During the Belgian Campaign of 1940, it initially held defences at Liège but was forced to retreat by the German XVI Panzer Corps. The Battle of Fort Eben-Emael occurred along the Corps' defensive line. German planners had recognised the need to eliminate Fort Eben-Emael if their army was to break into the interior of Belgium. It decided to deploy airborne forces ("Fallschirmjäger") to land inside the fortress perimeter using gliders. Using special explosives and flamethrowers to disable the defences, the "Fallschirmjäger" then entered the fortress. In the course of the battle, German infantry overcame the defenders of the I Belgian Corps' 7th Infantry Division in 24 hours.