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 Mobelwagon. It is believed that either 87 or 105 Wirbelwinds were produced during the war, but due to discrepancies between the recorded production numbers at Ostbau Werke and Wehrmacht service records, the exact number will probably never be known.