Char de Bataille SRB

France (1921-1925)
Experimental Infantry Tank – 1 Prototype Built

One of, if not the most famous French tanks of the Second World War was the B1 heavy tank and its improved model, the B1 bis. These large infantry tanks were some of the most heavily armed and armored tanks that existed in the world during the late 1930s. While their production only started in the second half of this decade, they had roots going back as far as 1921, with the Char de Bataille program that started a search for a medium, well-armed tank to fill in the void between the small and numerous Renault FT and the gigantic and rare FCM 2C tanks. Within the proposals offered to this program was one designed by the tank and artillery manufacturer Schneider, in collaboration with the motorized vehicle giant Renault: the Schneider-Renault B, or SRB.

Estienne and the Char de Bataille

Arguably the most important figure of the first years of French tank development was general Jean Estienne. Nicknamed the “Father of Tanks” in France, Estienne, a major proponent of the use of armored vehicles from 1915 onward, was named the director of the AS (Artillerie Spéciale – Eng. Special Artillery), the French armored force, in September of 1916. It is largely thanks to his intervention to the Grand Quartier Général, France’s general headquarters, that the FT light tank reached mass production. Estienne was also a proponent of the Schneider CA1, the first French tank to see service.

At the end of the war, Estienne continued in his role as the leading figure of French armored development. He was still at the head of the AS, which was attached to the French infantry and renamed the Subdivision des Chars de Combat (Eng: Combat tank subdivision), and he was also named Inspecteur des Chars de Combat (Eng: Combat Tank Inspector). In this position, Estienne had large amounts of power over the future development of French armored technology. With the French military having large quantities of largely effective light tanks thanks to the mass production of the Renault FT, and with the development of large tank already underway at FCM since 1916, with the FCM 1A and then FCM 2C super-heavy tanks, what the French military lacked in his view was an intermediate vehicle between the dwarves and the giants. A ‘Char de Bataille’ (Eng. battle tank) was desired, thought of as a vehicle of medium weight that would feature a fixed 75 mm gun able to engage enemy fortifications and positions and to move through the devastated terrain typical of trench warfare in an artillery-saturated battlefield. Estienne thought the type would offer the ideal compromise, mounting an armament capable of knocking out enemy fortifications and trenches, something the FT’s armament of either a machine gun or a 37 mm gun struggled with while being vastly more reasonable and easier to mass-produce than a monster the size and weight of the 69-tonne, 10-meter long 2C. If successful, the Char de Bataille would have eventually become the workhorse of France’s armored force.

The Char de Bataille program and the Estienne agreements

In 1921, Estienne gathered five of the largest French industrial companies: Schneider, Renault, FAMH/Saint-Chamond, FCM, and Delaunay-Belleville, and gave them the requirements of the Char de Bataille which he requested them to design. The vehicle was to have a weight of 13-tonnes, and feature a hull-mounted main gun: either a 75 mm howitzer with a muzzle velocity of 350 m/s or the higher velocity 47 mm mle 1902 naval gun, with 750 m/s muzzle velocity. The tank was to have a turret armed with either one or two machine guns. It was to have a power-to-weight ratio of at least 8 hp per ton and be able to run for 8 to 10 hours. The armor was to be 25 mm thick.

Most importantly, the program was not planned to result in the immediate adoption of the product that answered to the specifications the most. The plan was that, once the prototypes were produced, the most interesting features from each would be taken to then be featured in a new tank design that would not be the property of a company, but of the state. The objective of such a move was to reduce competition and encourage the manufacturers to innovate without the risk of a yet not entirely mastered concept leading to the refusal of a proposal. Once the vehicle that combined the best features of each proposal was adopted, each of the manufacturers involved would play a part in the production. This original policy was named the Estienne agreements.

Schneider-Renault Collaboration: Common features, separate designs

While FAMH and FCM went to design and build their own prototypes in complete independence from other firms, Schneider and Renault decided to collaborate to produce two different prototypes. This collaboration mostly consisted of some major elements of the prototypes being shared by both: notably the turret, designed by Schneider, and the powerplant, designed by Renault.

The design of the vehicles and their manufacturing outside of those two major elements, though, remained independent. The second prototype, the SRB, was designed and manufactured by Schneider in its facilities of Le Creusot, in Burgundy, while the SRA was produced by Renault in Billancourt, in the western suburbs of Paris (the SRA is even known to have had an internal designation code, Renault JZ). Still, the hulls of the vehicles in their design appear to be almost identical, though some significant differences exist in the suspension and armament that were fitted to those hulls.

The SRB: Bearer of advanced features

The overall shape of the SRB’s hull was remarkably similar to its SRA sibling, taking the shape of a mostly rectangular vehicle, with two front plates angled backward, the driver’s vision port being featured on the higher one. The first major difference between the two designs was the gun mounted to the right of the vehicle. While the gun mount was identical on both vehicles, the SRB, instead of a short 75 mm howitzer, mounted a 47 mm model 1902 naval gun, a weapon originally designed as an anti-torpedo boat weapon mounted on many French ships of the early 20th century.

This weapon was present as an alternative to the 75 mm in the requirements formulated by Estienne, however, all other manufacturers opted for the 75 mm option, which may have appeared as a better option in the anti-fortification role the Char de Bataille was designed for. The 47 mm, however, offered a better velocity than the 75 mm. 750 m/s is generally quoted as the muzzle velocity of the SRB’s gun, which would suggest some modifications to the weapon, as the standard version is known to have had a muzzle velocity of 690 m/s. This was in any case superior to the 350 m/s of the 75mm howitzer. The gun had a semi-automatic action, giving a maximum rate of fire of 15 rounds per minute. While it is likely this would have been lower in the constraints of an armored vehicle, the 47 mm gun retained a better rate of fire than the 75 mm. It also had some decent anti-armor capacity. With the Obus de rupture acier mle 1911 G armor-piercing shell, it could reportedly penetrate, at an incidence of 30°, 40 mm of armor at 500 m, and 30 mm at one kilometer. Whether or not mounting the 47 mm on the SRB was intended to give the vehicle anti-armor capabilities is not known. A problem that has been suggested with the 47 mm’s quite long barrel is that it could possibly hinder the SRB’s crossing capacities, as the barrel extended beyond the hull.

As on the SRA, the mounting of the gun to the right of the hull on the SRB left a great deal of space for the driver. The SRB featured two large hatches on the side of the hull. In comparison to the SRA’s hatches, the SRB’s appeared to be taller, more rectangular, and less square-shaped. The suspension of the SRB is not known in as much detail as its SRA sibling, but it is known to have made use of leaf springs. 14 small wheels can be counted on the bottom of the vehicle. The SRB had a front-drive sprocket and rear idler wheel. The suspension was at its highest point in front of the side hatch of the vehicle. Unlike the three other prototypes, which used wooden pads track with a considerable pitch, the SRB used metallic tracks inspired from the Renault FT’s, which each pad directly linked to the other. The armor of the vehicle was 30 mm at its thickest, on the vehicle’s front. This was an impressive amount for 1925. The SRB was 6 m long, 2.50 m wide and 2.38 m high, making it the longest of the four Char de Bataille prototypes. The ground clearance was 0.41 m, and the tank had a weight of 19 tonnes.

The engine, which was designed by Renault, was a six-cylinder one based on a bisected 12-cylinder aircraft engine. It produced 180 hp at 1500 rpm. This was 60 hp more than the Panhard 120 hp engine used on the FAMH and FCM. Despite being the heaviest tank in the competition, at 19 tonnes, the Schneider-Renault prototypes also had the highest power-to-weight ratio, with 9.5 hp/tonne. The SRB consumed 20 to 35 liters of fuel an hour, and its fuel tanks contained 370 liters, giving an average range of about 125 km. The tank had a maximum speed of 18 km/h on a road and could cross a 2.50 m gap. The transmission was at the rear. Arguably the most advanced feature of the SRB laid within its transmission. The vehicle had been fitted with a Naeder hydrostatic system. The purpose of this system was to allow for precise neutral steering of the hull in order to point the hull gun, which had no lateral traverse in its mount. It consisted of a system that received the movement of the engine and used it to move a fluid (a form of castor oil), sucking it in or out. This was used to operate slow and precise movements of the tracks in order to aim the hull. The hydrostatic system was used thanks to a steering wheel the driver/gunner of the vehicle could use. It allowed for very precise movement but also required the use of both castor oil and regular oil (as the engine was used & it was also necessary to heat up the castor oil at a proper temperature).

The turret featured on the SRB as well as the SRA was of Schneider design. This was a cast design, a particularly modern feature for the early 1920s, with an inclined roof, being at its highest at the rear. The turret had a turret ring diameter of 95 cm, weighed 700 kg, and was armed with two Hotchkiss mle 1914 8×50 mm Lebel machine guns. The crew of the SRB consisted of three, with the commander sat in the turret. The turret was mostly a command post, and the purpose of its armament was to defend the tank against enemy infantry, while the hull gun would engage static fortifications. The driver sat to the left of the hull, and also operated as the hull gunner, which made him quite overtasked. The loader sat behind the 47 mm gun, on the right side of the hull.

Trials: The best impressions

The SRB prototype was trialed along with the three other Char de Batailles starting in Rueil, from May of 1924 to March of 1925. It should be noted that it was tried with a supply trailer designed by Schneider, which had a weight of one tonne and could carry 800 liters of fuel and seat eight men. This was a forerunner to a Schneider trailer which was offered and used on the first B1s in the 1930s.

The SRB is generally considered as the vehicle which performed the best during those trials. The internal configuration, which it shared with the SRA, with the hull gun pushed to the right of the hull, left the driver/gunner considerably less cramped and more comfortable than on the FCM and FAMH designs. The vehicle’s tracks were also praised. Their metallic and unitary nature left them a lot less worn out than the wooden pad tracks of all other prototypes. Most importantly, the Naedar system featured on the SRB was praised as by far the most effective way of accurately pointing the hull, far superior to the epicyclic transmission used on the SRA.

Conclusion – A deeply influential design on the future B1

Out of all the Char de Bataille prototypes manufactured, the SRB is arguably the one that had the most influence on the future Char B1.

While the SRA may at a first glance seem a little bit more similar to the final product, with its 75 mm hull gun, the SRB’s metallic tracks and Naeder systems were two major features of the B1 which were only featured on the Schneider design. The 47 mm naval gun may perhaps have had some influence as well. The second and third prototypes of the B1, in the early 1930s, were armed with 47 mm naval guns in a fully rotative turret, and the B1 and B1 Bis finally retained the 47 mm anti-tank gun as a feature of their design, albeit replacing the machine gun-armed turret of the Char de Bataille & first B1 prototype, and not the 75 mm hull gun.

Char de Bataille SRB specifications
Dimensions (L x w x h)	6.00 x 2.50 x 2.38 m
Ground clearance	0.41m
Weight	19,000kg
Engine	Renault six-cylinder producing 180 hp at 1,500 rpm
Maximum speed	18 km/h
Power-to-weight ratio (in hp/ton)	9
Fuel tanks	370 litres
Average hourly fuel consumption	20 to 35 litres
Range	125km
Suspension	Leaf springs
Trench crossing	2.50m
Crew	3 men (Commander/turret gunner, driver/gunner, loader)
Armament	2 turret-mounted Hotchkiss mle 1914 8 mm machine guns, 1 hull-mounted 47mm mle 1902 gun
Armor	30mm maximum

Sources

Tous les blindés de l’Armée Française 1914-1940, François Vauvillier, Histoire & Collection editions, p 42-43
GBM N°107 (January-February-March 2014), Histoire & Collections editions, “Les voies difficultueuses du char de bataille”, p 45-46, Stéphane Ferrard
Trackstory N°3 : Les chars B, Editions du Barbotin, p 5-7
Tank Archives: http://www.tankarchives.ca/2016/12/char-b-difficult-beginning.html
Char-français: http://www.chars-francais.net/2015/index.php/engins-blindes/chars?task=view&id=684
Ateliers de Construction de Rueil – Services des Etudes – Char B1 Bis – Notice sur la description et l’entretien des matériels
Wikimaginot (47mm mle 1902 gun): https://wikimaginot.eu/V70_glossaire_detail.php?id=1000280&su=Canon_antichar_de_47_mm_mod%C3%A8le_1902_-_47_mle_1902