During the 1930s, the German Army wanted to introduce a new tank design to deal with fortified enemy positions. Two firms were contracted to develop and build a prototype, namely Krupp and Rheinmetall. While Krupp’s vehicle would serve as the basis of the later Panzer IV series, Rheinmetall’s version would not be so lucky. Whilst one prototype chassis was completed and tested by the German Army, it would ultimately be rejected.
Concept of a Support Tank
Following Germany’s defeat in the First World War, the Treaty of Versailles imposed severe restrictions on the size and capabilities of the German military, including limitations on the development of new weapons, such as tanks. Despite these restrictions, the German military began secretly developing tanks in violation of the Treaty. However, these efforts were initially limited due to a lack of funding and industrial capabilities. Additionally, tanks were a new concept at the time, and there was a lack of consensus on the best way to develop and employ them in combat. Nevertheless, German engineers and military leaders continued to work on them. In the mid-1930s, the Heereswaffenamt (HWa) (Eng. Army Weapons Department) issued a request for the development of two new types of tanks designed to fulfill specialized combat roles.
The first one was the Zugführerwagen or ZW (Eng. platoon commander’s vehicle). This vehicle, armed with a 3.7 cm KwK (short for ‘Kampfwagenkanone’, which can be translated as ‘combat vehicle cannon’ or, more simply, as ‘tank gun’) L/45 gun, was intended to spearhead an attack by German armored formations and deal with enemy armor. It would eventually evolve into the Panzer III series.
The second, known as the Begleitwagen BW (Eng: Escort vehicle), was intended as a fire support vehicle meant for the Panzer Regiments. Its purpose was to deal with enemy fortified positions, anti-tank and artillery emplacements, and similar targets by firing high-explosive ammunition. But before such a vehicle could be designed, the Germans had to resolve a few issues encountered during the testing of previous tank designs. In addition, a decision had to be made regarding the armament for this vehicle.
The new BW was also developed to act as a temporary substitute for self-propelled artillery, which the Germans lacked at that time.
In order to give the newly created Panzer divisions greater offensive capabilities, an artillery regiment was attached to them. This allowed the divisions to have their own dedicated artillery support to provide firepower against fortified enemy positions. Given that mobility was a key part of the Panzer division concept, these had to be mobile. To obtain the required mobility, the German forces employed half-tracks to transport and support the artillery guns, but they still needed time to properly set up for combat. Increasing the mobility of these guns while offering some level of protection could only be achieved in the form of self-propelled artillery. Even before the war, German Army officials were aware that such a vehicle was desirable. However, given the limitations of the German industry at that time, this was only a pipe dream.
Instead, BW tanks were to be used in this role too. For this, they would need a powerful gun. The 3.7 cm gun lacked sufficient destructive firepower. Another solution was to use a larger 7.5 cm caliber gun. Experience gained from the previous war showed that the smallest effective caliber for dealing with entrenched enemy positions was the 7.5 cm gun. But before a final decision was made, the German Army officials wanted to test the installation of an even larger caliber. In 1935, Krupp was instructed by Wa Prw 6 (the German Army’s Ordnance Department office responsible for designing tanks and other motorized vehicles, later renamed to Wa Prüf 6) to build a Panzer IV turret armed with a 10.5 cm L/16 gun.
The 10.5 cm gun was more powerful, but also heavier (plus the added weight of the larger rounds), requiring a stronger engine to compensate for the added weight. To ensure that the tank’s overall weight remained within project limits, the vehicle would have to have lighter armor. Consequently, the Germans determined that the 7.5 cm gun was a better solution, likely due to its more balanced weight and performance.
The next step would be solving the engine problem. Early German tank prototypes used adapted aircraft engines, which seemed cost-effective since no new development was required. However, these aircraft engines had a high torque and caused difficulties in the design of the drivetrain components. To handle the torque, the components needed to be robust and heavy, leading to increased weight in that area. Consequently, other components, such as armor, had to be made thinner to maintain weight limits. To address this issue, the Germans approached Maybach to develop a specialized engine designed specifically for tanks, which would likely offer better performance and reliability.
Lastly, the position of the rear drive sprocket was deemed ineffective because the tracks easily and too often fell off during testing. As a solution, the design was modified, and the drive sprocket was moved to the front, which improved track reliability and reduced the risk of the track falling off easily.
Once the overall design of the three components (armament, drive sprocket position, and engine) was determined, the German Army approached Rheinmetall and Krupp to request the design of a new 18-tonne tank. Rheinmetall was officially contracted in late February 1935 to provide a new chassis with a superstructure that incorporated a Maybach engine and a front-mounted drive sprocket. The design of the turret was to be handled separately, which was a common practice in early German tank development, with one company developing the chassis and another (often Krupp) designing the turret.
Before starting working on the BW project, Rheinmetall had fully designed (encompassing both the chassis and turret) the Neubaufahrzeug (Eng. new construction vehicle) or NbFz. Although the turret design would later be rejected, the chassis was considered adequate, and besides the soft-steel prototype, Rheinmetall built three additional chassis. Ultimately, the Germans quickly abandoned the concept of a multi-turret tank as they moved toward other tank designs and strategies.
Despite its cancellation, Rheinmetall engineers decided to reuse some of its components for the new BW project. This was a logical step to some extent, as it would speed up the development time and such components were already available. Unfortunately, the design history of this vehicle is quite poorly documented, with very little information available in the sources, other than the date the design was ordered.
Initially, this project was designated as verbesserten Nb.Fz. (Eng. improved new construction vehicle). It would be changed to Begleitwagen or simply BW (sometimes written as B.W.). Both of these unusual designations were used intentionally to deceive the Allies (the WWI victors), as the Germans were still technically forbidden from developing such vehicles. Sometimes, it is wrongly designated as VK20.01 (Rh). The real VK20.01 was another project initiated a few years after this project was officially ordered. For the sake of simplicity, this article will use the Rheinmetall BW designation.
The Rheinmetall BW chassis shared its general layout with other German tank designs of the time. The front part of the hull was dedicated to housing the transmission, followed by the crew compartment and the engine. This arrangement allowed for a fully enclosed front hull, providing protection to the crucial components located within.
However, in order to facilitate repairs and maintenance, two large hatches were positioned on the glacis to provide access to the transmission and steering systems. Additionally, there was a large plate bolted to the hull, likely serving as another inspection point for the transmission and a way to remove it for maintenance.
If this vehicle was introduced in this form, the inclusion of this large inspection plate and hatches could create potential weak points in the tank’s protection. This feature was common in early German tank designs, but it was later discarded in the development process. The decision to eliminate it was driven by the realization that it complicated production and created vulnerabilities in the tank’s armor. Overall, the inclusion of such inspection points and hatches in the early stages of tank development was a trade-off between the need for access to internal components for maintenance and the desire for enhanced protection. As tank design progressed, efforts were made to streamline production and improve armor protection, leading to the removal of unnecessary weak points.
The Rheinmetall BW utilized coil spring suspension, which was mostly carried over from the NbFz. On each side, there were four two-wheel bogies placed on pivoting arms (instead of five used on NbFz). These were cushioned with vertical coil springs. As requested, the drive sprocket was moved to the front, and an idler was placed at the rear. Lastly, there were three return rollers. To prevent mud from falling into the road wheels and potentially clogging them, a deflector guard was installed on both hull sides.
The Rheinmetall BW’s adjustable rear idler underwent some changes during the testing of its working prototype. In the original configuration of the prototype, there was an armored cover for the rear idler. However, at some point during the testing phase, this feature was removed. Unfortunately, without more specific details or additional context, it is challenging to provide further information about the changes made to the design of the adjustable rear idler.
This vehicle was powered by a Maybach HL 100 TR 300 hp@ 3,000 rpm engine. With a weight of around 18 tonnes, the maximum speed was reported to be 35 km/h. Other than the maximum speed, the vehicle’s overall drive performance is unknown.
The engine compartment was protected by extended parts of the superstructure. Noticeable features were the two hatches located on the top and the large protective ventilation port located to the rear of the engine complement. The engine exhaust mufflers were initially placed on the engine sides. These would be later moved to the rear of the engine compartment.
Rheinmetall’s engineers chose to deviate from the traditional box-shaped superstructure design commonly used by German tank designs at that time. Instead, they opted for a unique design that featured a hexagon shape (excluding the opening left for the auxiliary turret) when viewed from above, created by arranging flat plates. This design included two bulges that extended over the side fenders and covered the entire upper hull of the vehicle. This superstructure also extended into the engine compartment.
On the right side of the front superstructure, there was a larger opening specifically designed for the auxiliary turret. On the opposite side, the driver compartment was located. The driver compartment was fully enclosed and equipped with two observation ports, one at the front and one on the left side, and a hatch mounted on top. It is worth noting that, since the development of this vehicle never progressed beyond the prototype stage, there were no armored covers installed on the driver observation ports, as seen in the available photographs.
It is uncertain whether an observation port was added to the right side of the driver compartment. If such a port existed, its field of vision would likely have been restricted by the position of the auxiliary hull turret, making it unlikely to be placed there.
It appears that this prototype was never fitted with a working turret. There is a surviving photograph of the wooden mock-up which shows this vehicle being equipped with a turret similar, if not the same, as the later Panzer IV tanks. During testing, a round-shaped mock-up turret with three observation ports and a large opening to the rear was used. It was not a real turret and was used to simulate the weight of a fully functional turret.
Why Rheinmetall’s engineers included a secondary auxiliary turret is unclear. While the exact reasons behind this decision may not be explicitly documented, there are some speculations and observations that can shed light on this topic.
One possible reason is that they may have been influenced by their earlier NbFz tank, which featured two such turrets. These secondary turrets were designed to increase the vehicle’s field of fire and engage infantry, while the main turret focused on dealing with more substantial enemy threats. Although the Germans tested this concept, they ultimately abandoned it. It is worth noting that other European tank-building nations, such as the Soviet Union and the UK, utilized vehicles with secondary turrets in significant numbers.
Regarding the appearance of the secondary turret on the Rheinmetall BW, since there are no surviving photographs or detailed information available, it is purely speculative. Reusing components from the NbFz tank is a possibility, but without further evidence, it remains a hypothesis. These were similar in appearance to the turret used on the Panzer I, with some differences. The most obvious one was the use of only one machine gun. In addition, it employed a large angled machine gun mantlet not used on the Panzer I turret. They also had four observation ports. Lastly, one hatch acted as an entry point for the machine gun operator. It was protected by 13 mm of armor.
Based on the available information, the 7.5 cm KwK 37 L/24 gun was chosen as the main armament. Besides that, not much else is known about the armament. It is doubtful that the armament was ever tested with fully functioning capabilities. It is likely that the vehicle would have been equipped with additional machine guns for defensive purposes. One or two machine guns would have been mounted inside the auxiliary turret, providing a wide range of fire for the crew. One more machine gun would have been placed in a coaxial configuration with the main gun, allowing the gunner to fire it alongside the main gun.
Given that this project never went beyond the prototype stage, it was built using soft steel. Initially, it was planned for it to be protected with 13 to 20 mm of front armor. Besides that, nothing else is known about the armor thickness of the remaining components.
The vehicle would have featured a five-man crew, including a commander, gunner, loader, driver, and machine gun operator. The commander, gunner, and loader would have been positioned inside the turret, with the driver seated in the front of the hull and the machine gun operator in his sub turret.
Rheinmetall initially completed a wooden mock-up, which was then followed by a working prototype chassis in soft steel which was finalized by the end of 1935. While the working prototype chassis was presented to the German Army for testing and evaluation, there is no mention in surviving sources about what led the German Army to reject the vehicle. Several changes were made to the existing prototype vehicle during this time (such as the removal of the cover for the rear idler), implying that the German Army recommended changes during testing. However, without any surviving sources, all that is known is that Rheinmetall’s BW design was rejected in favor of Krupp’s design, which would evolve into the Panzer IV.
While it is not known for certain why the Rheinmetall BW was rejected, it can be theorized based on contemporary tank designs that did enter service that two main factors were disliked during testing. The first was the use of a suboptimal suspension system that was unlike anything else used by the German Army. This would likely have complicated maintenance on the vehicle were it to enter service. The second factor is the use of an auxiliary turret, which would have added unneeded complexity to the design and manufacturing process. In addition, such a turret might have limited the upgrade potential of the design should heavier or larger armament be required in the main turret, as was seen on later iterations of the Panzer IV.
Rheinmetall BW Technical specifications
|Crew||5 (driver, gunner, loader, and commander)|
|Engine||Maybach HL 100 TR 300 hp@ 3,000 rpm|
|Armament||one 7.5 cm L/24 gun and two or three machine gun|
T. Anderson (2021) Panzer IV, Osprey Publishing
D. Doyle (2005). German military Vehicles, Krause Publications.
P. Chamberlain and H. Doyle (1978) Encyclopedia of German Tanks of World War Two – Revised Edition, Arms and Armor press.
B. Perrett (2007) Panzerkampfwagen IV Medium Tank 1936-45, Osprey Publishing
T. Anderson (2017) History of the Panzerwaffe Volume 2 1942-1945. Osprey Publishing
T. Anderson (2015), The History Of The Panzerwaffe Volume 1 Osprey Publishing
T. L.Jentz and H. L. Doyle (1998) Panzer Tracts No.4 Panzerkampfwagen IV
K. Hjermstad (2000), Panzer IV Squadron/Signal Publication
Walter J. Spielberger (1993). Panzer IV and its Variants, Schiffer Publishing Ltd