1) Place in the editor tanks "T-100 Varsuk" or "MBT 52 Kuma" (where player is commander) You will see, that the default current weapon will be a heavy machine gun(MG), but not main Cannon!
2) Try switching weapon, between the current MG and main 125-mm cannon (default F-key) It will not work!
3) Then, change commander position to artilleryman position and you will see, that the weapon will changed automatically to the main 125-mm cannon!
This weird. If you go back again to the position of commander, only then, the current weapon will be saved as main 125-mm cannon. It's weird again.
Note! The AI-artilleryman will not be able to use main weapon until the player commander will not change position. (commander/gunner/again commander!)
For comparison, you can use M2A1 tank and you will see, that the default current weapon will be also MG, but switching weapons (by means F-key) will work initially and correctly.