Quick Guide to Combined Arms - The Holy Trinity Edit
Infantry + Armor + Artillery + Air Support = +75% CA Bonus
Infantry + Armor + Air Support = +50% CA Bonus
Infantry + Armor + Artillery = +50% CA Bonus
Infantry + Armor = +25% CA Bonus
Infantry + Artillery = 0% CA Bonus
Armor + Artillery = 0% CA Bonus
Minimum Armor Rule Edit
At least 10% of the force or 6 strength points must be armor to benefit from the armor bonus of combined arms.
Battlegroups are a great way to insure Combined Arms in any offensive or defensive situation. Consider creating battlegroups that combine units of armor, motorized infantry and motorized or self propelled artillery for use in hasty assaults. This will insure that your forces have a +50% CA bonus in any combat they are involved in so long as their artillery is still alive.
The Reserve order is also a great way to insure combined arms, consider placing an armor formation one hex behind the front lines with a Reserve order so that it can provide its armor value for combined arms to multiple friendly hexes both offensively and defensively.
Fire Missions can be used to provide the artillery value to all combat situations EXCEPT Hasty Assaults - which cannot benefit from fire support.