During WW2 the Germans fielded many rocket systems and among them were portable Nebelwerfers that displayed awesome firepower. So it was only a matter of time until someone decided to mount a launcher on a vehicle for better mobility and fire support. Opel took the job of converting 3 ton LKWs into semi-tracked 7 ton armored Maultiers (Mules) which mounted a single 7.92mm MG-34 or 42 and 6x 150mm rockets (-12/+80o depression/elevation). Around 600+ were produced from April 1943-May 1944, half as munitions carriers and half as rocket launchers. Their firepower was devastating, but b/c of the smoke trails they had to move frequently. Some mounted tank smoke dischargers as a barrier when Allied aircraft came around hunting. This was AFAIK the first real attempt at a MLRS, not just mounting inclined rockets on ramps from trucks or rocket racks on tanks as the Soviets, British, and US used. This was a dedicated system and built as such. Waffen SS versions carried 24x 80mm rockets on twin rails while the 150mm Heer rockets were in launch tubes.