The 8.8 cm Flak 18/36/37/41 is a German 88 mm anti-aircraft and anti-tank artillery gun from World War II. It was widely used by Germany throughout the war, and was one of the most recognized German weapons of that conflict. Development of the original model led to a wide variety of guns. The name applies to a series of related guns, the first one officially called the 8.8 cm Flak 18, the improved 8.8 cm Flak 36, and later the 8.8 cm Flak 37. Flak is a contraction of German Flugzeugabwehrkanone meaning "aircraft-defense cannon", the original purpose of the weapon. In English, "flak" became a generic term for ground anti-aircraft fire. In informal use, the guns were universally known as the Acht-acht ("eight-eight") by Germans and the "eighty-eight" by the Allies. The versatile carriage allowed the 8.8 cm FlaK to be fired in a limited anti-tank mode when still on its wheels; it could be completely emplaced in only two and a half minutes. Its successful use as an improvised anti-tank gun led to the development of a tank gun based upon it: the 8.8 cm KwK 36, with the "KwK" abbreviation standing for Kampfwagen-Kanone (literally "battle vehicle cannon", or "fighting vehicle cannon"), meant to be placed in a gun turret as the tank's primary armament. This gun served as the main armament of the Tiger I heavy tank.