Sunday, 26 June 2016

Krupp Leichttraktor: Rival with no Future

During the First World War, a special technical commission presided over all German tank development, headed by General Friedrichs. The commission appointed a captain from the automobile forces, Joseph Vollmer, to direct design work. When Germany lost the ability to develop and produce tanks after the war, a part of their engineers left the country and began building tanks for other nations. However, several years later, work on new vehicles resumed, and companies who were left during WWI had their chance. The Krupp conglomerate was one of those companies.

LK.II Reimagined

Founded in Hessen in the early 19th century, the Krupp steel casting company turned into a manufacturing giant by the end of the century. Its armament, especially cannons, quickly became one of the most important products of the quickly growing company. By the start of WWI, 140,000 people were working for Krupp in Hessen. This was a true manufacturing army, capable of supplying the Kaiser with a weapon of any caliber, in any numbers.

Naturally, Krupp couldn't walk by such a promising novelty as tanks. The German A7V was built with hulls built, in part, in Hessen. It is expected that Krupp would wish to build its own tanks in house. This possibility arose when work on the LK (Leichter Kampfwagen) light tank began in 1917. Krupp united its efforts with Daimler and challenged Captain Vollmer.

Even though the forces were anything but equal, Krupp didn't achieve victory. The Kleiner Sturmwagen developed by Krupp and Daimler turned out to be worse than its competitor. The alliance of two manufacturing giants designed more of an armoured tractor than a tank, and one with questionable characteristics at that. Vollmer's concept with a front engine and rear fighting compartment seemed a lot more viable. Of course, the victory was a brief one, as the German army never received any LK.IIs.

Illustration from Georg Hagelloch's patent, one of the few known images of the Kleiner Sturmwagen. The modernized tank would have this suspension. Some solutions from this project carried over to the Kleinetraktor.

German arms manufacturers sat quietly for the first half of the 1920s, suppressed by Versailles restrictions and the economic downturn. Without a possibility of working in Germany, Vollmer left for Czechoslovakia, working on convertible drive tanks there. Meanwhile, in 1925, Germany took a few shy steps towards developing tanks once more. Krupp took part once again. Initially, the idea was to develop SPGs on existing tractor chassis.

The first known materials on the tank called Kleinetraktor for secrecy are dated March 1928. It's likely that work began long before, as by that point, two years of work have been done on another vehicle, initially called Armeewagen 20. Work on this 15 ton vehicle was done on a tender system, with Daimler-Benz and Rheinmetall competing against Krupp. These tanks would become the backbone of the German tank forces in the future. However, it quickly became obvious that the vehicle would be complex and expensive, and the short 75 mm gun was not the best choice for anti-tank work. Another tank was needed: smaller, simpler, cheaper, without any excesses such as amphibious capability. History repeated itself: after the heavy A7V, the LK had to be designed.

Illustration from patent DE514219C by Erich Wolfert. The patent was filed on June 21st, 1929, meaning that the real idea could be several years older. Don't let the word "tractor" fool you, this is a transmission and control system for the Kleinetraktor.

The design of the Kleinetraktor concept was done jointly by Krupp and the 6th Waffenampt, qhich was responsible for armoured vehicles. Erich Wolfert was in charge of efforts from Krupp's side. This engineer was one of the key figures in Krupp's armoured vehicles department. Georg Hagelloch, the man who designed the suspension of the Kleiner Sturmwagen, was another. These two would go on to develop the suspension for the B.W. (future PzIV). Heinrich Kniepkamp, another future pillar of the German tank school, represented the 6th Waffenampt in this matter.

Initial requirements formulated by the 6th Waffenampt described a 6 ton vehicle with a 60 hp engine with a top speed of 40 kph. It was quite naive to expect such a high speed from a vehicle with only 10 hp/ton of power. Even the PzI Ausf. A, with a much better suspension and weighing only 5.4 tons, could not achieve a speed of over 37 kph. In this case, we're talking about the late 1920s when the search for a good suspension design was just starting. German engineers had some hopes about rubber-metallic tracks. This invention was borrowed from the Renault FT-Kegresse, where it increased both the top speed and range of the tank.

Krupp Leichttraktor when it was first built, spring of 1930.

Conceptually, the Kleinetraktor would have been an LK.II, but smaller. The first tank was planned for 1929, and mass production would start in 1931, with an initial batch of 17 tanks costing 50,000 marks each. Krupp would be the manufacturer, and it was tasked with building two experimental prototypes. However, by May 8th, 1929, it became obvious that the requirements are a little detached from reality. The 60 hp engine was not enough for the required speed.

On May 26th, a meeting was held between Wolfert, Hagelloch, and representatives of the 6th Waffenampt to set the characteristics of the tank. Its armour thickness was set at 14 mm, which would protect it from rifle caliber bullets at any range. The mass of 6 tons was approved, and a 37 mm Rheinmetall gun would be used as the armament. A radio and a smoke device were included in every tank. The tank also changed its name. Another project was titled Kleinetraktor, and the existing vehicle was named Leichttraktor. 

Brief Leadership

Another important decision was made at that meeting. Krupp's monopoly over the Leichttraktor ended. Two more companies were included into the tender: Rheinmetall and Daimler-Benz. The Rheinmetall design is covered in a separate article, so we won't dwell on it.

As for Daimler-Benz, it did not pay much attention to the Leichttraktor program. All participants were tasked with building two prototypes from mild steel, but Daimler-Benz did not even reach the draft stage. Loaded with the Armeewagen 20, renamed on March 14th, 1928, to Grosstraktor, the company left the program in July. However, some participation was still necessary. The Daimler-Benz M36 7.8 L 100 hp engine was the most suitable for the future tank. A Maybach engine was an alternative, but it was 40 kg heavier and took up more space.

The exhaust pipe is elevated as high as possible. It's unlikely that the radio operator would have liked this solution.

On July 3rd, 1928, the M36 was set as the engine of the Leichttraktor, paired with the gearbox from the Krupp 3 ton truck. The engine was positioned in the front of the tank, then a driveshaft connected it to the transmission and drive sprockets in the rear. According to initial specifications, the Leichttraktor would be 3900 mm long, 1850 mm wide, and 2000 mm tall. The mass was still set at 6 tons.

This tank was smaller than the Renault FT, and only the Light Tank T1 with a similar layout was smaller. The American tank could have influenced the design of the Leichttraktor, as advertisements for the new tank already appeared by summer of 1928, during the peak of activity of the Leichttraktor project. A more significant influence can be seen from the Medium Tanks Mk.I and Mk.II, which appeared even earlier.

With these small dimensions, the Leichttraktor had a respectable crew of 4. It included a driver and a radio operator sitting in the hull, with a gunner and commander (doubling as a loader) in the turret.

The name Leichttraktor had a grain of truth to it. The idea of a commercial L.Z. (leichte Zugmachine) tractor with a 60 hp engine was seriously considered. The idea was quickly dropped, but Krupp installed a cabin and a truck bed on its chassis instead of a turret and turret platform. An ammunition carrier on this chassis had a similar design (without a turret or turret platform). According to existing documents, it was also built. A box-like addition turned the tank into a forward observer vehicle, similar to the British Medium Mk.II Box Tank. Finally, the Leichttraktor was considered as a base for an SPG.

The design of the front of the tank prompts many questions, especially about the air intake grille.

Requirements for the vehicle changed constantly. In late July of 1928, realizing the excessive optimism about the tank's speed, the requirements were decreased to 35 kph. In October, the cooling system was redesigned. Around this time, a wooden model of the tank was presented.

Finally, in late October, a contract was signed with Krupp about the production of two prototypes. The overall cost of the project was 230,000 marks. Unlike Rheinmetall, there was no contract to build an SPG. Perhaps the German military already suspected something.

1929 was spent on design work and preparation for building an experimental vehicle. Finally, in early 1930, the chassis of the tank called Kp.L.Tr. in some documents was demonstrated to representatives from the 6th Waffenampt. The vehicle confidently drove over mud, and the military appeared impressed. Krupp estimated that the assembly of the first tank could be finished by April 1st, and the second by May 1st. That estimate was spot on: work finished on April 26th.

A careful examination of the vehicle, especially a thorough comparison with the Rheinmetall design, raises a lot of questions.

A large rear hatch allowed the crew to leave the tank without using any other hatches.

Neither Krupp nor Rheinmetall managed to meet the weight requirements. The tank turned out to be 20 cm longer, 13 cm taller, and 20 cm wider than required. The mass was 7900 kg, or a third higher than requested. It's no wonder that the real top speed did not go past 30 kph. While Rheinmetall's tank was both longer and heavier, its hull design was one of the best among front-engined tanks of the time.

It's hard to say the same about the Kr.L.Tr. One glance was enough to figure that out. Even though the hull was welded, this progressive solution was nullified by several design choices. Krupp's light tank was closer to a WWI era vehicle.

Several decisions made by Krupp make one think that their design was a tractor all along, only covered by armour at the last minute. The armoured radiator grille was designed in such a way that bullets could reliably ricochet inside the hull. However, this was nothing compared to the radiator's fill opening, which was completely unprotected.

The tank's crew no doubt had many strong words to say about the engineers who designed the engine compartment roof. It had a very complicated shape, and had to be entirely removed before the engine could be serviced. The driver's hatch also looked questionable, resembling a helmet of a Teutonic knight. It was impossible to climb out of, and another hatch on the side of the hull was meant for exiting the tank. It is doubtful that it was ever used, as the rear hatch seemed much more promising.

The front of the tank without the armour or radiator.

The suspension also posed a lot of questions. It consisted of 13 road wheels and 2 return rollers per side. One road wheel was responsible for absorbing shock when the tank hit an obstacle. The other wheels were coupled into a complicated system of bogeys, supported by only one leaf spring. It is not known why Krupp engineers decided to create such a mystifying design, but maintenance of it would have no doubt been even more memorable than maintenance of the engine. The overall picture was completed by the side skirts. No small hatches that could ease the crew's work were present here. If something went wrong with the suspension, the armour had to be removed completely.

It is easier to show the suspension once than attempt to describe it.

The only thing that no complaints could be made about was the turret. Both tanks had turrets designed by Krupp, but produced by Rheinmetall. The design could easily be called one of the most progressive of the time. Mysteriously enough, its designers omitted any hatches on top. The turret ring diameter was truly stunning for the time: 1400 mm. The turret was conical, with observation devices in the roof. Another novelty was the collection of all armament behind one gun mantlet. Even though the Americans invented coaxial armament before this, the German tank was the first where it took its modern shape.

It was strange to see such a progressive turret on such a confusing chassis. No one could hope for victory over Rheinmetall, and trials confirmed those fears.

Trials in the USSR

On May 7th, 1930, both Kp.L.Tr. indexed 37 and 38 were sent to the proving grounds at Kazan. It is often called KaMa, but the real name was TEKO (Technical Courses at OSOAviaHim, the Society of Cooperation with Defense, Aircraft, and Chemical Industry). Tanks were tested here, and German tankers trained. On one hand, the Germans had a chance to test their vehicles away from prying eyes. On the other hand, Soviet engineers had access to German designs. Testing German tanks in the USSR benefited the Soviets more than the Germans.

In 1930, tank #37 traveled 365 km, and tank #38 534 km. In the first few months it became obvious that Krupp's tanks need a serious redesign. Aside from the radiators, which had to be reinforced, the suspension gave a lot of trouble. The drive sprockets had to be replaced by the end of July. The suspension and its one leaf spring per side also misbehaved. The rubber-metallic tracks did not prove themselves. The situation was so grim that Hagelloch himself visited TEKO in October of 1930.

The only known image of a Kp.L.Tr. with a second type of suspension.

Having studied the problem, Krupp engineers began developing a new suspension. The rubber-metallic tracks were discarded, as they were clearly unsuitable for tanks. Everything from the old suspension was thrown out aside from the idlers and their mounts. The munitions carrier, which was left in Germany, was used as a test lab for the new suspension.

Krupp engineers did not seek any easy solutions. The amount of wheels per side was reduced to eight, of three different sizes. The frontmost wheel was the largest, and the rearmost wheel the smallest. To improve robustness, the six middle wheels were connected by a beam. One odd design was replaced with another. Instead of the inadequate drive sprocket, a new one with a removable crown was used. The tank also gained fully metallic tracks.

The tank with a modified version of the second suspension. Springs are already used, the driver's hatch replaced, and fenders installed.

The first work on a new suspension started in December of 1930. In parallel, a more reliable transmission was designed. As new elements were tested, they were sent to the USSR for installation. Around this time, the Kp.L.Tr. received fenders, as the tracks would throw mud in every direction during operation.

The new suspension also proved problematic, and reports about one breakdown or another were constantly sent to Germany. The idlers were eventually changed, as their design proved poor. However, the design of the tank had flaws that could not be solved with any modernization. In a report on September 10th, 1931, it was stated that the front engine tired out the driver and was not a good solution.

The air intake grille was changed in the final configuration.

As a result of trials, the suspension was again redesigned, increasing the number of wheels per side to 9. Other elements of the suspension were also changed. The length of the tank increased to 4295 mm, and the mass was expected to increase to 8.4 tons. The new suspension was successfully tested on the munitions carrier in January of 1932. By that point, tank #37 traveled 697 km and tank #38 traveled 371. During the spring and summer of 1932, the lengthened suspension was tested at TEKO, where tank #37 traveled 598 km and tank #38 traveled 1095 km.

In the summer, the tanks returned to Germany for major repairs. At least one received a new radiator grille, and tank #38 received a new antenna. The driver's hatch was changed. In December of 1932, it was decided that vertical springs would be used in the suspension instead of leaf springs, 4 per side, although this solution was implemented much later. The modernization didn't help much, as the design was still rather archaic.

The final configuration of the Kp.L.Tr.

Even though the tank continued trials until the end of 1934, its fate was decided sooner. On January 27th, 1934, the 6th Waffenampt decided to begin work on a new 10 ton tank, the Z.W. (future PzKpfw III). This buried the previous projects. However, the Kp.L.Tr. managed to serve the Wehrmacht. During exercises in 1935, one Krupp Leichttraktor served as an observer vehicle, with a casemate installed instead of a turret. The tanks were used as training vehicles for some time. Very soon, they became monuments.

Kp.L.Tr. on a monument, a fitting end to its story.

The end of the Kp.L.Tr. is predictable, but it's hard to call the Leichttraktor project a failure. Many tanks of the late 1920s suffered the same fate. Only the Soviet MS-1 entered real mass production. Even the Vickers Mk.E, a progressive and successful tank, only achieved fame abroad.

The Leichttraktor, despite its great secrecy, left its mark on world tank building. Its turret influenced other tank building schools. This is especially noticeable in Swedish tanks. The turret of the Lansdverk L-10 is effectively a reworked Leichttraktor turret. The same can be said for many Swedish vehicles of the 1930s. Considering that Landsverk was under German control, this is not surprising. The turret of the Polish 7TP also has several features characteristic of the Leichttraktor turret.

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