The Flakpanzer IV Kugelblitz ("ball lightning") was a German self-propelled anti-aircraft gun developed during World War II. By the end of the war, only a pilot production of five units had been completed. Unlike earlier self-propelled anti-aircraft guns, it had a fully enclosed, rotating turret. The need for a specialised self-propelled anti-aircraft gun, capable of keeping up with the armoured divisions, had become increasingly urgent for the German Armed Forces, as from 1943 on the German Air Force was less and less able to protect against enemy fighter bombers. Therefore a multitude of improvised and specially designed self-propelled anti-aircraft guns were built, many on the Panzer IV chassis, starting with the Flakpanzer IV Möbelwagen and progressing through the Wirbelwind and Ostwind models. The Kugelblitz was the final development of the Flakpanzer IV. The first proposal for the Kugelblitz envisioned mounting a modified anti-aircraft turret developed for U-boats on the Panzer IV chassis, which was armed with dual 30 mm MK 103 Brunn guns (a configuration known as Doppelflak, "dual flak"). This was however abandoned as impractical, as development of this gun had not yet been completed, and in any case the entire production run of this gun turret was reserved for the German Navy. Instead, the 30 mm Zwillingsflak ("twin flak") 103/38 twin gun, a twinned-mount version of the MK 103 cannon, was used, which had also been fitted to such planes as the Henschel Hs 129 and Dornier Do 335. The rate of fire of the twin 30 mm guns was 450 rounds a minute per gun. The Kugelblitz had the chassis and basic superstructure of the Panzer IV tank, on which a newly designed turret was mounted. This turret was fully enclosed, with overhead protection and 360° traverse. As production of the Panzer IV was about to be terminated further work was under way to change to the Jagdpanzer 38(t) chassis which was in turn based on the Panzer 38(t). No prototypes based on Hetzer hulls were completed.