Hauptmann Koch divided his force into four assault groups. Group Granite, under Oberleutnant Rudolf Witzig, composed of eighty-five men in eleven gliders whose task would be to assault and capture Fort Eben Emael; Group Steel, commanded by Oberleutnant Gustav Altmann, and formed of ninety-two men and nine gliders, would capture the Veldwezelt bridge; Group Concrete, commanded by Leutnant Gerhard Schacht and composed of ninety-six men in eleven gliders, would capture the Vroenhoven bridge; and Group Iron, under Leutnant Martin Schächter, composed of ninety men in ten gliders, who would capture the Kanne bridge. The crucial element for the assault force, particularly Group Granite, was time. It was believed that the combination of a noiseless approach by the gliders used by the assault force, and the lack of a declaration of war by the German government, would give the attackers the element of surprise. However, German estimates were that this would last, at the most, for sixty minutes, after which the superior numbers of the Belgian forces defending the fort and the bridges, as well as any reinforcements sent to the area, would come to bear against the relatively small number of lightly armed airborne troops. The German plan, therefore, was to eliminate within those sixty minutes as many anti-aircraft positions and individual cupolas and casemates as was possible, and at all costs to put out of action the long-range artillery pieces which covered the three bridges. The destruction of these guns was expected to be completed within ten minutes; within this time the airborne troops would have to break out of their gliders, cover the distance to the guns, fix the explosive charges to the barrels of the guns and detonate them, all while under enemy fire.
