Weapon Carrier or SPG?
The German’s experimented with transporting and mounting a number of different guns on the back of the Raupenschlepper Ost light ‘prime mover’ tracked vehicle. The name Raupenschlepper Ost is translated to “Caterpillar Tractor East”. It is commonly abbreviated to just RSO.
The prototypes were shown to the army. The Raupenschlepper Ost 7.5 cm Pak 40 tank destroyer self-propelled gun went into production. Between 80 and 90 were produced. Most saw action on the Eastern Front. A version of the RSO that carried a 2cm Flak38 anti-aircraft gun mounted to the floor of the rear wooden cargo bay also saw service.
At present no documentation has been found relating to the mounting and carrying of artillery guns on the back of the Raupenschlepper Ost even though there are surviving photographs of four different prototypes: the 7.5 cm GebH 36 auf RSO/3; 7.5 cm Gebh 34 auf RSG; 10.5 cm GebH 40 auf RSO/1 and 15 cm sIG 33 auf RSO/3.
It is not clear if these prototypes were going to be used as a Waffenträger weapon carrier or as a Selbstfahrlafette Geschuetzwagen, a self-propelled artillery gun.
This is why a weapons carrier was a good idea. Towed guns could become waterlogged and covered in mud.
If they were used as a Waffenträger then how was the gun dismounted? There is photographic evidence that the guns were loaded on the vehicle by a winch attached to a freestanding metal frame on a hard surface. Another photograph shows a Raupenschlepper Ost reversed back towards an earthen ramp so the gun could be pushed onto the back of the vehicle.
On a battlefield, it would be difficult to build a ramp quickly or make sure there was a hard surface for a winch and frame to be constructed on to enable the guns to be unloaded. The guns were heavy and if the load bearing frame was put together on soft earth its legs would sink into the ground under the weight.
If these prototype vehicles were intended to be used as a Selbstfahrlafette Geschuetzwagen, or self-propelled artillery guns, the problem the engineers would have to overcome was the recoil.
With the artillery gun mounted in the back of the vehicle, they were very top heavy and had a high center of gravity. There was a danger that the RSO would topple over.
It can be theorized that two of the prototypes were intended to be used as artillery SPGs but tests showed the RSO chassis was not strong enough to take the gun recoil so they were never put into production. This is supported by the fact that on the photographs of the 7.5 cm GebG 36 auf RSO/03 the side panels are down and it can be seen that the gun wheels had been clamped to the deck of the vehicle and the gun ‘tails’ had been shortened. The 7.5 cm Gebirgshaubitze 34 auf Gebirgsraupenschlepper (RSG) also carried a similar sized howitzer.
7.5 cm GebG 36 auf RSO/3
The other two prototypes seen in photographs are carrying much bigger 10.5cm and 15cm howitzers. There is no evidence that these guns were bolted to the wooden cargo bay of the RSO tracked vehicle so that it could be fired. The gun’s split trail legs had not been modified to fit the length of the vehicle. They protrude out the back and the rear ‘spades’ are carried in the back of the vehicle for use when the gun is set up on land again. The RSO tracked vehicle is being used as a Waffenträger weapon carrier in these examples.
The Raupenschlepper Ost RSO tracked vehicle
The RSO light ‘prime mover’ tracked vehicle had a very basic suspension design with all steel wheels and just four small leaf springs. This made it cheap and easy to produce. It had high ground clearance and excellent performance in poor terrain. It was a tracked version of the Steyr 1½-tonne truck. It could carry a 1,500 kg (3,307 lb) load in its cargo bay.
The Steyr-Daimler-Puch manufacturing company designed the Raupenschlepper Ost (RSO) to be used to tow field guns and transport supplies over rough ground in muddy waterlogged and snowy conditions. They were in production between October 1943 and May 1944: Steyr-Daimler-Puch produced 2,600 vehicles; Klockner-Deutz-Magirus (KHD) manufactured 12,500; Auto-Union made a further 5,600 and Graf & Stift constructed 4,500 RSOs. They were used extensively on the Eastern Front.
There were four main variants. The RSO/01, RSO/02 and RSO/PaK40 were powered by a 3.5L Steyr V8 gasoline/petrol 70hp engine. The RSO/03 had a better performing Deutz F4L514 5.3L 4-cylinder air-cooled diesel engine although produced lower horsepower at 66hp.
RSO/01 towing a field gun
The RSO/1 had a fully enclosed pressed steel rounded cab with a wooden rear cargo bay. The RSO/2 had a flat sided metal cab. The RSO/3 was manufactured by KHD at their Magirus Factory and had a simplified slab-sided metal cab. The RSO/PaK40 had a lightly armored low profile steel cab to enable the 7.5cm PaK40 anti-tank gun mounted on the rear flat rear bed wooden cargo bay to fire forward.
RSO/3 fully tracked artillery prime mover
7.5 cm Gebirgshaubitze 36 auf Raupenschlepper Ost (RSO/3)
To mount the 7.5cm Gebirgsgeschütz 36 (7.5 cm GebG 36) light mountain howitzer on the back of the Raupenschlepper Ost tracked vehicle cargo bay the spades at the end of the split trail legs were removed. The legs were also cut down in length to allow the back tail gate to be raised. The wheels were bolted to the wooden floor in a special semi-circular frame. This gun was meant to be fired from the back of the RSO. It could no longer be dismounted and fired from the ground without having new split trail legs fitted. It could not function as a Waffenträger weapon carrier. It was a Selbstfahrlafette Geschuetzwagen, a self-propelled artillery gun prototype.
7.5cm Gebirgsgeschütz 36 (7.5 cm GebG 36) light mountain howitzer mounted on the rear of an RSO/3
The gun was built by Rheinmetall to replace the World War One mountain divisions (Gebirgs Divisionen) guns. Between 1938 and 1945, records show 1,193 were built. It was a standard German horizontal sliding breech block gun with a muzzle brake. It used a variable recoil system that shortened the recoil as the elevation increased to stop the gun breach hitting the ground. Rear trunnions were added to lengthen the distance between the breech and the ground. The recoil mechanism was hydropneumatic, with both buffer and recuperator positioned below the barrel.
To keep the weight down the gun was fitted with light-alloy disc wheels with rubber rims. No protective gun shield was fitted to save weight. It weighed 750 kg (1,650 lb) so it was within the cargo weight limit of the RSO.
When used on the ground, the 7.5 cm GebG 36 would jump when fired at low angles, because of its lightness. The strength of the recoil would force the gun’s trail spades to act as a fulcrum and lever the wheels upwards. The shell canister bag charge 5, the largest propellant increment, was forbidden to be used at near horizontal angles under 15° because the gun would jump excessively. When the gun was fired at higher angles it performed better as the ground absorbed any residual recoil forces not absorbed by the recoil system. On the back of the RSO the vehicles suspension, tracks and the ground had to absorb the force of the recoil from the gun.
The 7.5cm Gebirgsgeschütz 36 mountain howitzer used two-part ammunition, with four bag charges of propellant that were added together depending on the range of the target. A larger 5th charge bag was used on its own when the target was at the limit of the howitzers maximum range. It fired a high explosive HE 5.83 kilograms (12.9 lb) shell that had a maximum range of 9.25 km (10,120 yards). It could also fire smoke shells and in an emergency a hollow charge armor piercing AP rounds at short range. A good gun crew was able to produce a rate of fire of six to eight rounds per minute.
This mountain gun could be broken down into six separate parts, each having a maximum weight of 300 pounds. This ability enabled the weapon to be easily transported by pack animals or in an airplane.
The gun’s 56-inch barrel was of a monobloc construction. To enable larger more powerful charges to be used and to increase the range of the gun without damaging the gun barrel, it was fitted with a perforated, six-baffled muzzle brake.
7.5 cm GebH 36 auf Gebirgsraupenschlepper (RSG)
Gebirgsraupenschlepper (RSG) with a 7.5 cm Gebirgshaubitze 34 mountain howitzer mounted on its rear cargo bay next to a RSO/3 tracked vehicle.
This photograph shows the smaller Steyr made Gebirgsraupenschlepper (RSG) mountain troop tracked vehicle next to the larger Raupenschlepper Ost (RSO/3) vehicle. There is a 7.5 cm Gebirgshaubitze (GebH) mountain howitzer mounted on the back of the RSG. Only one photograph has been found so far of this prototype artillery self-propelled gun. The photograph below has been enlarged and edited.
The problem is that the caption that went along with this photo identified the gun on the back as a captured Belgium army Swedish built Bofors 75 mm Model 1934 mountain gun (Canon de 75 mle 1934). It was recorded as a 7.5 cm Gebirgshaubitze 34 auf RSG, but this gun was not fitted with a circular perforated muzzle brake.
It can be theorized that the howitzer on the back is the same gun used on the 7.5 cm Gebirgshaubitze 36 auf Raupenschlepper Ost which does have a circular perforated muzzle brake. Just like on the other vehicle, it would have had its split tail legs cut to fit the length of the wooden cargo bay and the wheels clamped to the floor so that the gun could be fired from the back of the vehicle.
7.5 cm Gebirgshaubitze 34 auf Gebirgsraupenschlepper (RSG)
RSG – Gebirgsraupenschlepper – Caterpillar Tractor for Mountain Troops – Vienna Military Museum
Illustration of the sIG33 auf Raupenschlepper Ost conversion by David Bocquelet
10.5 cm Gebirgshaubitze 40 mountain howitzer on the back of a Raupenschlepper Ost (RSO/1)
7.5 cm Gebirgsgeschütz 36 German mountain howitzer
10.5 cm GebH 40 howitzer – Photo – Yuri Pasholok
The 15 cm sIG 33 (schweres Infanterie Geschütz 33) was the standard German heavy infantry gun used in the Second World War – unknown modeler
10.5 cm Gebirgshaubitze 40 auf Raupenschlepper Ost (RSO/1)
There is a poor quality photograph showing a 10.5 cm Gebirgshaubitze 40 (10.5 cm GebH 40) mountain howitzer on the back of a Raupenschlepper Ost (RSO/1).
In the picture, it looks like the vehicle has been backed up to ramp of earth. There appear to be wooden planks spanning the gap between the top of the earth mound and the back of the RSO/1. Its tail gate is hinged down and so are the wooden side panels. These wooden planks would have been used to enable the gun to be pushed onto the back of the vehicle.
10.5 cm GebH 40 auf RSO
Unlike on the photographs of the 7.5 cm Gebirgshaubitze 36 auf Raupenschlepper Ost (RSO/3), there is no visible evidence that the larger 10.5cm GebH 40 gun had been fixed to the wooden floor of the cargo bay. The split trail legs had not been cut and shortened. They projected over the rear of the vehicle.
There was no special semi-circular locking wheel frame in use. The spades that were normally fitted to the end of the split trail legs had not been attached. Their triangular shape can be seen at the back of the gun.
Was this photograph taken of an early live firing trial to see if the RSO/1 could take the gun recoil or just to see if it could take the weight of the gun? It is not known, as no documents have been found so far.
In the other surviving photographs the gun is seen on the back of the RSO/1 with the wooden side panels in the up position, the split trail legs sticking out the back and the tail spades loaded on the rear with the tail gate panel in the down position.
10.5 cm GebH 40 mountain howitzer on the back of a Raupenschlepper Ost (RSO/1)
The RSO/1 tracked vehicle has the manufacturing company’s name and logo on the side. This is a factory vehicle, not one that has been sold to the army. It is safe to assume that it is the company, Steyr-Daimler-Puch, who was experimenting with showing that the 10.5cm GebH 40 mountain howitzer can be transported on the back of their vehicle.
10.5 cm Gebirgshaubitze 40 (10.5 cm GebH 40) carried on the rear of an RSO/03.
In these three, better quality photographs it looks like a frame and winch had been used to lift the gun onto the back of the RSO/1. These photographs would suggest that this vehicle was being used as a Waffenträger weapon carrier. At present, there is no evidence to suggest the vehicle was used as a Selbstfahrlafette Geschuetzwagen, a self-propelled artillery gun, and fired from the back of the cargo bay, as there are no visible mountings or fixings to secure the gun to the vehicle.
10.5cm Gebirgshaubitze 40 mountain howitzer being loaded on the back of an RSO/1 by winch and frame
There only appears to be photographs of a 10.5 cm Gebirgshaubitze 40 mountain howitzer on the back of one RSO tracked vehicle. It is highly unlikely that the experiment was a success as the weight of the gun exceeded the designed load weight of the vehicle. The gun weighed 1,660 kg (3,660 lb) and the RSO’s load weight limit was 1.500 kg (3,307 lb). The RSO’s center of gravity would have been significantly raised. Both these things would have made the vehicle tricky to drive.
15 cm sIG 33 auf Raupenschlepper Ost (RSO/3)
15 cm sIG 33 auf Raupenschlepper Ost (RSO/3)
There is only one photograph currently available of a 15 cm sIG 33 (schweres Infanterie Geschütz 33), the standard German heavy infantry gun in WW2, loaded on the back of a Raupenschlepper Ost (RSO/3) tracked vehicle. The split trail legs can be seen sticking out the back of the vehicle. There had been no attempt to cut them to fit the length of the RSO/3’s wooden cargo bay.
This was not a test to see if the 15 cm sIG 33 howitzer could be fired from the back of the vehicle. The gun was too big and the RSO/3 would not have been able to handle the violent recoil. This vehicle was not a German Selbstfahrlafette Geschuetzwagen, a self-propelled artillery gun. It was almost assuredly a trial to see if the gun could be carried on the back of the RSO/3.
The experiment most likely failed, as the weight of the gun exceeded the designed load weight of the vehicle. The gun weighed 1,800 kg (4,000 lb) and the RSO’s load weight limit was 1.500 kg (3,307 lb). The RSO’s center of gravity would have been significantly raised. Both these things would have made the vehicle sluggish and difficult to maneuver. The RSO/3 was not a suitable vehicle to be a Waffenträger weapon carrier for the 15 cm sIG 33 howitzer.
The most plausible theory is that the Steyr-Daimler-Puch manufacturing company wanted to win a lucrative German government contract to build self-propelled artillery guns using their cheap to produce Raupenschlepper Ost light tracked vehicle and RSG. They exhibited four prototype vehicles that had different artillery howitzers mounted on the back to the government inspectors.
Two of the guns used were too big for the RSO tractor. The 7.5cm mountain howitzer was light enough and could be mounted to the floor of the wooden cargo bay at the rear of the RSO and RSG vehicles. These prototypes seemed viable as artillery SPGs.
At the time there was competition from other vehicle and arms manufacturers who wanted to win the same contract. Their designs used sturdier German tank chassis or captured enemy armored fighting vehicles on which to mount artillery guns. They won the contract, not Steyr-Daimler-Puch.
|Dimensions (L-W-H)||7.19 m x 3 m x 2.87 m
(14ft 6in x 6ft 6in x 8ft 6in)
|Total weight unladen||7,728 lb (3,505 kg)|
|Armament||7.5cm Gebirgsgeschütz 36|
|Track width||13 inch/24 inch with snow plates (33/61 cm)|
|RSO/1-2 Propulsion||3.5L Steyr V8 gasoline/petrol 70hp engine|
|RSO/3 Propulsion||Deutz F4L514 5.3L 4-cylinder air cooled diesel engine 66hp|
|Fording depth||34 inches|
|Top road speed||30 km/h (18 mph)|
|Operational range (road)||300 km (155 miles)|
One towed artillery gun required a team of six horses and nine men. WW2 German engineers came up with the idea of mounting an artillery gun on top of a tank chassis. This new technology reduced the amount of resources required to deploy one artillery gun. Artillery self-propelled guns only needed a four or five man crew. They could also be made ready to fire more quickly. This book covers the development and use of this new weapon between 1939 and 1945. One type was successfully used in the invasion of France in May 1940. More were used on the Eastern Front against Soviet forces from 1941 until the end of the war in 1945.