Despite the views of Estienne and later Charles de Gaulle, the French general staff failed in defining an effective military doctrine regarding their use, due to the division of labour between infantry and cavalry tanks. In the Battle of France, despite an advantage in number and armour against the Germans, the French tanks were not used to good enough effect. The infantry tanks were only effective in executing the breakthrough phase of a battle; and thus useless as a mobile reserve. Ironically, cooperation with the infantry was poor. The Cavalry units alone were too few in number.