Many engineering firms or manufacturers have tried and still try their hand at producing military equipment, either for lucrative contracts or as part of the mobilization of industry during war. The most widely produced AFV (Armored Fighting Vehicle) in the world, the M113, was, after all, produced by the innocuous sounding ‘Food Machinery and Chemical Corporation’ (FMC). There is a lot of sense for a car or truck maker to turn many of the same engineering skills for the production of vehicles to tanks and the French carmaker Delahaye was no different.
Sabathe and Varlet
With the First World War (1914-1919) devastating the north of France, it is no surprise that, in 1917, the Delahaye firm attempted to create their own designs to contribute to the war effort. Their chief designers, Louis-Gaston Sabathe and Amedee-Pierre Varlet, submitted a patent in March 1918 titled ‘Armement des chars de guerre’. Tanks, were, even in 1918, relatively new technology and it is not surprising that a lot of ideas for the use and development of this technology came about at this time. Sabathe and Varlet’s design, however, was very different from the existing tanks and to other tank designs of the First World War.
Their design was to use Delahaye’s own patents for caterpillar tracks filed in January 1918. These featured a relatively conventional set up of a track unit with a large diameter drive sprocket at the front and an equally sized wheel at the back which also acted as the track tensioner. Between these two large diameter wheels were three small wheels which were the load bearing portion of the system running on a thick set of metal track links. All these pieces were held together sandwiched between two triangular plates. The less conventional part of this track system was that above the level of the two large wheels was a large central pivoting mounting for the entire unit allowing it to both pivot as a single unit and around which was a chain which drove the front sprocket. This design had itself been a development of a design filed the previous January by Delahaye which had the pivot/drive for the track unit to be at the same level as the two wheels and actually connect directly to that triangular support plate. By separating the drive from this plate, the designers had neatly created a system of suspension for the track unit.
French Patents FR503169 (left) of January 1917 and FR504012 (right) of January 1918
The outline of this modified patented track unit was then featured in a second application by the firm and was specifically described in the application as being suitable for use in an assault tank. The drawing in the patent makes clear why the design was suitable for military purposes, as the vehicle body accommodated a high degree of movement making it suitable for movement over very rough terrain. On top of the flexibility of the movement which allowed the vehicle to effectively move in two halves, the track units were also shown rotating around that central pivot/drive, ensuring that the tracks would stay in contact with the ground too.
French Patent FR504013 of January 1918
With these ideas and designs at their disposal, Varlet and Sabathe continued to work on this idea, which, to function as a tank, would clearly have to have some offensive capability too. They would also expand on their track ideas to increase the off-road capabilities of their tank.
Part of this next step though meant ‘looking backward’. In July 1917, Sabathe of Delahaye had filed a patent without Varlet relating to moving assault artillery across the battlefield. This design was an unusual platform vehicle with no turret and with the field gun or artillery piece attached on a pintle mount in the middle, all surrounded and protected by and large box-shaped body with an angular front and rear. On each side were three large-diameter octagonal wheels with each face fitted with five ‘goat’s feet’ for a total 40 feet per wheel, 120 per side. As this vehicle approached an obstacle, the large platform carried above was lowered by means of a rotating boom fixed to the front axle and placed in front of the vehicle. The platform was then dropped, the obstacle crossed, and the artillery could continue its advance. This is one of the first designs for a bridge carrying military vehicle, but, although this design never progressed, the use of a non-circular wheel had shown potential to Sabathe as it could increase the ground area the wheel was in contact with improving off-road performance. Combining that idea from 1917 with the 1918 patents and a combination of polygonal wheel, and a track layer was created. This was the unorthodox triangular caterpillar wheel.
French Patent FR503609 of July 1917 showing the Sabathe designed armored trench crossing artillery vehicle
Artist’s impression of the Delhaye bridging AFV of 1917. Source: Author
French Patent FR504609 of March 1918 showing the triangular caterpillar drive wheel.
The Triangular Caterpillar
Sabathe’s ideas for polygonal wheels were combined with the work by him and Varlet for the creation of a triangular caterpillar drive unit. Although it appears to be very complicated, the system is relatively straightforward. The drive, as with the original January 1918 patents, was centrally driven via a chain from the same shaft that provided support for the unit and the axis around which it could pivot. Drive was not by chain this time, but by a toothed gear instead, and still went to a large diameter toothed sprocket wheel providing drive for the same style of heavy bodied metal track links with a flat grouser. This sprocket was fixed between a sandwich of two large triangular plates which had larger (toothless) undriven wheels at the other two corners, both of which were fitted with a track tensioning screw. All three sides of the unit were fitted with the same style of a trio of small wheels which would bear the majority of the vehicle’s load when on the ground, although, of the 9 wheels around the unit, not more than ⅓ of the track could be in contact with the ground when on flat hard ground. Sabathe and Varlet concluded their application claiming this triangular caterpillar could be used on war machines to help cross uneven and broken ground as well as trenches. Their next step was therefore logical. Combining this triangular all-terrain wheel with the flexibly coupled body from July 1917 to form a tank, offensive weapons would have to be included too.
Delahaye’s unique Tank design with triangular track system. Illustration produced by Yuvnashva Sharma, funded by our Patreon Campaign
The Tank’s Design
The design itself was a logical destination for Sabathe and Varlet who filed their tank design incorporating their ideas for tracks and vehicle in March 1918 under the title ‘Armement des chars de guerre’. This design is similar to the articulated vehicle from before, featuring a two-part body. Each section was the same basic size and shape with a roughly square body with the leading and reverse edges angled in towards the center. The rear section also sported a long cranked pair of arms extending forwards over the lead section. A large cylindrical pin then held a second set of cranked arms which curved back and down behind this first section and had a further pin fitting. The front section could, therefore, rotate sideways about this second pin as well as horizontally about the first pin. On top of the first section was a set of grooves into which another pin coming down from this second set of arms which held the first body-section in place as it rotated sideways.
These two sections could also be connected together to more tanks like this via flexible connections at the front and back of the vehicle, creating a long tank train which would be useful crossing soft or broken ground, as any vehicle becoming bogged down could be pushed or pulled by a connected vehicle either behind or in front of it respectively.
On top of this cranked arm structure was another unusual feature; an oscillating turret. This circular turret was made from a short narrow cylinder forming the body and a wider cylinder above it creating the turret itself from which projected the main gun and the whole turret was topped off with a domed roof. This body was attached to the low collar-ring attached to the cranked arms by a large pin which formed the pivot point. The pivot point allowed the entire turret to move in the vertical plane providing elevation to at least 45 degrees and up to 60 degrees although depression was restricted to -2 degrees in the field of fire by the front section of the body when firing forwards and by fouling on the cranked arm supports. The collar permitted rotation in a full 360 degrees meaning that this design could provide excellent coverage for all-road fire with the gun including the thought that this high elevation would enable it to engage flying targets. With the gun fixed in place in the turret, this meant that complex gun mountings could be completely avoided as could any weakness in the turret caused by having to allow for the gun to move. The size and type of gun for this turret was not specified in the patent except to say that it would be of an appropriate caliber to engage enemy targets including tanks, which in 1918, would have been the German A7V or captured Allied tanks. Other weapons were contained within the two body sections and included variously dispositions of 3 machine-guns, grenade launchers and small cannons. Each body section would, therefore, require at least 3 to 4 men to crew it. With at least 2 more in the turret, the vehicle would have to have a crew of at least 8 or more men.
French Patent FR504610 of March 1918.
The suspension for the design is drawn not with the unusual triangular wheels, but with the more conventional shape outline in the January 1918 patents with the pivot point lying between the two big wheels. Each section of the hull was provided with its own engine of an unspecified type which would power the two track units. Should one engine fail or become damaged, the vehicle would still be able to move and function, albeit at a limited capacity. Importantly, this design would also be able to use the patented triangular wheels, but as the pivot point was in the center of the triangle this would raise the vehicle of the ground substantially more than the system drawn in the patent.
Artist’s impression of the Delahaye 1918 Patent tank using the patented triangular caterpillar wheels. Image: Author
A photo exists of almost precisely this arrangement of triangular caterpillars on a system nearly identical to this one consisting of a two-segment body with the same cranked arm holding the pivot for one section. Between the two sections, suspended between the arms, is a turret, but strangely, this turret does not appear to have any rotation mechanism shown. It is only a model, which might explain that, but if it is missing this rotating collar, then not only does the turret appear fixed facing to the rear (assuming the front is the same as the 1918 Patent drawing), but that it is also seriously hampered in its fighting ability as it would be reliant upon the body to turn in order to aim the gun.
Model of an unknown variant of the Delahaye Tank featuring the distinctive patented triangular caterpillar drive tracks/wheels and unusual stabilization for the turret. Source: Model Archives
With the triangular wheels rotating out of sync with each other, the vehicle would end up lurching violently from left to right as it crossed any battlefield and it is perhaps for this reason why in the 1918 patent the turret is better positioned and the track units are the smaller more conventional style. Although some online sources state that this model was some continuation of the Delahaye project in the 1930s, this cannot be verified at this time due to a lack of information. It could well be a 1918 vision of what that patent design tank would look like with the triangular wheels (patented the same day) or it could be a later design.
Either way, the design was far too complex and was never adopted. By the 1930s, it would have been irrelevant anyway, as France already had the well armored and advanced Char B1 tank instead, with a much more conventional layout.
French Patent FR503169(A) filed 20th January 1917, granted 10th March 1920
French Patent FR503609(A) filed 27th July 1917, granted 21st March 1920
French Patent FR503904(A) filed 24th November 1917, granted 27th March 1920
French Patent FR504012(A) filed 5th January 1918, granted 31st March 1920
French Patent FR504013(A) filed 5th January 1918, granted 31st March 1920
French Patent FR504609(A) filed 29th March 1918, granted 19th April 1920
French Patent FR504610(A) filed 29th March 1918, granted 19th April 1920
Chars de France, (1997) Jean-Gabriel Jeudy, ETAI