What are the prerequisites for building new infantry corps?

[ulver1]

I have so far been unable to build any new land units apart from artillery – the option to build new units are grayed out. Oddly enough I can easily improve firepower but never build new units.

See screenshot

What am I missing?

[Chertio]

I think you need to choose one of the timer buttons to the left of the HMG symbol first, to decide how many turns it will take to build the new unit, and how much it will cost.

[Tamas]

I think you need to choose one of the timer buttons to the left of the HMG symbol first, to decide how many turns it will take to build the new unit, and how much it will cost.

Yes!

[ulver1]

Thanks – helped a lot.