The plan, "Fall Festung", had been developed by Hitler. If the first attack did not succeed, the bridges at Rotterdam, Dordrecht and Moerdijk would be captured to allow a mechanised force to move in. This force was to be the German 9th Panzer Division. They were the only German armoured division having just two tank battalions. the total number of tanks in the group was 141. The plan was for them to go through a gap in the Dutch lines created by the 254th and 256th Infantry Divisions. Then they would join up with them, forming the "XXVI. Armeekorps". At the same time, an attack would be made against the Grebbe Line in the east by the 207th and 227th Infantry Divisions, united to form "X. Armeekorps", to fight the Dutch Army. The plan was to force the Dutch back to the east front of the Fortress Holland or beyond. If the Dutch did not surrender on the first day, the Eighteenth Army would attack Fortress Holland on the third day from the south.