The Flakpanzer IV "Wirbelwind" (Whirlwind in German) was a self-propelled anti-aircraft gun based on the Panzer IV tank. It was developed in 1944 as a successor to the earlier self-propelled anti-aircraft gun Mobelwagen. It is estimated that less than 100 of these were produced during WWII. [YOUTUBE]cxrSFKL3fkA[/YOUTUBE]