During WWII, the Flakvierling 38 was used as an antiaircraft gun against low altitude fighter-bomber aircraft. The original single-gun Flak 38 was improved upon with the 4x20mm Flakvierling 38 coming about. The weapon could fire at a maximum rate of 1,800 rounds per minute and even the regular rate of 800 rounds per minute was a force to be reckoned with. It was feared by allied fighter pilots who called it "the Four-Barreled Demon". It was a compact gun that could be quickly set up anywhere thanks to its trailer, and was widely used to defend airfields. In addition, they were also mounted on various vehicle platforms serving as mobile antiaircraft guns defending German airspace.