Panzerkampfwagen IV "Wirbelwind" (Whirlwind) armed with four 20mm (.78 caliber) automatic cannon. The Wirbelwind was built on war-weary repaired Panzer IV chassis. Sources differe on the total number built, but it was between 87 and 105. The 20mm cannon were found to be not as effective as a 37mm (1.46 inch) round, so the Wirbelwind was planned to be replaced with the "Ostwind" (East Wind) which mounted a single 37mm cannon. Either version could be used against infantry with devastating results. The Wirbelwind concept was developed by Karl Wilhelm Krause, an officer with the 12 SS Division "Hitlerjugend." Both the Wirbelwind and the Ostwind were very effective against low flying aircraft, but were not built in sufficient numbers to suppress Allied aircraft. The mobility the platform afforded to panzer units was highly desired. Several Wirbelwind accompanied Kampfgruppe Peiper during the Ardennes Offensive; they were all destroyed or abandoned during the operation.