[Griefbringer]

One effect of stacking multiple units in same hex is that it slows down movement (as there is an additional cost for moving to a hex with units already in it).

As for shooting, it tends to be quite bad news for soft skin vehicles and infantry, as HE fire tends to have some effect (at least suppression) on all units in the target hex.

Armoured targets tend to be on the safer side, as AP fire tends to affect only the target unit, while light HE fire tends to cause the target little more than buttoning up. Very large calibre HE fire can however damage armoured targets even in neighbouring hexes.

Any infantry on the same hex as an armoured vehicle (or even worse, doing tank riding on it) will of course be negatively affected by even small arms fire targeted at the tank (the game does not provide opportunity of infantry taking cover behind a tank, like you might see in some Vietnam movies). Historically, infantrymen were not always fond of being in very close proximity to tanks, as they considered them attracting fire (as they tend to do in the game), not to mention the prospects of getting run over by one.

Tactics-wise, keep in mind that you can sometimes force enemy infantry units to retreat to hexes occupied by other infantry units. Especially handy if you manage to ambush an enemy infantry column advancing along a road - once you have suppressed them enough to eliminate return fire, start pounding at the first unit in column until it retreats to the hex behind with another unit in it.