Char B40

France (1939-1940)
Heavy Tank – Concept Only

When it comes to the various projects in development in France by 1940, the B40 often comes off as both one of the most potentially impressive, but also one of the most mysterious. The last evolution of the Char de Bataille/B1 family before the Armistice cut off the manufacturing arms of France’s military industry, very little is known about this last model which never got the time to jump beyond the drawing board to prototype stage or serial production. In fact, while we have clues to what the vehicle may have looked like, no views of the plans have even reached the modern age.

The unborn heir of the B1 Ter

By late 1939, the most advanced member of the B1 family in development by the French military was the B1 Ter, of which three prototypes were in construction – one by ARL, one by FL and one by FCM. An evolution of the B1 Bis, the B1 Ter reached a heavier weight of 36 tonnes. While it improved on its predecessor in some aspects – featuring a thicker armor protection and some amount of lateral traverse for the hull-mounted 75 mm gun notably – it failed to address some core issues to the design, such as, for example, the one-man turret. This was armed with a 47 mm SA 35, which was still very much decent by 1940, but would realistically become obsolete fairly soon, and with more powerful alternatives in existence in France.

As such, in either late 1939 or very early 1940, AMX and ARL, two of France’s leading design bureaus, particularly when it came to heavy designs, were approached to design a 40 to 42 tonnes heavy tank which would be given 80 mm of armor. While it would retain the hull 75 mm gun of the B1 Ter, it would swap the 47 mm SA 35 for one of the two more powerful 47 mm anti-tank gun availables by then, the 47 mm mle 1934 RF fortification anti-tank gun or the 47 mm SA 37 field anti-tank gun. AMX’s project would be designed on the base of an artillery-carrying chassis they were working on, resulting in the AMX Tracteur B. Part of the motivation behind AMX and ARL being asked to design this new tank was the belief of the commission tasked to work on the Char de Bataille program that the G1 program would not conclude in a vehicle being adopted for service, and that an alternative – potentially in the form of a new, more modern heavy tank – would be needed.

Meanwhile, ARL had been the leading bureau designing the B1 Ter, under the lead of engineer Lavirotte. To design their version of this new heavy tank, instead of taking a blank state, ARL’s design team would take their well-established B1 Ter design and improve upon it. The AMX and ARL pre-projects would both be presented and judged in the first trimester of 1940. This was merely weeks before the German invasion would come kicking in, and as such, the B40 could never really get any further than plans, though some components would apparently be mounted on ARL’s B1 Ter prototype for experimental purposes.

The rough lines of the B40

Information on the B40 is relatively scarce – the vehicle is mainly known through an article written by its lead designer, Lavirotte, in 1967. Though Lavirotte has gone fairly deep into the vehicle’s suspension design, engine and gearbox, he fails to mention some important aspects of the vehicle.

This is notably the case for the dimensions. The B40 was known to have been widened to an extent in comparison to the B1 Ter in order to accommodate a larger turret ring as well as wider tracks which would help spread the vehicle’s weight more evenly. At its widest, the B40 would have been slightly over 3.10 m, which was the size requirements for the SNCF (Société Nationale des Chemins de Fer – National Railway Company). In order to solve this issue, the large ‘tunnel’ mudguards for the tracks would have a retractable section, suggesting the vehicle was likely very close to this said 3.10 m requirement (for the sake of comparison, the B1 Ter was 2.73 m wide). The main reason to widen the vehicle to such an extent was to vastly expand the turret ring. At 1,280 mm, as on the B1 Ter, it could pretty much not reasonably be expanded further on a vehicle with a fighting compartment the width of the B1 Bis’ or B1 Ter’s. However, the turret ring was widened all the way to 1,680 mm on the B40.

Hull construction

The hull of the B40 was based on the B1 Ter but considerably expanded in terms of the elements that had been first introduced by this previous member of the B1 family.

The B1 Ter had introduced welding to a large portion of the hull’s construction. This was expanded on the B40, which almost entirely moved away from bolting to feature an almost entirely welded hull – a much more modern construction technique that would both quicken construction times and improve the structural resistance of the hull.

The armor layout was to be of 80 mm on the front and sides, and 60 mm to the rear. Additional 40 mm side plates would protect the suspension. The roof was 30 mm thick. The bottom of the hull also received a quite important thickness of 40 mm, as the B40 had been designed with mine protection in mind. This bottom would be constituted of the bottom of the hull itself and the bottom of the 40 mm plates protecting the suspensions, linked by plates inclined at 45°. However, the B40 would forfeit the ‘diamond-shaped’ angled sides, which, at 25°, were thought to provide little additional protection while making the design overcomplicated. The B40 would return to flat sides, similar to the B1 Bis, and likely re-introduce some other features from the B1 Bis (for example, a forward-opening door instead of the B1 Ter’s downward opening ‘drawbridge’ type side door)

The widening of the hull, performed for the sake of including a wider turret ring, would also allow for massively expanded fuel tanks on the B40. From 500 liters on the B1 Ter, these would be expanded all the way to 1,500 liters on the B40, which would massively expand the range of the tank. The engine which would have powered the B40 was a Talbot 500 hp turbo compressed engine, a very considerable upgrade in comparison to the B1 Ter’s 307 hp engine, which also equipped the B1 Bis. Despite the rising weight, the B40 would likely have been more mobile than its predecessor. The air intakes would have been located on top of the engine compartment, as on the B1 Ter. The tank was to use a gearbox installed perpendicularly to the tank’s axis, with six speeds but, thanks to inversion, also six reverse speeds, as well as a main and a secondary differential. Brakes for the tank were inspired by those found on heavy trucks. An immobilization brake acted on the main differential, and two smaller brakes acted on the secondary differential and could also be used when the tank would take a turn.

The widened hull would also likely have improved the conditions for the 3 crew stationed in the hull. In this regard, the vehicle was to remain similar to the B1 Ter. The driver would operate from a driving post of a similar design, and remain the gunner for the 75 mm gun. As on the B1 Ter, the 75 mm gun would have had some degree of lateral traverse in its mount. Interestingly, its servant would also be tasked with reloading the turret’s 47 mm gun from the hull itself. The radio operator remained as the third crew member.

As for the rotation of the hull, two alternative systems to the Naeder present since the SRB were considered for the B40. One, the T.A.H.V, was to be a hydraulic system of simpler construction, and was tested on a testbench, but not on a tank. The other, the B.N., was an electric machine and was actually experimentally mounted on a B1 Bis. In comparison to the Naeder system, it required no radiator, far less maintenance, and required less physical effort when rotating the hull. However, while with the Naeder, the tank would rotate at the same time as the steering wheel associated with the system, with the B.N, the driver would first have to fully rotate the steering wheel, and then progressively rotate it back for the vehicle to rotate with it, due to delays in the transmission of commands. This system was eventually judged to be inferior to the Naeder, and the B40 would retain a simplified and improved version of the classic hydraulic steering system.

Oleo Pneumatic suspension

In order to save weight, the B40 was to replace the suspension used in the previous vehicles with a new oleo-pneumatic one. It would nonetheless retain some elements of the previous suspension, notably the three tender wheels at the front, as well as one at the rear. The size of the road wheels appears to have been retained in general.

What differed were the suspension arms. The B40 got rid of the B1 Bis’ ensemble of three large, coil-spring mounted bogies, each containing two smaller bogies that held two road wheels. Though a similar number of bogies/road wheels appears to have been retained, these instead used a new oleo-pneumatic system. Each bogie group would contain a large cylinder. A piston would be moved by the main boogie, and itself be linked to an additional piston, with an oil-filled reservoir between the two. Between these two pistons, the suspension would also feature a “diaphragm” which would allow for smooth movements. Between the second piston and the cylinder was a “mattress” filled with compressed air, with a variable quantity of air present, which would then act on the boogie.

The tender wheels, originally mounted on leaf springs, also adopted an oleo-pneumatic system, being linked to a piston containing a variable mass of compressed air.

This system was trialed on the ARL B1 Ter prototype. The vehicle could only run for 10 hours before the Armistice but appears to have worked properly with this suspension system.

The B40 would have adopted widened tracks, going from 50 to 60 cm, in order to better spread the vehicle’s weight. The vehicle would have retained large ‘tunnel-like’ track guards on top of the track run. Oiling ports for the B40 would have been located in the same places as the B1 Ter.

A more than one man-turret, at long last

One of the most significant improvements brought to the B40 was the turret. Up to this tank, tanks of the Char de Bataille program had always retained a one-man turret – from the machine gun-armed Schneider turrets of the SRA and SRB, to the cast, 47 mm armed APX 1 and APX 4 of the B1 and B1 Bis, to the welded ARL 2C of the B1 Ter.

The B40 would retain a welded turret. Whatever little information there is on the turret indicates that, generally, it would be roughly similar to the ARL 2C. However, it would be vastly enlarged, with a turret ring expanded from 1,280 mm to 1,680 mm. This would accommodate two major improvements. The first was a far more powerful anti-tank gun in the form of the 47 mm modèle 1934 RF, originally designed as an anti-tank gun for the Maginot Line. The 47 mm mle 1934 was an L/50 gun that fired an armor-piercing capped shell with a magnesium cap. This was a quite heavy 47 mm shell, weighing in at 1.670 kg and propelled by a 610 grams charge of powder, giving it a muzzle velocity of 880 m/s. At an incidence of 30°, it would penetrate 77 mm at 500 m and 56 mm at one kilometer.

Perhaps even more important than this powerful anti-tank gun was the move away from the one-man turret, with the B40 finally accommodating a second crew member in the turret, the gunner. The loading functions would reportedly not be assumed by the commander but by the 75 mm loader operating from the hull. Such a configuration was still lackluster in comparison to the pure 3-men turret of the German Panzer III and Panzer IV, but was a massive improvement from previous one-man turrets, which left the commander massively overburdened, particularly with a tank as complex as a Char de Bataille, which also contained a hull gun.

The B40 as of May 1940

As the project was before the campaign of France, the B40 would have been yet another incremental improvement in the Char de Bataille family of designs. As the B1 Ter and B1 Bis before it, it would have improved significantly on the previous models. However, one could still claim the design would not have resolved all the previous issues, or have been ideal. Notably, the dual gun configuration, which was retained, would not be optimal, and the vehicle, though now simpler to construct due to the liberal use of welding, would still be heavy and unreliable.

The Char de Bataille they should have built from the start: A turreted 75 mm

The B40 was not to be frozen entirely in its May of 1940 shape though. It is one of the few known instances of an existing French project being amended during the course of the campaign of France itself, using feedback from the units engaged at the front.

By late May 1940, the four DcRs (Division Cuirassée de Réserve – ENG: Reserve Armored Division, with the reserve part indicating the divisions were to be used in exceptional breakthrough operations as a strategic reserve, rather than being divisions formed of reserve servicemen) equipped with the B1 Bis had been heavily engaged in the Campaign of France. In some cases, they saw their B1 Bis fleets almost entirely eliminated. Though the tanks could occasionally prove a significant opponent to their German adversaries, those first combat experiences showed some core issues of the Char de Bataille series of tanks, which the French Army had been effectively blind to up to this point.

One of the major requests of the B1 Bis’s crews was that the 75 mm would have proved much more useful in the turret. Even with the advanced Naedar steering system, a dual gun configuration proved less than ideal, and the solution clearly appeared to have been a weapon that could effectively combine the roles of both the 75 mm and 47 mm – fight both tanks and infantry or fortifications – in a turret. Luckily, such weapons were already in existence within the French Army, notably the 75 mm APX 30 calibers gun featured in the SaU 40 and ARL V39 prototypes as well as a variety of other projects.

The solution that was swiftly devised by ARL’s engineers in late May and early June appears to have been to simply take the turret of one of their projects which would have mounted a turreted 75 mm APX gun, the ARL Char de Forteresse. Its ARL 4 turret, though quite tall, had a two-man crew and a 1,680 mm turret ring, like the turret which was to be mounted on the B40. With its armor thinned from the Char de Forteresse’s 120 mm to the B40’s 80 mm, it could fairly reasonably be mounted in the tank and provide multi-purpose firepower which would prove superior to the dual-gun configuration that had been retained up to this point. In the meantime, the space gained by the elimination of the hull 75 mm gun could potentially be used to accommodate yet another fuel tank, or more ammunition stowage. Without a hull 75 mm gun, the driver would prove vastly less overburdened and require less training, as he had no gun to act as a gunner for. The gun’s servant could also fully concentrate on the role of being a hull-located loader for the turreted main gun, or be removed outright to gain further space.

Outside of a heightened silhouette and likely gaining a couple of tonnes due to the larger turret, this improved B40 only brought improvements to the previous design, and one could argue that the solution of a turreted 75 mm gun should have been adopted for the Char de Bataille family of vehicles a lot earlier. This is obvious with hindsight, but a lot less so when you consider that whether a 75 mm gun both powerful enough to defeat armor and compact enough to reside in the turret of a vehicle of this size could be developed was uncertain for a long time.

The Char de Bataille is not yet lost: Lavirotte’s work under occupation

By the time the 75 mm-turret B40 was being studied though, it was way too late. The 1940 campaign ended in a hard-fought but disastrous defeat for France, with the country occupied by German forces and divided into a German-occupied zone and the Free Zone of the Vichy Regime in the south, controlled by a French government under strict military limitations.

These limitations being strictly enforced by all of France’s Army men and engineers were little more than a pipe-dream though. Quickly after the armistice, a secret service for the stockpiling of material as well as the refitting of incomplete armored vehicles and eventually the production of new ones would be formed as the CDM (Camouflage du Matériel – Material Camouflage). The CDM’s own design bureau would produce two different vehicles, the Panhard 178 CDM and CDM armored car. At the same time, it would work to provide Lavirotte and the remaining members of his team with resources to continue studying tanks that could be manufactured abroad or after the liberation of France. The most mature work to emerge out of this bureau would be the SARL 42. However, Lavirotte would continue work on the B40 and some of its elements, with the idea of a 30-tonnes tank which would take some elements of the B40, such as the oleo-pneumatic suspension and Talbot turbo compressed engine, would emerge. After the liberation of France, these early studies would evolve into the first new French post-war tank design, the ARL 44 – the direct heir of the mysterious B40.

Conclusion – The missing link

The B40’s obscure status – far more than any known member of the Char de Bataille family, to the point no imagery of the vehicle survives – has led to it being wildly fantasized about. This, coupled with a misinterpretation of a page of François Vauvillier’s Tous les blindés de l’Armée Française 1914-1940, which showed the B40 on the same page as the ARL B1 Ter along with a photo of the ARL B1 Ter hull in construction, has lead some to actually believe a B40 prototype was in construction or finished by May 1940, which was not the case. Nothing but plans of the vehicle and some elements tested on the B1 Ter ever existed, and whatever did likely disappeared along with the FL, ARL and B1 n°101-based B1 Ter prototype when their ship was sunk by German aviation in the estuary of the French river Gironde in June 1940.

Nonetheless, the B40 remains a significant member of the Char de Bataille family. It is effectively the link between the pre-war designs formed by the B1, B1 Bis and B1 Ter, and their final evolution, the ARL 44 of the first post-war years, France’s first new tank, still studied under the lead of the same Lavirotte who led work on the B1 Ter and B40.

B40 specifications (original project)
Weight	40 to 42 tonnes
Engine	Talbot 500 hp turbo compressed engine
Transmission	6 forward + 6 reverse
Track width	60cm
Crew	5 (Commander, gunner, driver/hull gunner, loader for both pieces, radioman)
Main armament	75 mm SA 35 infantry support gun; 47 RF mle 1934 anti-tank gun
Secondary armament	Very likely coaxial MAC 31E 7.5 mm machine gun
Hull armor	80 mm (front and sides) 60 mm (rear) 40 mm (floor, suspension protection) 30 mm (roof)
Turret armor	Unknown, but likely same layout as the hull
Fuel tanks	1,500 liters

Sources

Char d’assaut & Blindés n°13 to 15, Lavirotte, 1967
GBM n°111, January-February-March 2015, “Les derniers Chars B”, Stéphane Ferrard, pp 83-96, Histoire & Collections editions
Notice provisoire sur les matériels de 47 et de 37 de casemate mle 1934 du 4 mars 1939 via Wikimaginot
Trackstory n°13: Le Char B1, Editions du Barbotin, Pascal Danjou
Wikimaginot