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.
The Flakpanzer is a vehicle featured in Battlefield 1942: Secret Weapons of WWII, issued to the Waffen SS. The Flakpanzer is essentially a flak gun placed on top of a tank. The person in the tank's first position has a machine gun to use and drives the vehicle -- although the machine gun is mounted co-axially and can only fire in a narrow arc facing the front of the vehicle -- and the person in the second position controls the flak gun. The flak gun has a full range of motion, like a normal flak gun. The flak gun on this tank fires a bit faster than that of a normal flak gun, but it can overheat.