Whenever a unit or an effect deals damage to one or more tiles or units, a damage step starts. Damage steps can be started either because of gunfire (direct attack, focused attack or attack of opportunity) or because of an indiscriminate damage effect such as shells or bombards, gas, or weather effects.
In case of gunfire, each attacker shoots once per figure (3 per figure for the gunner). Each shot deals 1 damage. Each body (units, buildings or trees and trenches) on the target tile has a certain number of hitpoints. If there are buildings or trees on the tile, this counts as a single extra body independent of the number of buildings or trees, with hitpoints equal to the total hitpoints of the trees or buildings. Each body has an equal chance of being hit. When the hit points of a body reaches 0, it dies. As buildings count as a single body, all hits on the buildings count as hits on the same building (if it has enough hitpoints). This means that dealing 3-5 damage against a city always destroys a single building, dealing 6-8 damage always destroys 2 etc.
If the target unit is in trenches, the trenches provide 3 additional bodies with 1 hitpoint each.
If there is another unit on the target tile that is being bypassed (such as a friendly unit when passing through them to attack) this unit also counts as a single body with hitpoints depending on the unit's hitpoints. If the target is bypassing another unit and the tile is a Trenches tile, then neither the Trenches nor the bypassed units provide any collateral bodies.
Any unit that is not fatally wounded after combat immediately regenerates hit points back to their maximum.
Explosives such as the sappers bombard ability or tanks shell ability deal damage in an indiscriminate step. For indiscriminate steps, each body has an equal probability of being hit. This means that on a tile with 3 militia, a zeppelin and 5 city buildings each body has a 1/9 chance of being hit.
Explosives deal 3 damage for each hit, and as such kill any unit or building. After each shot, the probabilities are recalculated.
If an explosive targets only a unit on an otherwise empty tile, the empty tile counts as a body itself. Since empty tiles cannot die, this means that there is always a chance to miss the unit. As hit probabilities are recalculated after each hit, there is no guarantee that your remaining shots will hit units if your first shots destroy all buildings or terrain on a tile.
Trample damage from tanks also counts as indiscriminate damage. Each tank body deals 1 damage to the tile that the tanks move onto. Since trample targets the tile specifically, units on the tile do not provide a body for this damage.
Gas and weather effects
Gas (from zeppelins or destroyed industry) and weather effects such as frostbite or firestorm also deal indiscriminate damage. Gas deals 3 hits of 1 damage, frostbite deals 2 hits of 1 damage and firestorm deals 3 hits of 1 damage.
However, gas and frostbite only target units. Firestorm also targets the tile itself, meaning trees, buildings and crops are at risk of death.
A body's hitpoints can be modified based on the space it is in; the body's hitpoints are reduced by 1 if the space is affected by Bonedrought or gas and the body does not belong to an air unit. If multiple modifiers apply, they all reduce the hitpoints by 1. Hitpoints are never reduced below 1.