The development of the heavy German army tractor (s.W.S.) began in 1942 as a replacement for the 5 tonne half-track truck (Sd. Kfz. 6). The approx. 1000 vehicles built were mainly used with a platform superstructure as a supply vehicle for the troops. By the end of World War II dozens of vehicles were also equipped as a self-propelled mount for the 3.7 cm Flak 43 gun. In addition to the additional protective armour for the engine and driver's cab, these vehicles had a reinforced chassis to bear the weight of the anti-aircraft gun and the munitions. The further improved 3.7 cm Flak 43 gun delivered from 1944 onwards weighed only 1,392 kg and the practical firing speed was increased to 150 rounds per minute.