The appearance of the T-34 in 1941 caused a crisis for German antitank forces. Existing antitank guns were nearly impotent against the new Russian tank, while antiaircraft and artillery pieces, though successful when pressed into action, were insufficiently mobile to accompany mechanized forces. The German Army Ordnance Office, the Heereswaffenamt, was responsible for development of new weapons and would be responsible for countering the threat of Russian armor. The Heereswaffenamt would need to not only counter the T-34, but also do so in an environment of shifting political relationships and with an increasingly stressed industrial system. Utilizing lessons from the bitterly contested battlefields of western Russia, the Heereswaffenamt developed a tankdestroyer, the Jagdpazer IV, using the existing chassis of the Panzer IV tank, and the guns of both the Panzer IV and Panther tanks. The Jagdpanzer IV, known by its crews as GuderianŸs Duck, proved to be a capable tank killer against both the T-34 threat of 1941 and 1942, as well as the improved versions of 1943 and 1944.