Raupenschlepper Ost, literally "Caterpillar Tractor East", is more commonly abbreviated to RSO. This fully tracked, lightweight vehicle was conceived in response to the poor performance of wheeled and half-tracked vehicles in the mud and snow during the Wehrmacht's first winter on the Soviet Front. The RSO may have been inspired by very similar full-tracked small tractors in use in other armies (such as the Soviet STZ-5 "Stalingradec", and the U.S. Army's own M4 Tractor), mostly originated from the pre-war light to medium series of Vickers artillery tractors.