Up to five air factors may base at a city, or at an airbase counter (each major power has three of these, one of which may be placed each turn - once placed it can only be moved by SR or relocated to the country's capital if out of supply). Initially Germany has 6 air units and Italy 2 (i.e. 40 factors), against three British and two French (i.e. 25 factors). By the end of the war 5 German air units (i.e. 25 air factors, assuming some have been transferred to fight Allied bombers) might be facing 5 US, 4 British and 3 Soviet (i.e. 60 air factors). Air units may be voluntarily split up, and single factors may be rebuilt provided they are combined by SR to form a complete air unit.