Back to the 6 ton class
Improving armour technologies were the impulse that drove French tank development forward. As a rule, armoured plates at the time were connected by rivets. Rivets were suitable for bulletproof armour, but made hull design complicated. The Germans were the first to use partially welded hulls in the 1920s, but nobody knew about that yet. Another alternative was casting. Even the first Renault FT had cast hull elements and turrets, but this technology did not become popular for a number of reasons. The French returned to casting in the early 1930s, and even then, only to produce turrets.
Meanwhile, the use of cast parts significantly simplified hull production. The parts also turned out to be much more robust than riveted equivalents. Hotchkiss engineers from Saint-Denis (then a city north of Paris, today one of its suburbs) decided to risk using casting widely in tank manufacturing. The arms giant presented its first fighting machine in 1909, but that was an armoured car, and the company had no experience with tanks. Nevertheless, the concept proposed by Hotchkiss piqued the interest of the French army. At 30 mm or thicker, cast armour was easier to produce than riveted. In addition, the Hotchkiss company was offering a light tank, one that the French infantry was sorely in need of.
Renault ZM light tank model. Note the turret: it was only like this on the model.
The French army was not bold enough to give such an important project to a company that did not work with tanks before. On August 2nd, 1933, requirements were formed for a tank that would replace the hopelessly obsolete Renault FT. The requirements repeated a lot of what was wanted of the Renault D1. According to them, the tank needed 30 mm thick armour, and either two machineguns or a 37 mm cannon. The difference was that the mass had to remain at the level of the Renault FT (6 tons). The crew also had to remain the same (2 men). The average speed was also similar, 8-10 kph. In other words, the military ordered the same Renault FT, but with protection from heavy machineguns.
Renault ZM prototype on trials, late 1934.
There was a very good reason for these requirements. According to the world view of the infantry command, anti-tank tactics haven't changed since WWI. The success of the Renault FT in 1918 created the illusion that massed use of light infantry tanks would be the main way of using armour. By this logic, the more tanks could be made, the better, and small two-man tanks that combined a low price with thick armour were a real life-saver, considering the army's reduced budget. The fact that tanks in the rest of the world became faster and were turning from infantry support into a fully fledged mobile fighting force was ignored by the French military.
14 companies bid on the tender that was announced on August 2nd, 1933. Renault was one of the first. At the time, the French tank building giant was working on a whole series of projects. Among them was the Renault VM reconnaissance tankette for cavalry, later adopted under the index AMR 33. At the same time, Renault was working on another cavalry tank, the Renault VO (the second tank with this index). The concept of a small tank with a forward transmission that was tested in these tanks became the foundation for the new infantry light tank. It's worth mentioning that the French took this idea from the British. The Renault VM was a further development of the Renault UE, which was in turn a development of the British Carden-Loyd tankette.
Even though the tank weighed 7.5 tons instead of 6, it confidently drove off-road.
The new light infantry tank, indexed Renault ZM, began to take shape by early 1934. Renault engineers decided to not reinvent the wheel and present a reworked Renault VM. The tank received a hull mostly made by casting. Its shape was reminiscent of the cavalry tankette. The drive sprockets and transmission were in the front, the fighting compartment was moved to the rear. The driver was placed in a cabin that was shifted to the left.
This layout made the tank very compact. It ended up only a little longer than the Renault FT. Despite the shifted fighting compartment, the engine was not in it like on the Renault VM. The gearbox and driveshaft were on the right side of the hull. This solution avoided a common problem with such layouts: increase in height. The suspension was also not made from scratch, but taken from the Renault VO.
Renault ZM with an APX R turret. Spring 1935.
The prototype was armed with two machineguns. The turret, initially designed for a cannon, was a dome-shaped design, with the armament shifted to the right. Renault engineers calculated that there was very little room inside. The turret was redesigned, and the result was similar to the Renault VM turret, but made with casting. The turret had hatches on top and in the rear. The tank was ready by December of 1934, beating all of its competitors to trials, but the conditions of the competition already changed.
On May 22nd, 1934, the infantry command changed their requirements for the infantry support tank. The required thickness of the armour was now 40 mm, since the tank was required to resist a shot from the 25 mm gun. The machinegun variant of the tank was cancelled. The requirement for maximum speed increased to 15-20 kph. By that point, 7 companies out of the initial 14 remained in the race. In reality, contracts for production of a prototype were signed with only four: Delaunay Belleville, Compagnie générale de Construction de locomotives (Batignolles-Châtillon), Forges et Chantiers de la Méditerranée (FCM) and Renault.
Blueprints of the hull with 40 mm of armour. The tank is still indexed "Renault ZM".
Since Renault as already in the process of building a prototype, it ended up being built to original specifications. A new tank was not built. The converted prototype that was presented to the commission on December 20th, 1934, still had 30 mm of armour. Only the turret was thickened to 40 mm, increasing the tank's weight to 7.5 tons. More changes were made after the demonstration of the tank to the commission. For example, fenders were added, and the muffler was moved to the left side from the rear.
The most important change was the new turret that was installed in early 1935. Its creators were engineers from the tank department of the Ateliers de Puteaux (APX). This arms giant also participated in the tender for the 6 ton tank, but it did not receive funding to produce a prototype. This did not prevent the APX from making its own prototype. Before that, on April 18th, 1934, APX designers presented the turret known as APX R (Rueil). This turret was also used on the experimental Renault ZM. It turned out superior to Renault's own design and, most importantly, carried the armament required by the tender: a 37 mm SA 18 cannon and a MAC Mle. 1931 machinegun.
Reference Renault R 35, registration number 50004.
The tank's armament is worth a separate mention. The SA 18 gun, used in the Renault FT, was already unsatisfactory to the French military in 1926. The use of this gun in the new tank was purely economical.
For one, a financially difficult position forced the French infantry to save on everything, even on metal for new tanks. This was one of the reasons why the Renault FT replacement remained in the same weigh class. Second, there were already many SA 18 guns made for the ageing Renault FTs. Re-armament to MAC Mle. 1931 machineguns affected all tanks, both the cannon and machinegun ones. The result was an excess of available tank guns. Renault FT tanks that were written off served as another source of guns.
Renault R 35 from the front.
The mass of the tank grew again, which affected its mobility. Another problem was the short hull, which made crossing trenches a problem. The solution was simple: the tank received a tail, similar to the one used on the Renault FT.
Despite all of its problems, the modified Renault ZM was the winner of the competition. Hotchkiss, the initiator of this whole business, ducked out, and the other competitors were either no better than the Renault design or needed serious improvements. The infantry command had no other choice but to accept the Renault ZM into service on April 29th, 1935, under the name Char léger Modèle 1935 R (light tank mod. 1935 Renault).
The first order was for 300 R 35 tanks. The tanks received registration numbers starting with 50001. Another order followed this one. The infantry finally had a replacement for its ancient Renault FT.
The Char léger Modèle 1935 R quickly became the workhorse of the French tank forces.
Meanwhile, the tank's issues were not limited to its armament. By the time production began, the tank's mass grew from 6 tons to 11. The 85 hp Renault 447 engine gave the Renault ZM decent mobility, but after all of the additions to the tank, its effective power was only 7.7 hp/ton.
Renault R 35 at exercises in Normandy, 1937.
The suspension, initially, designed for a cavalry tankette and mostly suitable for flat terrain, was also full of problems. It worked poorly off road: five road wheels was not enough, and the suspension was not suitable for crossing uneven ground. Despite all these issues, 1540 Renault R 35 tanks were built. The total order was even larger (1800 tanks + 500 more as soon as the war broke out), but reality interfered with these plans.
Sad result of economy
A certain sobering revelation took place in 1937. The French military could not ignore the worrying news from the front lines of the Spanish Civil War, where 3.7 cm Pak anti-tank guns were used en masse. In June of 1937, the R 35 tank with registration number 50004 was fired upon first by a French 25 mm gun and then a German 3.7 cm Pak. The results were unpleasant.
R 35 number 50004 after trials. The results were a shock to the French military.
It turned out that the thickness of the armour does not necessarily mean protection. The issue with cast armour is that its effective protection is about 10-15% less than that of rolled steel. Out of 18 shots fired from the 3.7 cm Pak, 14 penetrated. Neither the hull nor the turret of the tank were a serious issue for the German gun.
Another unpleasant surprise was that out of 22 shots from the 25 mm gun, 13 also penetrated the Renault R 35. It's not surprising that the French infantry began looking at the FCM 36 with renewed enthusiasm after such shocking results. Even though the tank cost twice as much as a Renault R 35, it was assembled from sloped rolled armour plates that were connected by welding. The suspension of the FCM tank was also much more adapted to off-road driving.
Tank number 50332, experimentally equipped with the Tourelle FCM. Due to an identical turret ring diameter, this replacement was easy.
Unfortunately, it was too late to make serious changes. No matter how good the FCM 36 was, the production abilities of Forges et Chantiers de la Méditerranée were limited. Even Renault could not cope with the military's demands, resulting in an order for 100 Hotchkiss H 35 tanks.
A partial solution to this problem was the replacement of the APX R turret with the welded Tourelle FCM, used on the FCM 36. There was a good reason for this, as rolled armour is more robust than cast, but there was another issue.
One of the few Renault R 35s to receive the 37 mm SA 38 cannon.
In 1938, the French military suddenly realized that the SA 18 gun will soon be incapable of penetrating even a light tank, given the tendency of armour to grow. The result of this overdue realization was the SA 38 gun, capable of penetrating 29 mm of armour at 100 meters. Of course, this was not enough for 1938 (the Germans were making tanks with 30 mm of front armour), but already better than the SA 18, which could not even penetrate 20 mm. However, trials showed that the Tourelle FCM's welding seams began to crack after intensive firing.
As a result, the new gun had to be installed into the cast APX R turret. Even that replacement took time, since Hotchkiss H 35 and their replacement, the H 39, also needed these guns. Because of this, the Renault R 35 only began receiving SA 38 guns towards the end of their production. One of the first tanks to receive this gun was number 51295. This allows us to conclude that there were fewer than 250 long barreled R 35s. That number is likely much smaller. A review of photographs shows that about half of all tanks built after 51295 are armed with the old SA 18.
Renault R 35 destroyed in May-June of 1940. The incorrect ideas regarding tank tactics and attempts at economy proved fatal for the French army.
The consequences of the army's archaic thinking were obvious in May and June of 1940. It's worth mentioning that the Poles were the first to try this tank in combat. The Polish army bought 50 tanks of this type, but poor crew training and other causes negated the advantages of these tanks in September of 1939. Some of the tanks were captured by the Germans and the Red Army intact. Polish 7TP tanks proved more effective, since they were much more maneuverable and could penetrate any German tank easily.
As for battles in France, their results were predictable. The Renault R 35 was the most widely used French tank of WWII (not counting the Renault FT), but it was completely unsuitable for it. There were no WWI style charges of hundreds of tanks. The Renault R 35 had to fight a highly mobile opponent. French tank battalions that used Renault R 35 tanks were effectively observers that could not affect the course of the war. The French fought fiercely, but what can you do when your gun cannot penetrate most German tanks, but their 37 mm gun can penetrate you at 300 meters?
In addition, the French tank commander was also a gunner and a loader, sometimes a radio operator. Even the old and unsuccessful Renault D1 was more effective in comparison. The French paid dearly for their mistaken ideas of what the future of warfare would be like.