Saturday 3 June 2017

Renault R 40: Incorrigible

The Char leger Modele 1935 R that was accepted into service by the French army on April 25th, 1935, was a compromise. Created as a replacement for the Renault FT, it did not surpass its predecessor by much in speed, and the armament remained the same. Of course, the new tank had more powerful armour, but experience showed that you could not rely on it. The French infantry began looking at the FCM 36, an expensive tank, but one that was more suitable for the infantry tank role. The Renault R 35 could only be rescued with a modernization of its weakest link: the suspension. A new tank with a superior suspension and a longer gun received the index R 40. It finally satisfied the requirements of the customer, but it was too late.

In search of a superior suspension

The Renault R 35 was a victim of the French army's desire for more armour with the same dimensions. As a result, the tank quickly left the 6 ton weight class and surpassed the 10 ton mark towards the end of its development. Its mobility could not remain the same. In this case, the problem was not with speed. The French infantry did not prioritize a high speed. The R 35 was tasked with supporting infantry attacks, and infantry, no matter how much it wants to, can't run across the battlefield as fast as a horse.

The main weakness of the Renault R 35 was the suspension, and this weakness was not revealed right away. Renault engineers used their previous experience with the Renault VO cavalry tank when designing the Renault ZM. The suspension was compact and worked well on a level road. It also showed itself well on the experimental Renault ZM. The problem was that it was designed for a different weight class and for a different purpose. It didn't break, but when the Renault R 35 was delivered to the military, it turned out that its suspension was unsuitable for off-road driving.

The problems that the French were facing were, in a way, similar to what the Japanese encountered with the Ha-Go in Manchuria. The Japanese solved that problem by installing special mounts with an additional road wheel on each side. The French, however, were unsatisfied with a half-measure like that, since the target theater of war was right under their noses. The French infantry commanders first began looking at the FCM 36 because of its superior off-road performance (not to mention its welded hull, sloped armour, and diesel engine).

Dissatisfaction with the R 35's suspension grew gradually. By 1938, it entered the practical phase. Infantry command decided that the Renault R 35 will be produced with the current suspension up to tank #1500. The 1501st tank must have a modernized suspension, and all existing Renault R 35s will be modernized and have their suspension replaced.

By that point, the Renault assembly plant was nationalized and reformed into the Ateliers de construction d'Issy-les-Moulineaux, or AMX for short. In early 1938, AMX engineers began working on a new tank that could replace the Renault R 35. However, the AMX 38 was still up in the air, while the unsatisfactory Renault R 35 suspension was an immediate issue. Even after this restructuring, Renault remained a dominant force in French tank building, and its engineers never stopped working on new tanks and components. However, Renault no longer held a monopoly on the modernization of its own tank.

Renault R 35 with a suspension designed by Lorraine.

One of the companies that tried its luck at modernizing the Renault R 35's suspension was Lorraine. This fragment of the Lorraine-Dietrich automotive company moved to military projects in the early 1930s. The company's biggest success was the contract fro Lorraine 37L tracked prime movers. This suspension from this vehicle was tried on the R 35. The modernized tank entered trials in the spring of 1938. As on the Lorraine 37L, the number of road wheels was increased to 6 per side, and the idler was lifted off the ground. The tracks were also taken from the prime mover. To reinforce the design, the bogeys were connected with a beam.

The result was far from idea. In order to install the new suspension, 118 new holes in the hull had to be drilled. The mass of the modernized tank also grew by 1.5 tons. It's not surprising that the military declined this proposal.

The first variant of the Renault modernization. No comment.

Renault began its modernization with a simple idea. The first variant replaced each road wheel with two wheels of smaller diameter. These wheels were attached to a separate bogey. The result was an unusual design with 10 road wheels per side, but at what cost! The design was much more complicated, and trials showed that this system was hopeless.

Renault's second variant with a stretched suspension.

The second attempt was not any more complicated. A decision was made at Renault that the issues of the suspension came from insufficient length. The issue was resolved by increasing the wheel base. The idler was moved far back and a sixth road wheel was added in its place. This "improvement" increased the tank's mass by 700 kg and did not solve any problems with the suspension.

Many changes were made to the tank as a result.

The third modernization was final. It looks like Renault remembered what they did with the Renault NC. as the design created in 1939 has many similarities with France's first mass produced interbellum tank. The new suspension contained 9 road wheels per side, combined into bogeys with horizontal springs. The suspension and road wheels were covered with screens.

Even though the third modernization increased the tank's mass by 2 tons, the French infantry command was interested. There was no chance of using this suspension in new production, but it could be installed on existing tanks. Plans were made for the modernization of 800 existing tanks, but it was not meant to be. AMX managed to do the job much better.

Renault's last try at modernization of the R 35's suspension. This variant was better, but AMX still won.

AMX engineers did not try to make their jobs harder. The first modernization variant was simply the installation of the AMX 38 suspension on the R 35. The number of road wheels grew to 12. This modernization was never performed in metal. The suspension used in trials was a different one, similar to Renault's third variant.

AMX's first suspension proposal.

A commission from the infantry command summarized the results of the contest and awarded victory to AMX. The modernized tank was indexed Char léger Modèle 1935 R modifié 1939. The military liked the suspension so much that it was proposed for the Hotchkiss H 38 tank, but the cavalry declined this offer. It didn't need another 700 kg of weight, and cavalry tanks mostly drove on roads, not fields.

End of the campaign

Despite the fact that the new suspension was much more suitable for off-road driving, the French military did not rush it into production. In their opinion, there was no need to change approved plans, and the first 1500 tanks should be produced with the old suspension. This seems strange, especially since old tanks would be modernized anyway after the Char léger Modèle 1935 R modifié 1939 entered production. 

The modernization process was not influenced by the start of WWII. According to the production schedule, completion of the 1500th Renault R 35 and the switch to Char léger Modèle 1935 R modifié 1939 was scheduled for February of 1940. The reality was different: the old Renault R 35 lasted a month longer than expected on the assembly line. The last tank produced had the registration number 51540, meaning that 1540 units were built.

The new suspension was anything but simple.

By the time the new tank entered production, two events took place that impacted its fate. The first was that the tank received the name Renault R 40. This is logical, considering the year that it was put into production.

The second event was much more important. French industry finally managed to produce the long barreled SA 38 37 mm gun in sufficient amounts to install it on all tanks. The Renault R 40 shrugged off one of the drawbacks of its predecessor: a gun that was worthless against tanks with 20 mm of armour or more.

Even though the new tank was assembled at an AMX factory and its suspension was designed by AMX, it was still called Renault. Its components were still being manufactured at Renault, and even the new suspension was built at a Renault factory south of Le Mans.

The start of production of the Renault R 40 was affected by a number of factors. The first was that AMX still had an order for B1 bis tanks. Furthermore, it was significantly increased. The infantry command finally realized (after almost five years) that the Char G isn't going anywhere, and hurriedly ordered fifty Renault D2. The resources of the factory at Versailles-Satory weren't infinite.

The first Renault R 40 with registration number 51541 left the assembly line in March of 1940. Considering its workload, AMX could not keep up the production volumes of the Renault R 35 (70 tanks per month). Due to the chaos during June of 1940, nobody knows the total number of Renault R 40 tanks produced. The biggest registration number encountered in photographs is 51670, meaning that at least 130 were built. François Vauvillier claims that 155 tanks were built, but the real number is likely fewer. Even if there were 155 Renault R 40 tanks built, the average monthly production was only 50 units, not a lot for a mass production tank.

Tankers from the 40th Tank Battalion (BCC, Bataillon de Chars de Combat) with their new tank, May 1940

The first unit to receive the Renault R 40 was the 40th Tank Battalion. This unit had 15 Renault R 35 and 30 Renault R 40 tanks on May 19th, 1940. Its first battles on May 31st near Corbie showed the superiority of the new tanks over old ones. The battalion lost nine R 35s, but the R 40s only received damage to observation devices. The battalion continued fighting defensively until the end of the war, and had 27 tanks left over by June 18th.

The next recipient of the new tanks was the 48th Tank Battalion, which took in 16 R 35 and 29 R 40. The battalion's debut at Abbeville, where 11 tanks were lost, also demonstrate the R 40's superiority. By June 8th, the battalion had 26 tanks left, predominately R 40s.

Another unit with Renault's tanks had them in nearly equal numbers (21 R 35 and 24 R 40) was General Maczek's 2nd Polish Battalion. These were the same men who fought in the 10th Armoured Cavalry Brigade in the fall of 1939. However, they quickly transferred their tanks to the 25th Tank Battalion, which used Hotchkiss H 39 tanks prior to that. The battalion was fighting near Somme in early June, and had 6 tanks left at the end of the campaign.

As for the Poles, they were the last to receive the R 40 (13 units on June 19th). They did not have a lot of time to fight. The personnel were quickly evacuated to Britain where they formed the 1st Polish Tank Division.

Renault R 40 from the 48th BCC.

Overall, the career of the R 40 could be described as successful. The modernized R 35 was more successful than its predecessor, and the longer gun increased its effectiveness in battle. Nevertheless, there was no huge leap in quality. Even with the modernization, the Renault R 40 was obsolete.

At war's end

As with the Renault R 35, some R 40 tanks (around 30) fell into German hands. The tanks were given the index Panzerkampfwagen 40R 736 (f). Some of the captured tanks were still in warehouses. The Panzerkampfwagen 40R 736 (f) is practically the only French light tank that the Germans did not convert into SPGs or special vehicles.

There are several reasons for this. One is that, in comparison with the R 35, the Germans captured a miserly amount of tanks. The new suspension was also more complicated than on the Renault R 35. The Germans decided to spare themselves the extra headache, and the Panzerkampfwagen 40R 736 (f) never left France.

Panzerkampfwagen 40R 736 (f) captured by the Free French.

The Panzerkampfwagen 40R 736 (f) was equivalent to the R 35 as a training tank, and this is the role that it was used in. As on the R 35, the Germans cut off the commander's cupola and installed a two-piece hatch. The captured tanks survived in this form until the summer of 1944. At least several Panzerkampfwagen 40R 736 (f) remained in the Paris garrison. In August of 1944, one tank was captured by the Parisians and went into battle against the Germans.

Alas, time was not kind to the R 40: not a single surviving tank of this type is known.

Military Police Renault R 35. The missing commander's cupola indicates that the tank formerly served the Germans.

As with the Renault R 35, the reclamation of French territory by the French army meant that the tanks returned into service. They did not see the front lines, but were often used as auxiliary vehicles. Some of these tanks were never converted by the Germans, as they were squirreled away during the occupation. The career of the R 35 did not end after the war. These tanks were even modernized. Some R 35s received the long SA 38 cannon. These tanks were included in the military police which was used in the French occupation zone in Germany.

The first variant of the Automoteur-Canon de 16 livres sur chassis R 35, conceptually similar to the German 4.7 cm Pak(t) (Sfl) auf Fgst.Pz.Kpfw.35 R 731(f) tank destroyer.

To wrap up, it's worth mentioning a far more radical modernization than the installation of a longer gun. Work began during the German occupation, even though it only reached the draft stage in the fall of 1945. Looks like AMX engineers were impressed by Alkett's work an decided to develop something similar to the 4.7 cm Pak(t) (Sfl) auf Fgst.Pz.Kpfw.35 R 731(f). 

Even the name Automoteur-Canon de 16 livres sur chassis R 35 (self propelled 16-pounder gun on the R 35 chassis) is reminiscent of its German analogue. The layout was also similar. 58 rounds of ammunition was kept in the main ammunition rack in the rear bay. The name of the gun was erroneous: AMX engineers were going to use the British 17-pounder gun. Even the Germans did not attempt installing such a large gun on such a small chassis. The mass of the resulting SPG was optimistically estimated at 12 tons. The layout was similar to the 4.7 cm Pak(t) (Sfl) auf Fgst.Pz.Kpfw.35 R 731(f), but the size of the fighting compartment was larger. The casemate was going to be cast, and it shape was very complex.

The second variant of the Automoteur-Canon de 16 livres sur chassis R 35. This time, the gun is pointing backwards.

This was not the only AMX project of its kind. In parallel, another Automoteur-Canon de 16 livres sur chassis R 35 project was in development, with a noticeably different layout. Its mass was estimated at 11 tons, which was even less believable. However, the layout also raises many questions. AMX engineers couldn't think of anything better than to turn the gun backwards. The ammunition rack moved to the engine compartment, and the ammunition capacity decreased from 70 rounds to 42. The crew consisted of two men.

This layout raised serious issues about the load on the suspension. If the weight was evenly distributed in the first variant, the second variant's rear road wheels were noticeably overloaded. Nevertheless, neither project was ever built in metal. The Renault R 35 was hopelessly obsolete, and the tanks themselves were heavily used. It was easier to let the old veterans retire and use British and (especially) American self propelled guns.

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