The Colossus The Großkampfwagen or "K-Wagen" (short for G.K.-Wagen) was a German super-heavy tank, two prototypes of which were almost completed by the end of World War I. In June 1917, before the first A7V tanks had been completed, the German War Ministry ordered the development of a new superheavy tank intended to be used in break-through situations. Design work was carried out by Joseph Vollmer, a Reserve Captain and engineer working for the Verkehrstechnische Prüfungskommission ("Transport