Quote Originally Posted by The Grand Inquisitor
Armour protects vs missiles. Defence vs melee. They do not add together, though 'armour bonuses' are added to both armour and defence.
Ludens is correct, every point of armour gives a +1 defence bonus. This is the effect of armour. Every unit has a standard 1 point of base armour to start with, so I am not sure when the bonus vs armoured troops come into effect. All this bonus does is give the attacker +1 attack when he encounters "armoured" troops. The "missiles good vs armour" is also a bonus vs an armoured opponent, though, again, I'm not sure when an opponent is considered armoured? I would guess 2, as that is the result of the first level armour upgrade to a unit that starts with the base level 1 armour (unarmoured).