Krupp Grosstraktor during trials, source: Flickr.com with permission of the publishing user, edited

A Dangerous Tractor

Among the many categories of weapons prohibited to Germany by the Treaty of Versailles, the development and manufacture of tanks was explicitly banned. The more forward-thinking elements of the German military leadership were well aware of just how serious a handicap this embargo could prove for the future of their armed forces. There was the risk of losing the invaluable experience gained by the first tank crews in the closing stages of the Great War, and of cutting the industrial base off from emerging development trends and modern technologies. It is therefore hardly surprising that covert violations of the Versailles provisions began relatively early. As far back as the mid-1920s, a secret programme for the development of light and medium tanks was underway, camouflaged under the innocent designation of "Traktor." The medium tank that emerged from this programme went down in history under the name Grosstraktor – literally "large tractor."

The official requirement for the development of such a vehicle was issued to Daimler-Benz, Krupp, and Rheinmetall-Borsig in 1925. At that stage it was still known by the code designation Armeewagen 20 – literally "Army vehicle 20" – which was only later changed to the familiar Grosstraktor. Each firm was to design, build, and deliver two prototype vehicles made from ordinary unarmoured steel for testing. Delivery of the prototypes was expected around the turn of 1929–1930.

Army Requirements

The Army specification called for a vehicle in the 15-tonne weight class with a hull length of no more than 6 metres. The required weight is sometimes quoted as 20 tonnes, which might explain the origin of the number 20 in the code designation Armeewagen 20. The tank was to have armour between 6 and 14 mm thick and a maximum speed of around 40 km/h. Its main armament was to be a 75 mm gun with a barrel length of 24 calibres. Secondary armament was to consist of 2 to 4 machine guns. Some authors also mention that the Army required the new tanks to be capable of swimming.

Rheinmetall-Borsig Grosstraktor preserved as a monument, source: Flickr.com with permission of the publishing user, edited

Each firm was to design and manufacture the components for its own vehicle, with Rheinmetall carrying out the final assembly of all prototypes. In addition, Daimler and Rheinmetall were to reach an agreement regarding the turrets: under this arrangement Rheinmetall was to develop and build the turrets not only for its own prototype but also for the Daimler-Benz vehicle. Some historians argue that the Army specification included a requirement for broad interchangeability of major components between the manufacturers' designs – a theory that the close similarity of the three finished vehicles would certainly support.

All three designs showed the clear influence of First World War construction standards and of British and French heavy tanks. The track assembly was very tall, with the upper run of the track reaching as high as the hull roof. At the front of the hull was the driving position, followed by the crew compartment with the main fighting turret above it. Behind the crew compartment was the engine section, and at the very rear a secondary machine-gun turret.

Daimler-Benz Prototypes

The Daimler-Benz prototypes were completed on schedule – the first in 1929 and the second in 1930 – yet were last among all three competitors to be finished. To distinguish between the vehicles of the different manufacturers, each was assigned a Roman numeral. Despite being last to be completed, the Daimler-Benz design was designated number one and was therefore known as Grosstraktor I. The Daimler prototypes weighed 15 tonnes, making them the lightest of all three. Power was provided by the Mercedes DIV (M182206) engine, which produced a maximum output of 260 hp – though some sources give 300 hp.

Daimler-Benz Grosstraktor preserved as a monument, source: Flickr.com with permission of the publishing user, edited

The running gear of Grosstraktor I consisted of sixteen small road wheels on each side. The first two wheels were positioned above ground level and served to support the track when mounting an obstacle. The road wheels were paired into eight two-wheel bogies. The rearmost six bogies were then grouped in pairs and suspended from a shared mount using a single large horizontal leaf spring. Almost the entire track assembly was covered by external side armour featuring semicircular service openings – it is in fact these distinctive openings that make the Daimler-Benz vehicle easy to identify in photographs.

The front of the hull was formed by sharply angled upper and lower plates meeting at a rounded nose. A machine-gun embrasure was located in the right side of this nose. Towing hooks were attached to the lower front plate.

A large headlight housed in a closable metal casing was set into the centre of the upper front plate. This plate transitioned into the roof of the crew compartment. In the forward part of the compartment sat the driver on the left and the hull machine gunner on the right, positioned side by side. Each was provided with his own cupola overhead, circular in plan and fitted with vision ports around its circumference. The top of each cupola was almost certainly fitted with an access hatch.

Krupp Grosstraktor preserved as a monument, source: Flickr.com with permission of the publishing user, edited

Behind the driver's and machine gunner's positions came the crew compartment for the remaining three soldiers and the main fighting turret. The turret walls tapered conically, which increased their resistance to enemy fire. A 75 mm gun and a coaxial machine gun were mounted in a movable mantlet in the front wall. The side walls of the turret featured small closable circular openings, most likely pistol ports for the crew's personal weapons. The commander, gunner, and loader were stationed in the turret, entering and exiting via a hatch in the turret's rear wall – and possibly also through one in the roof.

Behind the main crew compartment came the engine section, followed by a second, smaller turret. This rear turret sat lower than the roof of the engine section and therefore could not rotate fully – it was intended to cover only the area to the rear of the tank. A heavy machine gun, operated by the sixth and final crew member, was installed in it. The exact type of machine gun could not be determined, but it was evidently a water-cooled design, whose barrel jacket consequently resembled a gun barrel more than a machine-gun barrel.

According to some sources, one of the Daimler-Benz prototypes was later fitted with a longer-barrelled gun. This conclusion seems to have been drawn from a photograph of a Daimler Grosstraktor serving as a monument outside the barracks of the 5th Panzer Regiment in Wünsdorf. However, the question arises as to whether this is a genuine gun at all. Why would anyone go to the trouble of fitting a new gun type into a tank destined to stand on a plinth as a memorial? It seems far more logical to remove the gun entirely, use it elsewhere, and replace it with a dummy barrel for display purposes. One could argue that a new gun might have been installed during an earlier phase of prototype modification, long before the decision was made to convert the vehicle into a monument. Yet this seems unlikely, since the Daimler prototype was withdrawn from trials early due to persistent mechanical problems, and its armament was certainly not where improvements were needed. Incidentally, photographs also exist in which the gun has been completely removed from the Daimler Grosstraktor's turret, leaving only the tube that formed the inner section of the barrel projecting from the mantlet.

Rear view of the Daimler-Benz Grosstraktor, source: forum.worldoftanks.eu, edited

Rheinmetall-Borsig Prototypes

Rheinmetall-Borsig delivered its two prototypes even before Daimler, specifically in 1928 and 1929, yet the Rheinmetall Grosstraktor was designated number II. As already noted, the overall design of the vehicle was very similar to its competitors. The running gear again consisted of a large number of small road wheels, a rear drive sprocket, a front idler, and three return rollers. This tank had either eighteen or nineteen road wheels in total. The first two were positioned above ground level, below the idler, to support the track when mounting obstacles.

The entire side of the hull was again covered by armour plate. The powerplant in this case was the BMW Va aero engine producing 250 hp. Worth noting is the railing visible in some photographs surrounding the uppermost part of the hull – this was most likely an actual railing rather than a frame aerial for the radio, as it might otherwise appear. The hull layout of the Rheinmetall vehicle corresponded to that of the Daimler prototype described above. The turrets were entirely identical across both designs, since Rheinmetall-Borsig was responsible for producing the turrets for both Grosstraktor I and Grosstraktor II. Weighing 19.3 tonnes, Grosstraktor II was the heaviest of all three competing designs.

At least one example of Grosstraktor II was also used as a monument outside barracks – again apparently those of the 5th Panzer Regiment. Photographs of this monument show an unusual armament combination in the main fighting turret, with what appears to be both a 37 mm and a 75 mm gun installed side by side. Such a combination – incidentally also used later on the Neubaufahrzeug – would certainly have made tactical sense, pairing anti-tank capability (37 mm) with infantry support (75 mm). Based on careful study of the photographs, however, I would venture to suggest that here too the weapons are dummies fitted into the turret of the monument vehicle in place of the originals. That said, one must ask: where did the idea for this particular dummy arrangement come from? It is theoretically possible that the two guns were experimentally fitted to Grosstraktor II as part of its development modifications.

Krupp Grosstraktor preserved as a monument, source: Flickr.com with permission of the publishing user, edited

Krupp Prototypes

As is now clear, the Krupp Grosstraktor received the designation III. Krupp delivered its vehicles in 1928 and 1929. The running gear consisted of 12 small road wheels paired into bogies on each side, plus a further 2 or even 4 independent wheels. The rear wheel was the drive sprocket, the front the idler, and the upper run of the track was carried by the customary trio of return rollers. Here too the hull sides were covered by a large armour plate, though unlike the other two designs, Krupp left the drive sprocket entirely uncovered. The powerplant was, as in Grosstraktor II, the BMW Va aero engine. The weight of the Krupp prototypes was between 16 and 16.4 tonnes.

The armour thickness was identical across all three manufacturers' prototypes, ranging from 6 mm on the floor plates to 13 mm on the front hull. Ammunition stowage was also reportedly the same for all: 104 rounds for the 75 mm gun and 6,000 rounds for the machine guns. As for maximum speed, all Grosstraktors met or exceeded the Army's requirement of 40 km/h. The question of swimming capability remains highly contentious. According to the literature, propulsion during swimming was to be provided by propellers at the rear of the tank. Photographs of the rear of Grosstraktor vehicles (for example HERE, HERE, or HERE) reveal no sign of propellers whatsoever. And yet some authors go so far as to state that swimming trials did take place – and that one of the Rheinmetall prototypes actually sank during such trials in October 1929!

Testing in the USSR

In 1930 all the completed development vehicles were sent to the Soviet Union for trials at the Kama proving ground. The Kama training and testing centre had been established as part of Soviet-German cooperation in armoured vehicle development, and it operated until Hitler came to power in 1933 – and it was until that year that the Grosstraktors (or at least some of them) remained there. The trials exposed a long list of shortcomings. The Daimler-Benz prototypes – Grosstraktor I – reportedly fared worst of all. Between them they covered only a few dozen kilometres before persistent breakdowns and failures forced them to be taken out of service. They spent most of the remaining time in the repair workshops and were apparently even withdrawn from further testing and returned to Germany ahead of the other vehicles. The Rheinmetall-Borsig Grosstraktor II vehicles performed best, though even they required numerous repairs, modifications, and alterations during the course of the trials – possibly including the fitting of the twin-gun arrangement mentioned above.

Rheinmetall-Borsig Grosstraktor serving as a target for Panzerschreck training, source: Bundesarchiv_Bild_146-1979-107-13, Wikimedia, Creative Commons, edited

Since the prototypes had been built from unarmoured steel, ballistic testing was apparently not carried out, meaning their resistance to fire could not be objectively assessed. From the armour thicknesses specified, however, it is clear that the tanks would have withstood fire from small-arms anti-tank rifles but not from anti-tank guns. Overall, the Grosstraktor programme was considered a disappointment. Nevertheless, it provided German designers and the Army with valuable experience. Among other lessons, it confirmed once again that the concept of multi-turreted tanks was outdated. In the case of the Grosstraktor specifically, the soldier in the rear machine-gun turret was completely cut off from the rest of the crew and unable to coordinate his actions with them effectively.

When Soviet-German cooperation ended in 1933, the four Grosstraktors still in the USSR at that time (the Daimlers having apparently been returned earlier) were brought back to Germany. As already noted, the unsuccessful Daimler-Benz prototypes were put on display as monuments – one at the barracks of the 1st Panzer Regiment in Erfurt and one at the 5th Panzer Regiment in Wünsdorf. The remaining prototypes were perhaps used for further training purposes and reportedly took part in military manoeuvres as part of the 1st Panzer Division in 1935. At least one Krupp and one Rheinmetall vehicle were also eventually turned into monuments, apparently at the gunnery school in Putlos. During the war, at least some of the Grosstraktors were used as live-fire targets for training with hand-held anti-tank weapons, and were presumably scrapped thereafter.

ARTICLE
CONTENTS:

A DANGEROUS TRACTOR

ARMY REQUIREMENTS

DAIMLER-BENZ

RHEINMETALL-BORSIG

KRUPP

TESTING IN THE USSR