BATTLE SUPPORT EXPLAINED:
See the visual aid at the bottom of the page.
Units engaged in battle automatically receive support from surrounding units. Units excluded from giving support are: special units like HQs and artillery (basically unit without combat strength), units without HPs, units behind river, units which were out of supply between turns, immobile units (like dugouts), units with more than 4 negative MPs, units in water while battle is on land. The extent of this support is calculated in the following manner:
1) First, each unit friendly to the attacker and adjacent to the hexagon in which the defender is located is marked to be giving attacking support.
2) Then, each unit friendly to the defender and adjacent to a unit giving attacking support nullifies one of the attacking supports.
3) After this, each unit friendly to the defender not employed in phase 2 to nullify attacking support and adjacent to the hexagon from which the attacker is attacking is marked to give defending support.
4) Finally, each unit friendly to the attacker not marked in phase 1 to give attacking support and adjacent to units giving defending support nullifies one defending support.
A diagram image showing this text explanation visually.
