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 "Stalingradets", 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.
Cargo carrier variant: RSO
History
After the Wehrmacht's first fall and winter (1941–1942) on the Eastern Front, they found that the extremely primitive roadways in the USSR and seasonal mud required a fully tracked supply vehicle to maintain mobility. Steyr responded by proposing a small, fully tracked vehicle based upon its truck, the Steyr 1500A light truck, already in use in the army. The vehicle was introduced in 1942 as the Raupenschlepper Ost (RSO).
Initially designed as a prime mover and artillery supply vehicle, it eventually served in a wide variety of roles. Immediately after the vehicle reached the Eastern front, the combat units started using it for general transport duties. It gave outstanding service due to its reliability, its ease of maintenance, and its capability to take over a variety of roles - in every kind of terrain - that other vehicles lacked. The four road wheels per side, all in a single line as part of a "slack-track" system with no return rollers, comprised a much simpler suspension system, much more able to handle the rasputitsa mud season and Russian winter conditions, without mud or snow freezing between the wheels of the complex overlapping/interleaved Schachtellaufwerk suspension systems that German half-track vehicles like the Sd.Kfz. 7 possessed. Soon the orders for the RSO surpassed Steyr's production ability, and more manufacturers joined the vehicle's production in order to meet the ever increased demands.
Description
The original version had a pressed-steel cab with a truck-like configuration similar to the wheeled trucks. The next two versions – RSO/02 and 03 – had a simpler, soft-top, slab-sided metal cab. All models had wooden, drop-side cargo beds typical of light trucks of the era. It had a ground clearance of and was originally powered by a Steyr V8 petrol engine of 3.5 L giving , which in the RSO/03 Magirus-produced vehicles was replaced by a Deutz air-cooled diesel engine.
The later model used a Cletrac-type final drive (instead of the automotive-type differential unit used previously) along with many other improvements. The engine was mounted on the floor of the driving cab with the drive taken through a single plate clutch to the transmission. The transmission had four forward gears and one reverse. The suspension consisted of four large pressed-steel disk wheels on each side, mounted in pairs with elliptic springs. Steering involved upright steering levers to four hydraulic brakes on the sprockets and idlers. A spring-loaded pintle was fitted at the rear, and towing hooks were fitted in the front. It had a speed of about .
The Kingdom of Romania purchased 100 RSO/01 tractors in 1943. These were used for towing anti-tank guns.
Anti-tank variant: RSO/PaK 40
By 1943 infantry anti-tank units at the front complained strongly that it was almost impossible to move their guns using trucks at daylight under enemy fire, leading to enormous losses of equipment during "emergency relocations" (at the time a euphemism for withdrawal), and their opinions reached the top ranks. OKW explored a previously considered proposal to fit the 7.5 cm PaK 40/1 anti-tank gun – by then the standard PaK used by the Wehrmacht - on top of an RSO chassis. After seeing the blueprints, Hitler ordered a limited production run for combat testing, before the prototypes were completed.
The project was carried out by Steyr. The suspension of the RSO remained unchanged, but the front driver's compartment was replaced with a low, lightly armoured superstructure. The result was a lightweight, cheap to produce, and highly mobile infantry anti-tank weapon. It was more exposed compared to the conventional, open-topped Panzerjäger style of tank destroyer, which had a construction cost many times that of a RSO/PaK 40.