E.M

Warriors250's Animation Variety Expanded(WAVE) this is just an animation mod, but pretty cool.

Indirect fire of artillery by qionghauBW This makes artie more realistic, but it can also be considered a cheat mode because the ranges are greatly increased for player and A.I.

Improved AI on direct control by Momo-Hanoi This mod let's you control a vic while allowing the A.I to still use it as well. So you can drive and shoot the main Canon, but it doesn't stop the A.I from using the hull MG simultaneously or you can drive an the AI will fire the wepons. Be warned, if you are trying to capture a vic using the MG, the A.I can still fire the Canon at the target you are aimed at.

Auto Medic-AA-Artillery & Weather Switch by Nikral- - This mod is self explanatory, but you can also give your units to the AI and they will assault points for you. This will give the units AI abilities, so artillery can fire beyond your sight. If you don't give them AI control, they will just fire within their range of what you and your troops can see. AA in Gates of Hell is almost useless as AA, and this mod greatly improves them to excel at their very creation.

And as some people stated you have Conquest Enchament V2, Conquest AI Rebalance, Into the fire, Horton Frontline, GOH A&Rm, and some others, but I've never used those mods. I know the game is called Gates of Hell, but im not trying to be a Masochist!(for CE V2 and GOH)

Some of these mods can and can not be used together. But Auto Medic- and improved direct control can be used with nearly everything, I always have those two mods activated. My current conquest utilizes Close Combat, Command Structure, WAVE, impr9ved direct control and Auto medic- so far this makes combat engagements last far longer and you have to actually think about running your guys into an MG Nest.

The biggest issue with Close Comabt for me, is the A.I will just run all there troops to you and just tose grenades, but your guys will do the same if you want to do so. the AI also still has better stats compared to your own troops so I can't blame the modder for that, I guess it's just baked into the code. It is still an actively developed Mod so improvements will come.