Raupenschlepper , Ost 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 . Ost . After the Wehrmacht ' s first fall and winter ( 1941 – 1942 ) on the Russian front , they found that the extremely primitive roadways in Russia and seasonal mud required a fully tracked supply vehicle to maintain mobility . Steyr responded by proposing a small , fully tracked vehicle based upon its 1 . 5 - tonne truck ( 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 SdKfz 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 . 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 truck s of the era . It had an impressive ground clearance for its size of 55 cm and was originally powered by a gasoline Steyr V8 cylinder engine of 3 . 5 l giving 85 hp , which in the RSO / 03 Magirus - produced vehicles was replaced by a superb ( although of lower power - 66 hp - ) Deutz diesel air - cooled 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 30 km / h . 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 - on top of an RSO chassis . After seeing the blueprints , Hitler ordered a limited production run for combat testing before the test vehicles 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 " panzerjager s " of which construction cost many times an RSO / PaK 40 . Although the vehicle was intended for use by the infantry anti - tank units , all pre - production vehicles were issued to armoured units ( Panzer Jager " Abteilungen " 743 and 744 , and 18th " Panzergrenadier " Division ) , due to the urgent need for replacements . Their low speed and light armour inevitably resulted in problems for these units trying to cooperate with those in other fighting vehicles . The German Army Group South , where the units issued for combat testing , declared the vehicle useful , and large - scale production was quickly authorised . Despite the decision to have Steyr shift its entire production line into RSO / Pak 40 , no specific order reached industry , and only the approximately 60 pre - production vehicles were ever manufactured . While the first vehicles were rolled out from the production line , Steyr started testing an improved version that incorporated a wider chassis and tracks ; these changes improved cross - country performance and lowered the center of gravity , an issue in a vehicle of such a high ground clearance . None of the improved version ever reached the front . In October 1943 , Steyr was ordered by the Ministry of Munitions to cease production of any type of tracked vehicles . By then a new up - gunned version of the widened chassis had been designed and was planned to enter production in 1944 ; it had a more powerful and less noisy V8 petrol engine to carry the 88mm Pak 43 L70 gun , by far the most powerful anti - tank weapon of its era designated PzJag K43 . It is doubtful if any had been constructed by the end of the war . Approximately 23 , 000 RSO of all versions were produced by Steyr ( 2 , 600 pcs ) , Klockner - Deutz - Magirus ( 12 , 500 pcs ) , Wanderer - Auto - Union ( 5 , 600 pcs ) and Graf & Stift ( 4 , 500 pcs ) .