The Combined Arms Penalty

[Green]

Just a couple more things that may or may not be obvious.

The penalty does not apply to attacks into a hex with Clear terrain. A Clear hex with fortifications, is still a Clear hex.

Whether or not an attack is supported is determined based on the combined support totaled across all attacking hexes. So an attack can be supported and yet may have tanks in a hex without any infantry. For example, a defender of 100 men is assaulted from a given hex by 120 men and 10 tanks and assaulted from another hex by 10 more tanks. Because the attack is supported, all twenty tanks are supported. 

And if an assault comprises only tanks, only tanks up to one tenth of men defending are unsupported. This follows from the formula since supporting infantry is zero in this case but some may have assumed that all tanks would automatically be unsupported. For example 20 tanks assault 50 men, then only 5 tanks would be unsupported.

Hopefully this is making things clearer...