The Flakpanzer IV 'Wirbelwind' ('Whirlwind') was a self-propelled anti-aircraft gun based on the Panzer IV. It was developed in 1944 as a successor to the earlier self-propelled anti-aircraft gun named the 'Mobelwagen'. or 'Furniture Van'. The Panzer IV's turret was removed and replaced with an open-top, nine-sided turret which housed a quadruple 2 cm Flakvierling 38 L/112.5. The combination of armour and rapid fire from the four guns of the Wirbelwind also made it effective against ground targets.