The Panzer IV's invincibility had been disproven by the Red Army, by its desperate but effective resistance against the German Army during the latter's Operation Barbarossa, or the invasion of the Soviet Union. The Panther appeared in November 1942. It had a 75mm gun, which could penetrate the armor of almost all Soviet tanks. Other design features included sloped armor, torsion-bar suspension, and interleaved wheels. The armor was 80mm thick, with a 650 horsepower engine capable of speeds of up to 28 MPH. Between 1942 and 1945, when World War II ended, Germany produced over 4,800 Panther tanks.