French units may not stack with British units - they may commit Ground Support to each other's attacks, as this flies over the German defenders, but not Defensive Air Support - nor may British units enter Paris nor the Maginot Line, but they may conduct joint attacks. France is controlled by the Soviet player if there is no separate French player. Soviet units may not stack or combine with Western Allied units for combat, although the Allies may send a small expeditionary force (of no more than ten factors, i.e. about three corps) to fight in the USSR - this facility was removed from later versions of the game system. Britain and the USA share victory conditions, and their units may always stack and fight together.