Hitler ordered in may 1942 a new simple 5 ton low-speed tractor wich can be use as an load carrying halft-track for use on the Eastern Front and should replace the Sd.Kfz 6 and Sd.Kfz 11 as well as the various lesser-known vehicles of the same class. The task was giving to Büssing-NAG. After series of testing, the design was adopted in production as the Schwerer Wehrmachtschlepper or sWS, wich means Heavy Military Tractor in German, in december 1943. Early models used a unarmored truck cabin similar to the earlier Sd.Kfz. half-tracks it replaced, while later examples featured an armored cabin and engine compartment that looked similar to the famous Sd.Kfz. 251 APC's. Meanwhile Tatra will also produce the sWS, but both factory's will only produce around 825 vehicles. Same like many other halftracks, like the Sd.Kfz 7 (Sd.Kfz. 7/1) and the Sd.Kfz. 10 (Sd.Kfz. 10/4 and Sd.Kfz. 10/5), the sWS will also be used as carriage for anti-air guns but also for rocket launchers. On an armored cabine version, with behind an armored casemat, an 10 barreled 15 cm Nebelwerfer 41 "Screaming Mimi", or "Moaning Minnie", rocket launcher will be built on the casemat. Wich become the 15 cm Panzerwerfer 42 auf Schwerer Wehrmachtsschlepper or Panzerwerfer auf SWS. The 15 cm Nebelwerfer 41 use the 15cm Wurfgranate Spr. High-Explosive missiles. Each missile weights 31.8 kg included 2.5 kg TNT and can reach a range off 6,900 metres. The vehicles should can fire 10 rpm. Another version of the Panzerwerfer 42 was the 15 cm Panzerwerfer 42 auf Selbstfahrlafette Sd.Kfz.4/1, based on the Opel Maultier Half-Track.