As the Allied air campaign against German interests during World War 2 increased in both its intensity and results, it fell to the German Army to develop mobile-minded air defense platforms. The earlier "Mobelwagen" was born from the hull of the Panzer IV medium tank and fitted with a single 37mm FlaK 43 L/89 autocannon affixed to an boxy armored superstructure. The vehicle weighed some 24,000 kilograms, featured a crew of six and managed an ammunition load of 416 x 37mm projectiles. For all intents and purposes, the Mobelwagen became an interim design until better air defense vehicles could be found.
Thus came about the "Wirbelwind" ("Whirlwind"/ "Flakpanzer IV") which was also built atop the hull of the Panzer IV line. Instead of a single gun, a crew of six and a boxy superstructure, the Wirbelwind utilized a quad-gun arrangement (4 x 2cm Flakvierling 38 L/112.5) with a crew of five and an all-new, open-air, nine-sided turret "tub". The Panzer IV tank origins were clearly visible with the eight road wheel arrangement, forward-mounted drive sprocket and rear-mounted track idler. The crew consisted of a driver, commander (doubling as the primary gunner), radioman and two ammunition handlers. Total ammunition stocks were 3,200 x 20mm projectiles for the four cannon and 1,350 x 7.92mm ammunition for a single, defensive-minded, MG34 machine gun. The vehicle retained the Panzer IV's leaf spring suspension and could make headway at 25 miles per hour on ideal surfaces and reach out to a range of 124 miles. Power was through a Maybach HL 120 TRM 12-cylinder gasoline-fueled engine held at the rear. Armor protection ranged from 10mm to 80mm across the various facings.
Only when pressed with the need for protection against Allied attack aircraft did the German Army invest in air defense vehicles and then began a race to find appropriate solutions. Design and development of the Wirbelwind began in 1944 when a German officer - Karl Krause - brought his Panzer IV-based idea to authorities to which the design was ultimately approved by Hitler himself. Work then began on existing stocks of Panzer IV vehicles for the conversion process ahead. In many ways, the Wirbelwind offered a logistically-friendly solution, able to retain and reuse many of the automotive components already in circulation for the Panzer IV tank and the new faceted turret was simple enough to mass-produce. Additionally, the 20mm guns were available in number. Manufacture of Wirbelwinds was charged to Ostbauwerke of Sagan, Silesia.
In early-action use, the Wirbelwind proved valuable against low-flying aircraft through its four-gun, repeat-fire arrangement. Its self-propelled capabilities allowed it to relocate with some ease and keep up with German convoys when required. However, Allied air power and related tactics against ground fire continued to evolve which, in turn, began limiting the effectiveness of the Wirbelwind system. The 20mm shell-of-choice also showcased its limitations which furthered other air defense solutions - one coming in the form of the "Ostwind", another Panzer IV-based vehicle reverting back to the more potent 3.7cm FlaK 43 gun within a new, open-air, six-sided turret design. Despite its now-limited air defense capabilities, Wirbelwinds continued in support of German Army actions as its 20mm quad-guns could be brought to bear against enemy light-armored ground targets and troop concentrations with rather disastrous results.
Around 100 or so Wirbelwind vehicles were ultimately completed, though precise numbers are not recognized in any one source.
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