Raupenschlepper Ost (RSO)

Raupenschlepper Ost (German: "Caterpillar Tractor East", more commonly abbreviated to RSO) was a fully tracked, lightweight vehicle used by the Wehrmacht in World War II. It was conceived in response to the poor performance of wheeled and half-tracked vehicles in the mud and snow during the Wehrmacht's first autumn and winter on the Soviet Front.

The RSO was a contemporary with somewhat similar Allied full-tracked small artillery tractors in use in other armies (such as the Soviet STZ-5 "Stalingradec", and the U.S. Army's M4 Tractor), mostly originated from the pre-war light to medium series of Vickers artillery tractors.

Two variants of this vehicle were built: the basic cargo carrier, and a self-propelled antitank vehicle armed with a PaK 40 gun. Both shared the same chassis.

https://en.wikipedia.org/wiki/Raupenschlepper_Ost