Sneaksie, thanks again !
It's now clear that I didn't understood everything I saw in game.
I allways refused to let my tanks go forward to engage an ennemy it saw but couldn't fire at.
I'll sure try this, and specially observe if it comes back to previous position.
About SPG turning to face enemy, my remarks came from 2 observations.
First :
Please imagine a hill.
On southern side, my PzIV/70 oriented to east. No enemy in this direction, but I wanted to set an ambush this way.
On northern side of the hill, about 250 m from my tank, ennemy armored cars, light tanks and infantry. Note that my panzer couldn't see them.
With "don't move" assigned to my panzer, it stood looking at east, but simply refused to fire when another ennemy tank group came in my ambush zone, because none were exactly in front of him.
With it's freedom to move, my panzer left his place to engage the first ennemy group, and was instantely destroyed by flanking tank group.
Second situation :
Multiplayer game. A hill again.
I'm west with british armor. I have an archer*
Ennemy with german armor coming from east.
I gather my tanks in compact line to face ennemy.
My policy is to wait him to come, but archer goes to him.
I stop the archer and issue a "don't move" order.
When ennemy finally comes, the first that can be shooted is at 10 o'clock from the archer, but it doesn't turn... and would surely have died if my other tanks hadn't broke ennemy's gun.
Do you understang why I talked about SPG to be able to rotate when ordered not to move ?
BTW : why is the archer so slow in game ?
It's speed is set at 5 km/h, but I saw that it's cross-country speed was almost 12km/h (8mph).
sources :
http://www.wwiivehicles.com/unitedkingdom/tanks-destroyer/archer.asp
http://en.wikipedia.org/wiki/Archer