Monday, 24 July 2023

Between the Pz.Kpfw.III and the Panther

 German medium tanks that could not replace the Pz.Kpfw.III or IV

One might think that tank building developed very sluggishly in the interwar years. This is a mistake. Development continued even in the most difficult years when there was no money for tanks. Every 3-4 years tactical-technical requirements were revised and development of new prototypes began. Germany did not differ from the rest of the world in this regard. Since Germany was bound by the terms of the Treaty of Versailles, this cycle was concealed, but the mask was dropped in the early 1930s even before the Nazis came to power. This is when the tanks that Germany entered the war with began to form.

A broken Pz.Kpfw.III Ausf.F. Frequent gearbox failures were the reason why production of the Z.W.38 fell behind schedule and the relationship between Daimler-Benz and Heinrich Kniepkamp was ruined.

There are many cases in tank building where a nation manages to catch one wave of trends and miss the next. The USSR managed to create a successful series of tanks in the early 1930s but failed to do so in the mid-30s. On the other hand, German tanks developed in the early 30s were failures, but the designers redeemed themselves a few years later. Subsequently, while the USSR got the successful T-40, T-34, and KV-1 at the end of 1939, the Germans entered the new decade with a completely different result. One example is the story of the tanks that was supposed to replace the Pz.Kpfw.III and the Pz.Kpfw.IV: the VK 20.01 and its relatives.

VK 20.01 (D). Instead of a torsion bar suspension, it used a clever layout with leaf springs.

The cause for the appearance of these tanks was clear. The Zugführerwagen (platoon commander's vehicle), also known as the Pz.Kpfw.III, was a very problematic vehicle. Production until the end of the 1930s took place in small batches of 10-15 experimental tanks. This was hardly satisfactory for German commanders. It was already clear that medium tanks will be the main force on the battlefield, but their main medium tank was still very raw. There was also the Begleitwagen (support tank) or Pz.Kpfw.IV, but it was considered a temporary measure. The 6th Department of the Weapons Office tried to ignore the fact that the B.W.(Kp) was an obviously more successful vehicle from the start. Daimler-Benz, the developers of the Z.W., began to suspect something. They built tanks to requirements of the 6th Department, but began to lose patience by 1938. It was clear that the torsion bar suspension they were forced to use could not support the required speed for long. The 10-speed semiautomatic Maybach Variorex 328 145 gearbox also had a ton of issues.

VK 20.01 (D) on trials.

Despite all this, no one thought of cancelling the Z.W.38 or Pz.Kpfw.III Ausf.E. Preparations for production at Daimler-Benz and MAN were already underway. However, the issues with the suspension led to the 6th Department (or rather Heinrich Kniepkamp, who took charge of almost all tank development) starting work on a new tank designated VK 20.01 (III). Daimler-Benz developed the chassis and Krupp developed the turret. Initially, the turret was supposed to be the same as on the Z.W.38. The chassis was much more interesting. Kniepkamp clearly transplanted the same solutions that were used on the D.W., the unsuccessful heavy tank that evolved into the VK 30.01 (H). The technical specifics of the VK 20.01 (III) are almost unknown, but it was going to have new running gear with large interleaved road wheels and a torsion bar suspension. Return rollers were omitted. The draft of the VK 20.01 (III) dated December 15th, 1938, used the 16 L Maybach HL 116 engine that put out 300 hp at 3000 RPM. The same engine was used on the VK 30.01 (H). Judging by similar projects, the transmission would have also come from the VK 30.01 (H). 

This was the first German tank with a diesel engine.

Kniepkamp's plan may have worked, but the Z.W.38 was the last straw for Daimler-Benz. Issues with the Maybach Variorex 328 145 led to an outright failure of Z.W.38 production. The start of the war was accompanied with loud complaints from the army. The industrial giant's patience wore thin and in October of 1939 Daimler-Benz received permission to begin developing tanks independently. The Tank Commission led by Ferdinand Porsche also did not come into being out of nothing. Kniepkamp held on to his position, but Daimler-Benz wriggled out of his grasp. On November 15th, 1939, DB presented a project called GBK (Kampfwagen des Generalbevollmächtigten). Instead of a semiautomatic gearbox, it used a Praga-Wilson type planetary gearbox copied from the LT vz.38. Another alternative was the same ZF SSG 77 gearbox used on the "corrected" Pz.Kpfw.III. The engine was no less interesting. Instead of the Maybach HL 116 engine, the GBK used a 315 L water cooled MB 809 diesel. Finally, a complex system of leaf springs replaced the torsion bar suspension.

The first tank designated B.W.40.

It would appear that the complaints began much earlier than that, since a chassis to potentially replace the Pz.Kpfw.IV tank was discussed at the 6th Department on September 15th, 1939. This was quite an odd discussion, since a few years earlier Kniepkamp fought to destroy the B.W. entirely. The engine and likely transmission would have come from the VK 20.01 (III), but the running gear was typical for Krupp: bogeys with leaf springs, quite similar to those used on the Pz.Sfl.IVb, but with 630 mm road wheels. The speed was limited to 42 kph. The tank was initially indexed VK 20.01 (IV), but in November of 1939 it changed to VK 20.01 (BW) and then in December to the better known B.W.40. The front of the hull was also thickened from 30 to 50 mm. As for the Z.W.38's replacement, Krupp found someone to take over for Daimler-Benz. This was MAN, a company that managed to steal light tank production from Krupp without a lot of noise.

VK 20.01 (K). Krupp was pressured to develop this tank by the 6th Department of the Weapons Office.

MAN's design bureau headed by Paul Wiebicke began working on its own tank named VK 20.01 (M). The tank was clearly designed using prior experience of the 6th Department in mind. Kniepkamp continued to revive questionable parts of the VK 30.01 (H). For example, the 8-speed ZF SMG 91 semiautomatic gearbox was recommended for the VK 20.01 (M). The VK 30.01 (H) used the SMG 90 gearbox. The torsion bar suspension with interleaved road wheels was a given, except for one curious exception: there was no room for the front and rearmost torsion bars, so those suspension arms had a coil spring. The first designs were finished by October 10th, 1940. The development was coloured by another event. On May 16th, 1940, Krupp was informed by the 6th Department that the B.W.40 was cancelled. The explanation given was "difficult situation on the front lines". In reality, the tank was cancelled because it deviated too far from Kniepkamp's ideas. This kind of mandatory compliance is also why the VK 20.01 (K) was designed with a torsion bar suspension.

VK 20.01 (M), the favoured design of the 6th Department.

There were three pretenders to the throne of the Z.W.38 by the start of 1941: two "legitimate" ones from MAN and Krupp and an outsider from Daimler-Benz. It seemed that MAN and Krupp's tanks would have a higher chance of success, but it was not so simple. Daimler-Benz had their own very powerful engine supply chain as well as significant tank building experience. Of course, their suspension was outright poor, since it took up a lot of space and service would have been a headache. Nevertheless, the first MB 809 engine was started in February of 1941 and a month later it was installed in a VK 20.01 (D) prototype with serial number 30009. The serial number should not be surprising, as it was only one of a series of experimental vehicles. It is often said that only one chassis was built, but photos from 1945 show two.

The final configuration of the VK 20 tanks would have had a 50 mm KwK 39 L/60 gun.

Work on the tanks continued at a rapid pace. Krupp received an order for a turret in late 1940, initially with the requirement to fit the 50 mm KwK 38 L/42 gun. The turret had 50 mm of front armour and 30 mm of side armour. There is no detailed information on this turret, but it's shown in the VK 20.01 (M) diagram. Krupp and MAN also received an order for 12 pilot tanks in addition to prototypes. The 50 mm KwK 39 L/60 appeared in March of 1941, although its arrival changed little. The VK 20.01 (K) also evolved into the heavier VK 23.01 (K). All this development never left paper. As for the VK 20.01 (D), it continued to rack up mileage. The 22.25 ton tank reached a speed of 50 kph. Despite the poor suspension, the chassis was quite good and had a reserve of weight. The VK 20.01 (D) had 440 mm wide tracks and a decent ground pressure. This came in handy during winter trials.

VK 24.01 (M), the last attempt at saving the 20 ton tank.

The situation did not change much by the fall of 1941 MAN reported that the chassis is ready, but is awaiting transmission elements. Their designers continued to polish the VK 23.01 (K) and other variants of the tank, pessimistically pointing to one or another reason for delays. The VK 20.01 (D) was a clear leader, despite Kniepkamp's protests. Ironically, production of the Pz.Kpfw.III Ausf.J began in the spring of 1941. It had the same armour and received the 5 cm KwK 39 L/60 by the end of the year. Compared to this tank, the 20 ton series did not look like a step forward. Finally, the Tank Commission along with Ferdinand Porsche visited Mtsensk on November 18th, 1941. A review of the KV-1 and T-34 resulted in a pessimistic evaluation: even Germany's prospective tanks were obsolete.

Two VK 20.01 (D) test chassis (indicated by arrows) and a VK 30.01 (D), 1945.

The VK 24.01 (M) was the last attempt to rescue the VK 20. This name was given to a 24 ton tank with sloped armour presented by MAN on November 25th, 1941. This variant did not live for long. The 20 ton tank class vanished by the end of December. In this time, the first German tank chassis to carry a tank engine had travelled for 6163 km. This story with 20 ton tanks is infrequently remembered, which is a shame. These tanks were a part of the same wave as the T-34 or Medium Tank M4, but some of the projects were successful and some not. The next wave was the opposite. The T-43 and Medium Tanks T20/T22/23 were not successful while the German Panther did a lot better.

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