Infantry, artillery and tanks with "radio" icon

[jappleby]

I am trying to understand the different mechanics of some of the units but cannot figure out first what does the units with the radio icon signify and why do some of the units not fire on the enemy with clear line of sight. Wish there was a manual to assist with the different units

[chantodos]

radio can improve artillery accuracy if the target is within the radio zone

[DasaKamov]

Originally posted by jappleby:

Wish there was a manual to assist with the different units

There is. ;)
https://www.eugensystems.com/steel-division-2-game-manual/

(It's also linked to in the Pinned "FAQ" topic.)