The common way to play with Low Luck is like this…
For every combat round you add the values of the attacking and defending units. For instance if you are attacking with 4 inf and 1 fighter and the defender has 2 inf, then the attacker has 7 attack points while the defender has 4. Every 6 points means that you’ll get a hit, and you roll a dice for the leftovers. On this case the attacker would have 1 automatic hit, while rolling a die and hitting with a 1, while the defender would roll a die to hit on a 4 or less.
Imagine both the attacker and defender had 1 hit each. On the next combat round the attacker doesn’t have to roll (it has 6) while the defender rolls for 2 or less. And it goes on until one or both sides are destroyed or the attacker retreats.
The same applies for ships doing land bombardment during amphibious assaults. With AA shots you can either roll individually for each plane, or you can roll for each type of plane.