Saturday, 25 June 2016

Rheinmetall's Fighting Tractor

German tanks of the first half of the 20th century are commonly associated with Tigers and Panthers, light and medium "Panzers" designed in the 1930s, and the first German tank, the A7V. Meanwhile, the work of German tank designers in the 1920s remains in obscurity, although many interesting designs were developed during that time. For various reasons, German designers were forced to work abroad. Nevertheless, secret work on domestic tanks began in Germany in the late 1920s. One of those tanks was the Leichttraktor.

Small and Smaller

According to the Treaty of Versailles, Germany was forbidden from developing and producing armament and military vehicles, including tanks. Engineers in that field left Germany and began working in other countries. This explains why German tank design skipped over the various cadavers that were built in other countries. German engineers worked on these dead end designs while foreign money paid for it. Nevertheless, this could not continue forever, and sooner or later, work had to start in Germany.

The first signs of a German tank building revival appeared in 1925. Naturally, all work was done in strictest secrecy. A year later, self propelled gun mounts on the chassis of commercial tractors began development. Development of the Armeewagen 20 also started around this time, a medium tank that evolved into the Grosstraktor on March 14th, 1928. The vehicle was conceptually new and had no foreign analogues, even though it somewhat resembled a shrunken down FCM 2C. The new tank would achieve a speed of 40 kph, which gave it high mobility on the battlefield.
Factory diagram of a Rheinmetall Leichttraktor.

One "large tractor" was not enough. Its armament, a short 75 mm gun, meant that its enemy was going to be infantry and light fortifications. The same function was performed by the British Medium Tank Mk.I CS and Medium Tank Mk.II CS. This is where the Germans copied their howitzer tank concept from. Meanwhile, most British tanks had 47 mm guns, which could perform in an anti-tank role. It was logical that the Germans would develop tanks other than medium tanks.

Alas, the earliest available documents on the topic are dated March 1928, even though development clearly began earlier. Initially, this tank was labelled Kleinetraktor (small tractor). In this case, it was not only a codename, but one of the three functions of the vehicle. Aside from a tank, the Kleintraktor could function as an artillery tractor, towing a 37 mm Tak gun or 77 mm FK 96 n.A. field gun. According to motorization plans approved on April 17th, 1928, the first finished Kleintraktor was scheduled for October of 1929. Trials would be performed in 1930 and 17 tanks would be built costing 50,000 marks each.

The conceptual designs were  performed by Krupp and the 6th Waffenampt, responsible for development of armoured vehicles, in the spring of 1928. The initial design was of a two-man fighting vehicle with a 60 hp truck engine. With it, the speed of the tank would reach 40 kph. Although, by late April, it was obvious that the engine would be too weak for the Kleinetraktor. The growing appetites of the military pushed the tank out of its original vision.

The chassis was built first, and a turret platform and turret were installed later. In this form, the vehicle could very well have been called a tractor.

A meeting was held on May 26th, 1928, with representatives from Krupp and the 6th Waffenampt. Since the Kleinetraktor was getting out of hand, a decision was made to split up the project. The designation Kleinetraktor would be used for a 3 ton vehicle, and the current project was renamed Leichttraktor (light tractor), or L.Tr. for short. According to the approved specifications, the mass of the tank would be 6 tons and the crew would consist of 3 people. The maximum speed would be 40 kph on a highway and 20 kph off-road. The main armament would be the 37 mm Tak gun, installed in a turret developed by Krupp. The tank would also be equipped with a smoke launcher and a radio.

Paper Panzers

Like the Grosstraktor, Krupp did not have a monopoly on the Leichttraktor. After designing the overall concept, contracts would be signed with several companies and a superior design would be selected. Rheinmetall and Daimler-Benz were involved in parallel. Daimler-Benz did not actively participate, as the Grosstraktor was enough for them. However, it was still drawn into the project, as Krupp was leaning towards using their 100 hp M.36 engine. There was a Maybach competitor, but it was larger.

The initial design of the Rheinmetall Leichttraktor.

The Leichttraktor began taking its final form in early June of 1928. Krupp's brainchild resembled both the British Medium Tanks Mk.I and Mk.II and the German light LK.II tank. The resemblance to the latter was rather superficial; the British influence was much more prominent. Like the British tank, the Leichttraktor had a front engine, with the driver shifted to the left. Hatches on the side and a large rear hatch extended the resemblance (although to be fair, the latter was introduced later in the design process).

The turret was placed in the rear. The crew was increased to 4, now including a radio operator that sat to the right of the driver. Krupp's engineers designed a suspension with a large number of road wheels. Removable skirt armour was used to protect it from enemy fire.

The tracks had French ancestry. Krupp (or rather Heinrich Kniepkamp, who was already actively working for the 6th Waffenampt) made rubber-metallic tracks based on the ones from the Renault FT-Kegresse. The Germans ended up with a rather convoluted design involving two strips of fanged rubber with rubber-plated metallic inserts.

Leichttraktor from the front with hatches open.

Like the Kleinetraktor, the Leichttraktor was designed with other military uses in mind. A turretless variant could be used as an ammunition carrier. A forward observer vehicle, an artillery tractor, and an SPG were also designed.

It turned out that the 75 mm gun that was planned for use instead of the FK 96 n.A. was too large for the small fighting compartment, and that design was dropped. The only gun for the tank would be te 3.7 cm Tak. A commercial tractor on this chassis was also planned, but that design was dropped eventually too.

Large hatches in the hull and turret let the crew comfortably enter the tank and quickly leave it.

Changes kept being made to the project. Even though the tank's mass still remained under 6 tons, its top speed was decreased to 35 kph. Even though there were no requirements to make the tank amphibious like the Grosstraktor, that idea was kept in reserve.

The protection of the tank took a strange turn. Initially, the radiators were going to be positioned as flat as possible, but orders were given from the top in October to put them in front of the engine. As a result, the air intake was in the most vulnerable place, even though it was covered with a grille. Large changes to the project stopped only by the end of fall of 1928 when the models were already being built.

Competitor from Dusseldorf

As mentioned above, Daimler-Benz had little interest in the Leichttraktor project, and in July of 1928, the company officially declined a bid. Only two competitors remained. The story of the Krupp Leichttraktor is a long one and deserves a separate article. Here, we will talk about the Rheinmetall design. Like Krupp, it signed a contract in October of 1928 to build two Leichttraktor prototypes. In addition, Rheinmetall earned the contract to build the turrets, not only for their own tanks, but for ones built by Krupp as well. Rheinmetall's tanks were numbered 39 and 40.

Rheinmetall Leichttraktor Selbstfahrlafette. Note that the difference from the base vehicle is minimal.

The Rheinmetall design was much better than the Krupp one. Despite identical requirements, Rheinmetall ended up with a slightly different kind of tank. Its mass was 8 tons, 100 kg heavier than its competitor. It was also 70 mm shorter, 35 mm lower, and 32 mm wider. The hull was rather laconic in shape, with a large slope in the front. The grille in the front didn't help with protection, but there was nothing to be done when the design was pushed through from the top. To be fair, the same problems existed with the American T1 Light Tank and British Medium Tanks Mk.I and Mk.II.

The attention paid by the designers of the Rheinmetall Leichttraktor (also designated Rh.L.Tr. in documents) to the convenience is obvious. Thanks to a hinged engine compartment roof, it was easy to access the engine and radiators. The grille was also removable, which made it easier to service. The tank was the first German design to get fenders, which protected the hull and turret from mud. The rail antenna served as a guard of sorts.

The hatches in the side of the hull were removed, as there was no special need for them, and the large rear hatch proved more convenient. the driver had a hatch-cabin combination that could flip to the left, giving him an excellent view in travel mode for a tank with a front engine. A windshield could also be installed in travel mode.

The radiator, exposed to the elements and bullets, seems poorly thought out.

The suspension of the Rheinmetall Leichttraktor differed from the one designed by Krupp. Twelve doubled road wheels were used per side. In addition, a front wheel was added to serve as a shock absorber for vertical obstacles. The road wheels were grouped into bogeys of 4 wheels each, with a leaf spring per bogey. Removable armour protected the suspension. The lower part of the screens could flip open, allowing access to the wheels without removing it.

Commander's station in a Rheinmetall Leichttraktor.

Aside from two tanks, the Rheinmetall Leichttraktor served as a chassis for another vehicle. The Rh L.Tr. Sfl. (Rheinmetall Leichttraktor Selbstfahrlafette, self propelled gun mount on the Rheinmetall Leichttraktor) was built in October of 1930. This was effectively the same Rheinmetall Leichttraktor but with a smaller turret and no periscopic observation devices. The crew was reduced to 3, getting rid of the radio operator and his radio. A large air intake was added to the front, improving cooling but also providing an excellent target for enemy bullets. This vehicle never left Germany, travelling 1277 km across Kummerdorf. The tanks had a different fate.

Modernization with no Future

Only the laziest of writers haven't mentioned cooperation between Germany and the USSR in 1929-1933. In reality, the thesis that "the German sword was forged in the USSR" is not particularly accurate. By the way, the proving grounds that German tanks were tested at was called TEKO (Technical Courses at OSOAviaHim, the Society of Cooperation with Defense, Aircraft, and Chemical Industry), not KaMa. This cooperation was mutually beneficial. The Germans had the chance to test their tanks away from prying eyes and train their tankers (not that many, as it turned out). In return, the USSR gained much more than the Germans from TEKO, but more on that later.

Rheinmetall Leichttraktor #40 with a suspension that was redesigned as a result of trials in the USSR, extra fuel tanks, and lengthened fenders.

The Rheinmetall Leichttraktors were sent to the USSR in May of 1930, almost immediatley after they were built. Their trials began in June, combined with training of personnel.. In total, tank #39 traveled 1865 km, and tank #40 traveled 1735. The tanks returned to Germany in the summer of 1932. Turing trials, it became obvious that Kniepkamp's rubber tracks had many drawbacks. One of those drawbacks was that it was very hard to swap the track. The rear drive wheels were also less than ideal, resulting in tracks slipping off. There were also complaints about the design of the suspension.

The tank had problems of other types. The commander doubled as a loader, of both the cannon and the machinegun. Thanks to its cooling system, the machinegun took up a lot of space, and its ammo box was not small. As a result, the commander had very little space to himself. The solution was simple: the commander had to drop everything and focus on his job, but increasing the crew to 5 and adding a commander's cupola was unreal.

Rheinmetall Leichttraktor with a Christie style suspension.

Soviet specialists with access to German tanks considered the Leichttraktor obsolete. This opinion was well founded, as in 1932 the USSR already had licenses for a Christie tank and the Vickers Mk.E, which evolved into the BT and T-26 respectively. Nevertheless, the German vehicles had several technical novelties which Soviet engineers copied. One was the idea of a coaxial gun. If in the MS-1 and BT-2 the cannon and machinegun were installed separately, the two-man turret of the BT-5 and T-26 had them paired together.

Soviet specialists also liked the periscopic sights, which were used on Soviet tanks starting in 1933. The electrical trigger for cannons and machineguns was also borrowed from the Germans. German radios and welded hulls also appealed to the Soviets. In other words, the tank had a significant impact on Soviet tank design. The idea that the German sword was forged at Kazan can only cause a smile.

Rheinmetall Leichttraktor Selbstfahrlafette turned into a test lab with a new suspension.

Upon their return to Germany, the Rh.L.Tr. tanks were modernized. To start, fully metallic tracks were used instead of rubber ones. The road wheels were also replaced. An additional air intake was added to the rear of the tank. The rail antenna and fenders were lengthened and additional fuel tanks were added on the sides of the hull.

This was only the beginning. In 1933, one of the tanks received a suspension that was a variation on the Christie coil spring design. The tank had 4 large road wheels per side and 3 return rollers. The drive sprocket and idler were also replaced. These designs were also used on the Z.W. medium tank.

The Rheinmetall Leichttraktor Selbstfahrlafette also saw some changes. Trials showed that it was a worse tank rather than a proper SPG. The tank was converted into a mobile test lab for a new suspension. It resembled a Christie design, but two wheeled bogeys were used instead of large single wheels. Tracks, drive sprockets, and idlers were also replaced. Trials showed that this system is inferior to one with large wheels.

The end of the Leichttraktor's career. Tank #40 without a turret is being used as a training tank, 1936.

Aside from test labs, the Leichttraktors were used for training in Germany. One tank had its turret and turret platform removed in 1935. It was used like this for several years. The Rheinmetall Leichttraktors finished their life as monuments in front of tank unit headquarters. By then it was obvious that the layout was hopelessly obsolete.

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