Although all decisions during a battle come from the COs, the actual fighting in the Advance Wars takes place between different Units. Different Units have their own strengths and weaknesses. All Units normally start on 10 HP. A Unit can lose HP each time it is attacked or attacks (Depending on whether or not the defending Unit can retaliate). Once a Unit reaches 0 HP it is destroyed and removed from the battle.
There are several ways how players can obtain Units. On some Maps the may they may be already placed, they may arrive at a certain point during the battle (Though that's to do with Campaign) or they can be made. The only way for the player to make a Unit is br producing one at the relative building:
- Base: Produces Land Units.
- Port: Produces Naval Units.
- Airport: Produces Air Units.
- Carrier: Though not a building, Carriers in Days of Ruin may produce Seaplanes.
Producing a Unit costs the player a certain amount of War Funds (See the relative Unit pages for information on each Units cost).
Units movement over terrain is affected by their number of movement points and their movement type. Moving over each square costs a certain number of these points, but different types have different amounts required; for example, tires have a movement cost of 2 on plains, while all other units have a movement cost of 1, meaning that tire units move only half as far on plains. The weather and CO Powers can also effect movement costs and movement points. Units may not move onto another unit's square (except for special conditions), and cannot move over enemy units.
All Units have a certain amount of Fuel (Or Rations for Infantry and Mechs), once a Unit runs out of Fuel then it either becomes motionless (In the case of Vehicles and Infantry) or is destroyed (In the case of Naval Units and Air Units). Fuel can be restored to a Unit by remaining on their relative building or by having it restored by a APC or Black Boat. Units use one fuel per movement point used, and naval and air units use a certain sum every day.
Primary and Secondary Fire
Units may have up to two weapons, a primary one and a secondary one. If a unit can fire with the primary weapon, it uses that, but if not it uses its secondary weapon. Primary weapons fire is usually stronger, but this is not always the case; primary fire is also limited by ammunition. One unit of ammunition is used per attack (or defense) where the primary weapon is used, and if the ammo is exhausted, the unit can no longer fire.
In some cases, units can use special commands. Many commands are specific to a few units, but all units can join and most can load. Joining occurs when one unit moves onto another unit, and causes their HP, fuel, and ammo to be combined, but this may not exceed the maximum values for each; excess HP is converted into funds. The units involved must not be carrying another unit.
Loading occurs when a unit is moved onto the same space as a transport unit. The unit is loaded into the transport, and moves around with it. While loaded units cannot be damaged in any way (including CO Powers), but they are destroyed if the transport is destroyed. Units can then be dropped onto an empty square next to a transport, but they automatically end their turn and cannot move until the next day.