The mittlerer Traktor (m.Tr., medium tractor), given the more widely known index Neubau Fahrzeug (Nb.Fz., newly designed vehicle) on October 3rd, 1933, began trials in 1933. The tank, an evolution of the Grosstraktor concept (Gr.Tr., large tractor) was supposed to become Germany's medium tank.
However, even as the tank began its trials, it was clear that the German military missed its mark. While the Grosstraktor was overcomplicated over its five years of development by three companies (it's enough to say that it was also amphibious), the Nb.Fz. was in an even bigger hole. The initial project, designed by Rheinmetall (chassis and turret) and Krupp (second turret variant) was supposed to fit into the 15 ton class. As a result, the appetite of the 6th Waffenampt led to a complex and expensive 23 ton tank.
A new tank concept split up tanks into support tanks and tank destroyers. The tank destroyer role was filled with the 10 ton Zugführerwagen (future PzIII). The Z.W. specification was developed in late 1933, even before the first Nb.Fz. was built. As for the Nb.Fz., it's fate was sealed in the fall of 1934. Initially, the new tank was called verbesserten Nb.Fz (improved Nb.Fz.) in documents, but a new index was used in correspondence between Krupp and the 6th Waffenampt starting on November 14th, 1936: B.W. or Begleitwagen, support vehicle.
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However, even as the tank began its trials, it was clear that the German military missed its mark. While the Grosstraktor was overcomplicated over its five years of development by three companies (it's enough to say that it was also amphibious), the Nb.Fz. was in an even bigger hole. The initial project, designed by Rheinmetall (chassis and turret) and Krupp (second turret variant) was supposed to fit into the 15 ton class. As a result, the appetite of the 6th Waffenampt led to a complex and expensive 23 ton tank.
A new tank concept split up tanks into support tanks and tank destroyers. The tank destroyer role was filled with the 10 ton Zugführerwagen (future PzIII). The Z.W. specification was developed in late 1933, even before the first Nb.Fz. was built. As for the Nb.Fz., it's fate was sealed in the fall of 1934. Initially, the new tank was called verbesserten Nb.Fz (improved Nb.Fz.) in documents, but a new index was used in correspondence between Krupp and the 6th Waffenampt starting on November 14th, 1936: B.W. or Begleitwagen, support vehicle.
Wooden model of the Rheinmetall B.W. This is how the tank was supposed to enter production.
It's worth noting that the Germans didn't invent anything new. The separation of tanks into tank destroyers and infantry support tanks is a British invention. In the 1920s, the Vickers company began building Medium Tanks Mk.I and Mk.II in two variants: with a 47 mm gun that fired only armour piercing shells and a 94 mm howitzer with only HE shells. The USSR also had experience with artillery support tanks (D-38, T-26-4, BT-7 Artillery). The T-28 was also an artillery support tank, in a way, but a longer gun was already in development when it was put into production. At that point, the only person to have put a long barreled gun into a medium tank was Eduard Grotte (TG-1), but his tank remained experimental. 37-47 mm guns were enough to fight tanks at the time, and short barreled guns and howitzers were better suited for fighting light fortifications.
For obvious reasons, the production of tanks that supported tank destroyers was planned in very limited numbers. The Germans were the only ones to design the tank from scratch. Other nations built a tank from an existing one. As a result, they ended up with two tanks by the end of the 1930s that had similar mass, armour, and an identical engine, but had completely different purposes. WHo knew that the highly specialized B.W. would outlive the tank it was supposed to support?
According to the initial plan, work on the Begleitwagen was split like with the Nb.Fz. Rheinmetall designed the chassis, Krupp designed the turret and turret platform. This separation of work was standard for German design. PzIII was a Daimler-Benz chassis with a Krupp turret and turret platform, the Tiger and Tiger II were Henschel chassis with Krupp turrets.
Rheinmetall signed contract 4167025/35 on February 25th, 1935, for a new tank that returned to the root of what the Nb.Fz. was supposed to be. It was supposed to weigh 17-18 tons. Its armament consisted of one short 75 mm gun with a coaxial machinegun, another machinegun would be placed in a cupola on the front of the hull, to the right of the driver. The crew consisted of six men: commander, driver, loader, cupola gunner, radio operator, driver.
B.W. experimental chassis, summer of 1938. The spaced armour covering the idler and the muffler on the fender are visible.
Rheinmetall reused many parts from their previous tank. The road wheels and return rollers, suspension, and track links were all from the Nb.Fz. On the other hand, the tank itself was completely original. A tighter layout with a transmission in the front allowed to shorten the hull by more than half a meter. The B.W. hull was also lower than that of the Nb.Fz.
The same vehicle after improvements. The suspension armour was altered.
A special Maybach HL 100 TR engine was used. This V-shaped 10 L 12 cylinder put out 300 hp, even more than its BMW Va aircraft predecessor. This engine was also planned for installation into the Z.W. The central and upper front plates had large hatches in them to make the ZF transmission easier to service, which didn't improve the tank's robustness.
Maybach HL 100 TR used on experimental Begleitwagen tanks.
The turret developed by Krupp had nothing in common with that of the Nb.Fz. One of the tasks given to the designers was maximum parts commonality with the Z.W. turret. The commander's cupola and side hatches were taken from the Z.W. turret, which was also designed by Krupp, and the overall shape of the turret was also similar. Initially, it was supposed to house a 21 caliber long 75 mm gun, but it was finally replaced with a 24 caliber gun, the same one used on the Nb.Fz. Contract #67941/35 for a new turret from mild steel was signed on January 3rd, 1936. It included the machinegun cupola, but that was never built. As for the main turret, it was finished in May of 1936.
The front of the improved Begleitwagen. The large transmission access hatches are visible. This solution made the transmission easier to service, but was not the greatest for shell resistance.
Initially, Rheinmetall was supposed to build two B.W. test chassis from mild steel, but only one was finished by May of 1936. It had neither a main turret nor a machinegun cupola, which were replaced with dummy weights. The exhaust system was altered during trials (the exhaust pipes were moved from the fenders to the rear), and the suspension and its armour were redesigned. All of these modifications were purely academic, since Krupp suddenly became the only participant in the Begleitwagen program on July 21st, 1936.
Even though Krupp was only supposed to work on the turret and turret platform, the arms giant from Hessen couldn't give up on such a juicy contract. Correspondence between Ritter, one of the conglomerate's executives, and the 6th Waffenampt hinted at Krupp's ability to supply more than the turret back in November of 1934. On April 13th, 1935, a month and a half after Rheinmetall began working on the B.W., Krupp proposed its own vision of the tank. The new tank had two variants, which differed in mass (17.2 and 18.5 tons), armour (14-20 mm and 20-30 mm), the amount of wheels (8 or 6 per side) and other details.
Krupp's onslaught was hard to resist, and finally contract #67096/36 was signed on July 13t, 1935, for one B.W. I Kp built from mild steel. On October 14th, 1935, a second contract #67252 was signed for a prototype of the B.W. II Kp. The difference between the two tanks was more subtle than initially proposed. In practice, the only difference was the suspension. The B.W. I used two-wheel bogeys with leaf springs, the B.W. II used three two-wheel bogeys with larger wheels and torsion bars.
B.W. I Kp at Krupp's assembly plant, summer of 1936.
Even though the work on the B.W. I Kp began much later than on the Rheinmetall prototype, the tank was ready on April 30th, 1936, a little earlier than its competitor. The tank was radically altered during assembly. A ball mounted machinegun from the Z.W. was used instead of a cupola. This solution reduced the crew from 6 men to 5, since the radio operator was now tasked with firing the machinegun. The first prototype took the test turret, and like Rheinmetall prototype, the second had to settle for a dummy weight.
Mobility trials began in the summer of 1936, and the first prototype traveled 2043 km by October 3rd. Various changes were made to the design during the trials, which is normal for a prototype. The first days of the trials showed that the 6th Waffenampt was right to let Krupp participate in the B.W. program. The tank achieved an average speed of 25 kph and moved more confidently than not only its competitor, but the Z.W, work on which stalled initially. The B.W. II Kp was not as fortunate. The torsion bar suspension design that Krupp selected was poor. These trials resulted in Krupp engineers becoming leery of torsion bar suspensions in general, even though the specific design they chose was at fault.
Externally, the first B.W. looks very similar to the PzIV Ausf. A. The similarity is misleading. The tank underwent significant changes, both on the inside and the outside, before it entered production.
A contract for the production of 35 1. Serie/B.W. tanks was signed in December of 1936, the tank was green-lit. However, the PzIV Ausf. A was significantly different from its predecessor. The hull and turret were radically changed, the engine and gearbox replaced, the suspension reworked. Nevertheless, the basis of the Begleitwagen concept allowed the production of a vehicle which was never radically altered during production.
The same cannot be said about the PzIII, the first four modifications of which were more like a search for good technical solutions. In practice, the first proper PzIII was the Z.W.38, or PzIII Ausf. E. Even it could not achieve the desired qualities (for example, the 70 kph top speed that bothers the minds of many military history enthusiasts was only attainable for a short time before the suspension fell apart), but at least an acceptable suspension was found. MAN was included in the production of the PzIII Ausf. E, but even put together with Daimler Benz they could only produce 96 tanks. By September 1st, 1939, only 196 PzIII tanks were built. This tank was considered the main tank, even though there were 217 PzIV support tanks built by then.
As for the prototypes, the first tank was sent to a training facility in Metzingen in December of 1936. The second prototype served as a testbed for a new turret platform in the spring of 1938, which later was used on the PzIV Ausf. B (the machinegun was replaced with a pistol port and the "step" in the upper front plate was removed). The B.W. I Kp turret was installed on the second prototype in April of 1938, and remained there until at least November. In 1939, the B.W. II Kp was converted into a bridgelayer. As for the first prototype, it was also involved in more trials. A new suspension was tested in the winter of 1939-40.
B.W. II Kp converted into a bridgelayer, 1939.
In conclusion, it's worth mentioning that Krupp developed another very interesting tank on this chassis, the Rauchwagen (R.W.), or smoke vehicle. This was the same B.W., but with a 105 mm L/16 howitzer in the turret. This tank was first brought up in 1935, while the B.W. was still in development. In addition to the ability to put up smokescreens, the gun could have had superior penetration, as the 7.5 KwK L/24 could only penetrate 25 mm of armour at 700 meters, while French tanks had 40 mm of armour.
According to correspondence, the project reached the practical phase. The first B.W. turret removed from the B.W. I Kp was sent to Krupp in the winter of 1938, and conversion to the new weapon began. In April of 1938, the turret was installed on the B.W. II Kp, which received the PzIV Ausf. B turret platform. According to a report dated November 17th, 1938, the turret was removed from the B.W. II Kp and mounted on a special stand for trials; the tank was sent to be converted to a bridgelayer. This was the end of the "smoke vehicle". The last time it was mentioned was in September of 1939.