Bogging down, and immobilization

[FragerZ]

I looked, but I couldn't find a thread on the 'tactics 101' section that referred to bogging down, and I needed answers so that I can make a good decision in a battle I'm currently playing.

So after a tank bogs down, under what circumstance will it unbog? Since almost every time I've seen a vehicle bog, it's become immobilized within moments.
(If a tank is in the process of bogging, I was curious on weather you could unbog it before it becomes immobilized, by pushing it with another tank.)

And most importantly, I need to know if vehicles are more likely to bog down if they are moving fast -- particularly in scattered trees.
If they do, then I'll order my troops to move through the trees. If there isn't much of an effect, I'll make them move fast -- and considering the battle these questions came from is a meeting engagement, time may be valuable. However, if a single tank bogs, it would be far worse then if they took an extra turn or two.

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P.S. Oh, and also, when a shell penetrates, does it typically explode? or will it only explode if it's labeled 'Large HE APBC'?

Secondly, if it doesn't explode, I assume that a tank is knocked out because of the fact that there's a shell bouncing around killing the crew and damaging the tank inside. If this is true, am I safe to assume that a vehicle is less likely to be knocked out of penetrated through the turret? (I'm particularly asking this question because I've noticed how the German tanks have comparable weak turrets, where the British and American tanks usually have strong turrets)

And finally, am I correct in saying that a tank can only push another tank if it's transport class greater than the other tanks?

Thanks for the answers, and perhaps you'll learn something from this post yourself.