 Complete the following phrase:  Prior to World War I, the German military was especially interested in the development of superweapons due to the need for the Schlieffen plan to march past a line of Belgian fortifications constructed specifically to stop such an invasion route. During the opening phases of the war, the Germans employed a 420 mm Krupp howitzer the Big Bertha and two 305 mm Skoda Mörser M. 11 mortars to reduce the famous fortresses of 