After development at Erhard & Söhne, the mechanical engineering company Boehringer in Göppingen took over production. The construction of the last two prototypes, the U5 and U6, also began in Schwäbisch Gmünd but they were completed in Göppingen. The prototype vehicles were fitted with the Mercedes-Benz M 136 petrol engine from the Mercedes-Benz 170 V (W 136) passenger car.
For series production, however, the brand with the star supplied the new, high-speed OM 636 diesel engine (28 kW/38 PS) as the power unit. In the interests of long-term durability, especially in the harshest conditions, the output was limited to 18 kW (25 PS) and a maximum engine speed of 2500 rpm for use in the Unimog.