use of artillery

[Zap]

Playing against the Ai in WWII campaign. My question is using artillery to soften troops in an advance. How many turns do I need to use my artillery to be effective.
It seems that I am moving in too soon with my mobile units. I have met with a lot of resistance.

[DROregon]

I use "early & often" as the rule for artillery. For offboard battery units, I start by turning off all but one gun. Shoot one at a time as each will suppress. I find the constant hits, even if small, will suppress the enemy to enable the mobile units to send the emeny fleeing. As instructed in the artillary tutorials, I then walk the artillary back as I advance my units. By the time I've used all / most artillary ammo, I've punched through.