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The FCM 36 was developed from 1934 onwards as part of a programme to replace the obsolete Renault FT. As it was more expensive to produce than competing designs, only a limited production of a hundred was authorised. It featured some advanced technologies such as a diesel engine and an extensive use of welded sloped armour.

In 1933 the Hotchkiss company proposed to build a cheap mass-produced light infantry tank. In reaction to this proposal the French Army invited the whole of French industry to offer alternative designs. In the end three of the competing prototypes would be taken into production: the Hotchkiss H35, the Renault R35 and the FCM 36.

The Forges et Chantiers de la Méditerranée (FCM), located at Toulon, had some previous experience with tank production as it had constructed the ten giant Char 2C tanks in 1921 and had been involved in the development of the Char B1. Engineer Bourdot, who had designed the suspension of the Char B, was ordered to create a modern tank design taking full advantage of the large electro-welding capacity of the wharf. In March 1934 he presented a wooden mock-up that was approved by the Army. On 2 April 1935 the prototype was delivered to the Commission de Vincennes, with a turret equipped with two machine-guns. The commission was quite impressed by the vehicle, especially because of its welded sloped armour and the use of a diesel engine promising a good range. It was a bit heavier than the specified nine metric tons at 10,168 kilogrammes. However the prototype was untestable because of mechanical problems. After the first evaluation had been finished on 9 June it was sent back to the manufacturer.

In fact FCM had not tested the prototype itself yet; this was now done and many shortcomings became apparent. As a result, the vehicle was completely redesigned with a new and lighter hull and turret configuration, suspension and track. The roof of the engine compartment was now bolted on to ease replacement. On 10 September it was again sent to Vincennes only to be sent back on 23 October to have its suspension reinforced. On 19 December it returned to be tested until 14 May 1936. It was then approved on the provision that the armour would be thickened from 30 to 40mm, according to the new specifications. This was done by welding an appliqué 10mm armour plate on top of the main armour, a feature maintained for the production vehicles. The prototype was now brought to the attention of the Commission d'Infanterie, who declared on 9 July that it was the best of all competitors, especially since it had been proven on 17 June to be completely gas-proof, a unique quality that was considered a very desirable feature at the time.

The FCM 36 was a small vehicle, 4.46m long, 2.20m high and 2.14m wide, with a crew of two. It had a weight of 12.35 metric tons. The armour consisted of many panels electro-welded together into an pyramidal shape to avoid shot-traps and fully implement the principle of sloped armour. Such a configuration was unique at the time. This included the upper track run and the suspension units, protected by zig-zag armour plates. The engine deck is the only armour which is bolted as this enables easier access to the engine. As the armour is of good quality, the 40mm thickness angled at 30 to 45 degrees from the vertical, renders an equivalence of about 45–55mm, enough to regularly defeat the standard anti-tank guns of its day, even when the gun was ideally positioned. The reclining armour implied that more raking shots would quickly start to deflect. The type was the only actually produced French tank of the period that featured a diesel engine, which gave the vehicle a superior range of 225 kilometres from a fuel tank of 217 litres.

In other aspects, it conformed to the French design standards. French tanks were usually slow compared to their German, British or Soviet counterparts. The V-4 91hp Berliet diesel allowed for a top speed of just 24 km/h (15 mph). The suspension was accordingly simplistic, consisting of eight road wheels per side sprung by eight vertical coil springs. The tank could cross a two metres trench and climb a 70cm obstacle or an 80% slope. Also very limited is the armament: apart from the 7.5mm Châtellerault MAC31 machine gun, the standard short L/21 37mm SA 18 gun was fitted, a cannon with very poor anti-armour capacity.

The Hotchkiss H35 or Char léger modèle 1935 H was a French cavalry tank developed prior to World War II. Despite having been designed from 1933 as a rather slow but well-armoured light infantry support tank, the type was initially rejected by the French Infantry because it proved difficult to steer while driving cross-country, and was instead adopted in 1936 by the French Cavalry arm

In 1926, it had been decided to provide armour support to the regular infantry divisions by creating autonomous tank battalions equipped with a light and cheap infantry tank, a char d'accompagnement. For this role at first the Char D1 was developed which type however, proved to be neither particularly light nor cheap. In 1933, the Hotchkiss company under its own initiative presented a plan to produce a lighter design—this was made possible by the application of a new technology to produce cast steel sections to construct an entire hull. On 30 June 1933, this proposal was approved by the Conseil Consultatif de l'Armement. On 2 August 1933 the specifications were issued: a weight of 6 long tons (6.1 t) and 30 mm (1.2 in) armour protection all around. Three prototypes were ordered from Hotchkiss, but the French industry as a whole was also invited to provide alternative proposals for a nouveau char léger.

This allowed the Renault company to beat Hotchkiss in delivering the first prototype, which later was developed into the Renault R35. On 18 January 1935, the first Hotchkiss prototype, not yet made of armour steel, was presented to the Commission d'Expérience du Matériel Automobile (CEMA) at Vincennes; it was a machine gun-armed tankette without turret. It was tested until 4 March 1935, when it was replaced by the second identical prototype to be tested until 6 May. Both had to be rejected because new specifications had been made on 21 June 1934 that increased the desired armour thickness to 40 mm (1.6 in). On 27 June 1935 the commission approved the type on the provision that the necessary changes would be made. On 19 August the third prototype was delivered, equipped with a cast APX turret and featuring a redesigned hull; it was tested until 20 September and accepted.

On 6 November 1935 a first order was made for 200 vehicles. Though it should have been completed between July 1936 and July 1937, the first production vehicle was in fact delivered on 12 September 1936. A first additional order had already been made of 92 on 7 September 1936, to be completed in November 1937. A third one of 108 vehicles followed on 23 January 1937, to be completed in September 1938. These vehicles had the series number 40000 to 40400.

The first series vehicle was again extensively and intensively tested until 4 December 1936. The testing soon showed that its cross-country handling qualities were unacceptably poor; it proved impossible to safely steer the vehicle on a uneven surface, posing an extreme danger to nearby friendly infantry. The Infantry therefore initially rejected any further procurement. Eventually, in 1937, it decided to accept only the last hundred tanks to equip just two battalions with the type: the 13e and 38e Bataillon de Chars de Combat.

For political reasons however, stopping production of the tank was unacceptable. As a result the first three hundred vehicles of the production run were offered to the Cavalry, which was forced to accept them because it would not have been granted a budget for other tanks anyway.[1] As the cavalry units would be making more use of the road network and of mounted infantry, its cross-country handling problem was of less consequence. The H 35 was, at 28 km/h (17 mph), also somewhat faster than the Renault R35, which was capable of 20 km/h (12 mph), although in practice its average speed was lower than that of the R 35 because of its inferior gear box.

The Hotchkiss H35 was 4.22 m (13 ft 10 in) long, 1.95 m (6 ft 5 in) wide and 2.13 m (7 ft 0 in) tall and weighing 10.6–11.4 t (10.4–11.2 long tons). The hull consisted of six cast armour sections, bolted together: the engine deck, the fighting compartment, the front of the hull, the back of the hull and two longitudinal sections left and right forming the bottom. The hull was made water-tight by cementing these sections together with Aslic, a product based on tar mixed with lime. The casting allowed for sloped armour, avoiding shot traps, to optimise the chance of deflection but the protection levels did not satisfy the Infantry. Maximum armour thickness was not the specified 40 mm (1.6 in) but 34 mm (1.3 in). There were persistent quality problems, worsened by the fact that many subcontractors had to be used: at first the armour was made much too soft; when hardness was increased it became brittle and full of bubbles and hence weak spots.

There was a crew of two. The driver sat at the right front, behind a large cast double hatch and next to the combined gearbox and steering unit. Behind him was a round escape hatch in the bottom of the hull. Driving the vehicle was very hard work. The Hotchkiss lacked the Cleveland differential ("Cletrac") of its Renault competitor, and it responded unpredictably to changes of direction. The brakes could not sufficiently compensate for this, being too weak, especially when driving down-slope. No less troublesome was the gearbox: it was difficult to engage the highest fifth gear and so the theoretical top speed of 28 km/h (17 mph) was rarely reached. There was one reverse gear. The inevitable rough handling of the tank by the driver resulted in much wear and tear. Mechanical reliability was poor.

The suspension consisted of three bogies per side—each formed of two bell cranks arranged as "scissors" with springs at the top. Each bogie carried two rubber-rimmed wheels. The first ten production vehicles, which can be considered as forming a separate pre-series, had curved bogie sides; in later vehicles the bogies had straight sides. The bogies superficially resembled the R35 type, but used horizontal helical springs instead of rubber cylinders. The sprocket was at the front, the idler—which itself was sprung to automatically control tension—at the rear. There were two top rollers.

The rear of the hull formed an engine room, separated from the fighting compartment by a fireproof bulkhead. The tank was powered by a 78 hp six-cylinder 86 x 100 3485 cc engine which was on the left of the engine compartment. A 160-litre fuel tank on the right, combined with a twenty litres reserve reservoir, gave a range of 129 km (80 mi) or eight hours on a varied terrain. The engine was cooled by a centrifugal pump. Also a cooling fan drew air through the radiator and was also expected to cool the fuel tank. The trench-crossing capacity was 1.8 m (5 ft 11 in), the wading capacity 0.85 m (2 ft 9 in). On hard soil a slope of 75 percent could be climbed, on soft soil of 55 percent. Maximum tilt was 50 percent. Ground clearance was 37 cm (15 in).

The APX-R turret was the same standard type as used on the R35 and R40 tanks, made of 40 mm (1.6 in) cast steel and armed with the short 37 mm SA 18 gun, which had a maximum armour penetration of only 23 mm (0.91 in). Traverse of the turret was with a handwheel. The commander sat in a saddle suspended from the turret.

The tank carried about 100 rounds for the gun, and 2,400 rounds for the coaxial 7.5 mm Reibel machine gun – the 37 mm ammunition was racked on the left hand side of the hull, the 7.5 mm ammunition on the right side in fifteen circular magazines with 150 rounds each; with usually an additional magazine on the machine-gun itself. The turret had a rotating cupola with a PPL RX 180 P visor but there was no hatch in the cupola though its top could be lifted a bit for better ventilation. Apart from the cupola there were protected vision devices, a binocular periscope and diascopes, to the front beside the gun and to each side. For access there was a hatch at the back of the turret. When opened, the commander could sit on it for better observation, but this left him very vulnerable and slow to reach the gun. The alternative was to fight closed-up, observing through the vertical slits or the visor of the hatchless cupola. The Cavalry liked neither this arrangement nor the weak gun. The latter problem was lessened by enlarging the breech so that special rounds with a larger charge could be used. This increased muzzle velocity to about 600 m/s (2,000 ft/s) and maximum penetration to about 30 mm (1.2 in). Only a small number of the tanks, and limited to the Cavalry, were modified however, because it greatly increased barrel wear. In the spring of 1940 the original diascopes of the Chrétien type were gradually replaced with episcopes, offering more protection.

Though its name might suggest otherwise, the AMR 33 was not a scout vehicle and mostly was not equipped with a radio set. The AMR 33s were intended to form a large mass of light tanks, preceding the medium types into battle.

To counter the threat posed by the massive Soviet arms build-up since 1928, the year Joseph Stalin took power, the French government on 4 July 1930 conceived the plan to form a projection force capable of assisting its allies in the Cordon sanitaire. This force would have to consist of five motorised infantry divisions and the five existing cavalry divisions, one brigade of each of which would have to be motorised. The plan called for the introduction of many specialised vehicles, among which was an Automitrailleuse de Cavalerie type Reconnaissance (AMR), specified on 16 January 1932 as a vehicle of three tons, armed with a light 7.5 mm machine gun and having a range of 200 kilometres. It should have a crew of two, have an average terrain speed of 35 km/h and an armour base of 9 mm. Automitrailleuse was then the generalised term for any light armoured fighting vehicle armed with a machine gun. The Cavalry then used only wheeled vehicles because the tanks were too slow but the designation remained when tracked vehicles entered service. Although the name might suggest otherwise, an AMR was not a specialised reconnaissance vehicle but a skirmisher without a radio. The gathering and reporting of information was the task of an AMD (Automitrailleuse de Découverte).

In anticipation Louis Renault had early November 1931 already begun to design a tracteur léger de cavalerie type VM based on his Renault UE tractor. On 12 November the first drawings were examined and rejected because the vehicle in its proposed form was much too cramped. A larger hull was clearly necessary but Renault was hesitant to invest in it without the prospect of a possible order. On 21 November he was asked by the Section Technique de la Cavalerie to provide a tankette version of his Renault UE to test the feasibility of a tracked AMR-concept. Being hereby informed of the general outlines of the specifications, he sent on 22 December a representative to supreme commander Maxime Weygand to lobby for a Renault AMR. Weygand informed him that it had informally been decided to procure the AMR Citroën Kégresse P 28, a half-track made by Renault's competitor Citroën. After much deliberation however the General that very day committed himself to take a Renault tank into consideration.[citation needed]

That commitment being secured, Renault hastily designed a larger model, a wooden mock-up of which was presented in March 1932. Based on it an order was made on 20 April of five prototypes for a price of 171,250 FF per vehicle, to be delivered in September before the start of the autumn Champagne manoeuvres. The Cavalry saw this as a pre-series to obtain a platoon to be used for its very first trials with a mechanised unit. Renault however decided to provide each with a different suspension type, to lower the risk that his design would be found wanting. All were generally based on the Carden Loyd type that Renault had simply copied for his Renault UE – without paying any licence rights – and used the standard Renault Reinastella engine.[10] As there simply wasn't time to fully develop all types before the autumn, in July the five vehicles, with military registration numbers 79756 to 79760, were delivered with the simplest one: two leaf springs on each side didn't spring the suspension units, they were the suspension units. In September the tanks were united in the first French Cavalry mechanised unit ever: the experimental Détachement Mécanique de Sûreté. The experience showed that they were very agile, but also noisy, poorly balanced and lacking sufficient range; unsurprisingly, the crew was always in for a bumpy ride.

After the exercise they were sent back to Renault, who shortly afterwards submitted three types for evaluation to the Commission d'Expériences du Matériel Automobile at Vincennes: prototype 79758, still with the original suspension, 79759 with added internal hydraulic dampers and 79760 with a fully new suspension consisting of a central bogie with a leaf spring and wheels at the front and the back connected to two horizontal helical springs. In November and December 1932 the "Commission de Vincennes" tested them, using as reference changed specifications determined on 10 June 1932.[14] They were found to have a sufficient speed (56.25 – 60 km/h), but an insufficient range of 166 - 188 kilometres and to be too heavy with a weight of 4.8 tons. On 8 December it was decided to abandon the unrealistic three ton weight limit and install larger fuel tanks and heavier armour, 13 mm thick; the vehicles were again sent back. In April 1933 Renault submitted two types, fitted with 0.5 ton weights simulating an up-armouring from nine to thirteen millimetres maximum: 79758 rebuilt with a horizontal rubber spring suspension and 79757 fitted with a suspension derived from that of 79760, but now with a central vertical spring and the casings of the horizontal springs filled with oil to make them act as dampers. They were tested until June 1933 and, against the strong advice of Renault favouring the rubber springs, on 6 June a production was ordered for prototype 79757 as the AMR Renault modèle 1933 or AMR 33.

The AMR 33 is a very small vehicle, 3.5 m (11 ft 6 in) long, 1.64 m (5 ft 5 in) wide and 1.73 m (5 ft 8 in) tall. It weighs only 5.5 metric tonnes; the unloaded weight of the hull 4.5 tonnes. The eight-cylinder 84 hp 4241 cc Renault Nervasport[21] 24 CV engine allows for an official maximum speed of 54 km/h (34 mph) – the Renault export brochure claimed 60 km/h (37 mph) and an off-road speed of 45 km/h (28 mph). A Cleveland differential was used; there were four forward and one reverse gears. A fuel tank of 128 L (28 imp gal) allowed for a range of 200 km. The tracks were 22 centimetres wide. It had a wading capacity of sixty centimetres; could cross a trench 1.4 m (4 ft 7 in) wide, or climb a 45 cm (18 in) vertical obstacle or a 50% slope.

Details of the turret

The development plan of 1926 foresaw the introduction of a char d'accompagnement, a cheap mass-produced light tank to replace the Renault FT of World War I vintage, to make it possible for the standard infantry divisions to execute combined arms infiltration tactics, seen as the only viable method of modern offensive warfare left for non-motorised units. The French army did not have the means to motorise more than a few select divisions. In 1930 this plan was replaced by a new one, giving more precise specifications. The first tank to be developed to fulfil its requirements, the Char D1, proved to be neither cheap nor particularly light. In 1933, Hotchkiss offered an alternative solution, the later Hotchkiss H35. For political reasons this proposal was turned into the Plan 1933 and the whole of French industry was in August 1933 invited to propose possible designs. Fourteen companies responded (among which Delaunay-Belleville) and five submitted a prototype: Hotchkiss itself, the Compagnie Général de Construction des Locomotives, APX, FCM and of course France's prime tank producer: Renault. Fearing that his rival Hotchkiss might well replace him as such, Louis Renault hurried to finish a vehicle; construction was soon in such an advanced stage that the changes in specification issued on 21 June 1934, to increase armour thickness from 30 to 40 mm, could not be implemented. On 20 December 1934 Renault was the first to deliver a prototype, with the project name of Renault ZM, to the Commission de Vincennes.

In the spring of 1935 this vehicle was refitted with heavier armour and a standard APX turret, attached by the Atelier de Rueil between 18 and 25 April. The prototype was still being tested when international tensions increased due to German re-armament. This prompted an urgent demand for swifter modernisation of the French tank fleet. The ZM was to be put into production immediately. On 29 April 1935 an order of 300 was made, even before the final model could be finished, at a price of 190,000 French franc per hull (unarmed, without the engine and turret, the overall export price was ca. 1,400,000 francs in 1939, that is ca. 32,000 dollars by 1939 standards). The first series production vehicle was delivered on 4 June 1936 and had to be extensively tested again as it was different from the prototype.

To save time, Renault based the suspension and running gear on that of the AMR 35 that was designed for the cavalry. It had five wheels at each side, fitted with horizontal rubber-cylinder springs, like the AMC 35.

The hull, with a length of 4.02 m, consisted of three cast modules, with a maximum armour thickness of 43 millimetres, that were bolted together. Total weight was 10.6 metric tonnes (9.8 tonnes without fuel and ammunition). The bottom module carried on each side an independently sprung front wheel, two bogies and the driving sprocket at the extreme front. The final drive and differentials were housed at the right in the nose module. It was steered through a Cletrac differential with five gears and by engaging the brakes. The driver was seated somewhat to the left and had two hatches. The Renault V-4 85 hp engine was to the right in the short rear with the self sealing 166 litre fuel tank at its left. It rendered a road speed of 20 km/h and a range of 130 km. Cross-country speed did not exceed 14 km/h and the fuel consumption totaled 212 litre/100 km. From 1940 onward they were fitted with AMX tails to help in trench crossing.

The cast APX hexagonal turret had a 30 mm thick domed rotatable cupola with vertical vision slits (the highest point of 2.13 m) and had to be either hand cranked or moved about by the weight of the commander, the only other crew member. There was sometimes unofficially a seat installed for him but he most often stood. The rear of the turret had a hatch that hinged down that could be used as a seat to improve observation. The earliest vehicles were fitted with the APX-R turret (with the L713 sight) mounting the short Puteaux 37 mm L/21 SA18 gun (the first batches were removed from Renault FT tanks which were then rebuilt as utility vehicles) and the 7.5 mm Châtellerault fortress machine gun. The cannon had a very poor armour penetration: only 12 mm at 500 metres. Afterwards the APX turret with the same cannon but the improved L739 sight and the standard Châtellerault 7.5 mm MAC31 Reibel machine gun was used because of delivery delays of the original weapon. There were also so many delays in the production of the turrets that after the first 380 hulls had been produced in 1936 and only 37 could be fitted with a turret, production was slowed down to 200 annually. The 7.5 mm machine gun's spent cartridges (from a total of 2,400) went down a chute through a hole in the floor. The tank carried 42 armour piercing and 58 high explosive rounds.

The R 35 at first had no radio, except for the second battalion of the 507e Régiment de Chars de Combat (of Charles de Gaulle), but the R 40 had the ER 54 installed. However, this added to the already heavy task load of the commander, who also acted as gunner and loader.

The three prototypes were, among others, fitted with turrets of the Renault FT during a mock-up. The production models of the first series had the APX-1 turret, armed with a short 47mm SA34 tank gun. The second series used the much more powerful 47mm SA35 tank gun; from March 1940 this was retrofitted to a number of the older vehicles, despite a parallel project to rebuild them as flamethrower tanks.

In 1937 the type equipped one tank battalion, which was considered an elite unit, as part of Charles de Gaulle's regiment. It was well-trained in the use of advanced tactics, including the use of radio-sets. In 1940 the effectiveness of this unit had much diminished, because of the worn-out state of its tanks, aggravated by the decision to raise three autonomous tank companies with the new vehicles, even though insufficient trained crews were available.

At the same time the Char D1 was ordered, a plan was made to develop a more modern tank. The Char D1 had already departed from the pure infantry support concept and evolved from a light into a medium tank, capable of fighting enemy armour; this made it the obvious candidate to be quickly changed into a lighter alternative for the Char B1 battle tank, needed because the latter type was in danger of being forbidden by an expected armaments limitation treaty under the auspices of the League of Nations, imposing an upper weight limit of twenty metric tonnes for armoured fighting vehicles.

The Direction de l'Infanterie proposed on 23 January 1930, in a letter to the ministry of defence, to build a better armoured tank, using 40 mm plate, that nevertheless would be swifter at 22 km/h by fitting a 120 hp engine. The weight however should rise only from 14 to 15.5 metric tonnes, made possible by using welded instead of riveted armour plate. On 14 April the plan was approved and in May Louis Renault was contacted, who agreed to develop this type as the Char D2, together with a colonial tank, the Char D3, which would closely resemble its sister project.

To introduce the new welding technique entailed hiring foreign experts, which was very expensive. Renault insisted that the costs would be paid in advance by the French Army, which however had no corresponding budget available. On 8 December 1931 the deadlock was broken by a new agreement: Renault would first build a prototype with a riveted hull, the Renault UZ, which was delivered in April 1932. First the type was tested in Rueil; in May 1933 field tests were carried out by 503e RCC. The type was accepted for production, which decision was affirmed by the Conseil Consultatif de l'Armement on 12 December 1933.

At that moment however, Germany had just left the League of Nations altogether, making the limitation talks irrelevant, from which then France retired also. Existing plans to produce 750 Char D2s, 150 per year for the period 1935–1939, (six hundred to equip twelve battalions and 150 as a matériel reserve) were immediately reduced. On 14 January 1934 the High Command confirmed only the plan of a first production order of fifty. All these decisions were taken on the basis of experience gained with the riveted prototype, though it was well understood that from it no firm conclusions could be drawn on the quality of the intended welded type.

Meanwhile, two welded prototypes had been ordered in December 1932. These were finished in August 1933, but only delivered in November. From December 1934 till the summer of 1935 the Commission de Vincennes used the three available prototypes to test different engine configurations. The riveted hull was equipped with a 120 hp petrol engine; the other two with diesel engines. These were rejected in favour of the petrol engine even though its combination with the intended welded hull had not yet been tested.

Nevertheless, on 29 December 1934 the order of fifty hulls was granted to Renault, at a price of 410,000 French Francs per piece. The turrets were produced separately. First the ST3 turret (Schneider Tourelle 3) had been tested in 1933; then the ST2, at the time seen as a possible standard turret for all heavier tanks, was considered but finally a choice was made to use the APX1, originally developed for the Char B1, costing ₣ 200,000. This turret brought the unit price to ₣ 610,000. The fifty vehicles were only delivered from May 1936.

Due to this delay a planned second order, to be made in 1935, of a hundred, to bring total production to 150 was cancelled. It had been assumed that the lighter Char D2 could be quickly produced as an interim type, to speed the formation of the first Infantry armoured division of the Infantry.

In essence the Char D2 was an improved Char D1. The different turret type used, increased its height somewhat to 266.6 centimetres; the hull was 175.5 centimetres high. The length of the hull, without tail, was 546 centimetres; its width was reduced to 222.3 centimetres through the use of a narrower track, 35 centimetres wide. The suspension was largely identical but the top rollers, to which a tension wheel was added, were placed somewhat higher to prevent track resonance, a persistent problem with the Char D1. The armour plate covering the three vertical coil springs consisted of six instead of eight panels; mud-chutes were added below each top roller. There were three bogies per side, each with four road wheels, a coil spring and two shock absorbers. In front, and at the back below the sprocket, there was a tension wheel with its own damper; identical to the road wheels proper they brought the total number of such wheels to fourteen. Another change was the fenders with large stowage bins that gave the false impression of being part of the main armour.

The production vehicles used far less welded sections than at first intended. To reduce the price, Renault opted to implement a novel construction technique, using large flat screws, serving both as bolts and, applied heated, as rivets, attaching the main armour plates to each other by means of thin connecting steel strips. This way no internal girders, forming a real chassis, were needed. The armour plates were 40 mm thick.

Like with the Char D1 there was a crew of three, but the radio-telegraphy operator sat to the right of the driver instead of the commander, and the antenna, of the ER52 set, has been moved to a position next to him. To make room a hull machine-gun was absent. This new configuration had been demanded to create a roomier fighting compartment. Two command vehicles, series numbers 2016 and 2049, had a second antenna on the left to serve their ER51 long range set. The engine power was increased considerably to 150 hp[3] by installing a Renault V-6 9.5 litres motor, but as the weight increased to 19.75 (just below the twenty tonne limit) instead of the intended 15.5 metric tonnes, the gain in maximum speed was only to 23 km/h. The gear box had four speeds. Four fuel tanks together holding 352 litres allowed for a range of a hundred kilometres. The wading capacity was 120 centimetres, a trench of 210 centimetres could be crossed, an obstacle eighty centimetres high or a slope of 50% climbed. The hull had a fixed 7.5 mm machine-gun low in the glacis on the right side.

The SOMUA S35 was a French cavalry tank to equip the armoured divisions of the Cavalry, it was for its time a relatively agile medium-weight tank, superior in armour and armament to its French and foreign competitors, such as the contemporary versions of the German Panzer III medium tank. It was constructed from well-sloped, mainly cast, armour sections, that however made it expensive to produce and time-consuming to maintain.

The design of the SOMUA S35 comes from the changed specifications of 26 June 1934 for an Automitrailleuse de Combat (AMC) issued for cavalry use. These called for a much heavier design than had been originally specified in 1931. The new type had to be immune to contemporary anti-tank guns.[1] By 17 May the Army had already contacted a subsidiary of Schneider et Cie — the Société d'Outillage Mécanique et d'Usinage d'Artillerie (SOMUA) based at Saint-Ouen — to build a prototype. The company accepted this proposal on 16 July and construction began on 12 October 1934. The prototype, with the name AC3, was ready on 14 April 1935. It was tested from 4 July until 2 August 1935. Then a pre-series of four was produced of an improved type, the AC4, to be tested until 27 January 1938. These first vehicles had the standard APX1 turret, fitted with the short 47 mm SA 34 gun. On 25 March 1936, the AC4 design was accepted as the standard medium tank of the French Cavalry with the official name Automitrailleuse de Combat modèle 1935 S (AMC 1935 S), when a first order for fifty was made. The tank was then more commonly known as SOMUA S35 (S for SOMUA and 35 from 1935, the year of introduction); today the even shorter abbreviation "S35" is most often used, in English sources usually with a hyphen: "S-35"

The hull and turret were castings with a maximum thickness of 47 mm and 40 mm respectively — the former of four sections, bolted together: two longitudinal plates formed the bottom; the superstructure was divided in a front and back section.[3] The turret was a variant of the APX 1 as used on the Char B1: the APX 1 CE (chemin élargi) with a larger 1,130 mm (44 in) as against 1,022 mm (40.2 in)) turret ring, allowing the radio operator to assist the commander in loading the gun from an ammunition stock of 118 shells (90 AP, 28 HE) and 2,250 machine gun rounds. As with the B1, the commander was expected to direct the tank while also loading, aiming, and firing the 47 mm SA 35 main gun — although at least the radio duty could be left to another crew member. Radios were planned to be part of the standard equipment of S35s. In practice the platoon commander had an ER (émetteur-récepteur) 29 set for communications with a higher command level, but a shortage of the short range ER28 sets for communication within the platoon meant that the other four tanks of the platoon were never fitted with any form of radio, although in some units all tanks had antennas: the programme to fit the sets themselves was postponed until the summer of 1940 and thus overtaken by events.

The suspension was designed by Eugène Brillié, the same man who had developed the first French tank, the Schneider CA1. He had worked with the Czech Škoda company and based his design on that of the LT35: eight road wheels paired on four bogies with leaf springs and an equally large tension wheel. The first fifty vehicles had tracks consisting of 144 track links, each link with a length of 75 mm; later vehicles had 103 links of 105 mm length.

The engine was in the rear of the hull side by side with two self-sealing fuel tanks, of 100 and 410 litres respectively, separated from the fighting compartment by a firewall bulkhead. The nominally 200 hp engine, designed by Javier-Sabin, drew fuel from the smaller tank, which was itself automatically replenished from the larger one. Inexperienced crews sometimes made the mistake of only filling the smaller tank. Engine and suspension maintenance was difficult and time-consuming, due to a poor accessibility, though this was improved in later vehicles.

The S 35 had an automatic fire extinguishing system using several tanks placed at critical spots, containing methyl bromide.

Alarmed by the rapid build-up of the Red Army, the French Army, on 24 December 1931, conceived a preliminary plan for the mechanisation of the Cavalry. This foresaw the development of several types of automitrailleuses — the official term for cavalry tanks because chars ("tanks") were by law part of the infantry arm — among which an Automitrailleuse de Combat (AMC), a lightly armoured (weighing no more than nine tons) but swift (30 km/h cruise speed) and strongly armed (47 mm gun) combat tank, capable of fighting enemy armour. The plan was affirmed by the French Supreme Command on 23 January 1932, and approved by the ministry of defence on 9 December.

Even before Plan 1931 was put on paper, Louis Renault was informed of its probable contents. In the autumn of 1931, he ordered his design team to build an AMC. The team proposed to use welded steel plates, but Renault refused as this entailed hiring expensive professional welders. Nevertheless, the team took the initiative to build the Renault VO, a fully welded prototype of a Char Rapide, that could also serve as an alternative for the AMR 33 developed at the same time. When the vehicle was finished in 1932, Renault was charmed by the proposal, but after long consideration decided against it and ordered a riveted version to be built. This quickly proved to be much too heavy and this caused a complete redesign of the project into a much smaller vehicle, the Renault YR, which was presented to the French materiel commission, the Commission de Vincennes, on 12 October 1933, still fitted with the welded turret of the Renault VO. After testing by the Section Technique de la Cavalerie the prototype was improved by installing larger fuel tanks and a stronger clutch and gearbox. On 9 March 1934, an order was made for a pre-series of twelve hulls of the AMC 34; later a choice would be made from the range of standard turrets. The first was delivered on 17 October 1935.

The AMC 34 is a small vehicle with a length of 3.98 m and a width of 2.07 m. The suspension of the prototype is identical to that of the AMR 33; the production vehicles use a type that was originally envisaged for the AMR 35: a central bogie with a vertical spring; two other wheels in front and behind with an oil-dampened horizontal spring. The engine, a 7.125 litre V-8 120 hp with a fuel tank of 220 litres rendering a top speed of 40 km/h and a range of 200 kilometers, is located on the right; the driver on the left with a hatch in front of him and an escape door behind him. The armour is 20 mm on the vertical plates; the weight — of the hull only — 9.7 metric tons.

The AMC 35 (from Automitrailleuse de Combat Renault modèle 1935), also known under a manufacturer's designation Renault ACG-1, is a French medium cavalry tank. It was developed as a result of the change of the specification that had led to the design of the AMC 34, calling for a vehicle that was not only well-armed and mobile but also well-armoured. Due to technological and financial problems production was delayed and limited. The AMC 35 was one of the few French tanks of the period featuring a two-man turret.

Renault had developed the AMC 34 according to the specifications of the Plan 1931. On 26 June 1934 these were changed: it was now demanded that the vehicle attain a maximum speed of 50 km/h (31 mph) and be immune to anti-tank guns. On 7 March 1936 a changed prototype was delivered by Renault, who requested that the vehicle would be accepted if it met the new specifications; after all the AMC 34 had already been accepted for production and this was nothing but a slightly changed variant. The French materiel commission, the Commission de Vincennes, became suspicious however by the fact that the factory designation had been changed from Renault YR to Renault ACG. When the commission inspected the prototype on 9 March it transpired that it was actually a completely new design. Accordingly, a complete test programme was ordered, which was finished on 27 November. At that date the commission judged that despite many changes the type was still unfit for service due to its mechanical unreliability. However already in the spring the Cavalry, worried by the German remilitarization of the Rhineland, had first ordered seventeen vehicles and later expanded that order to fifty. For political reasons the commission did not dare to cancel the order; it accepted the type, noting that it would be highly advisable to test types in future before ordering them. The first vehicle was received by the Cavalry on 1 November 1938.

The AMC 35 had about the same dimensions as the AMC 34, but the hull was longer at 4572 mm to install a shortened 11.08 litres V-4 180 hp version of the V-6 engine used in the Char B1. There were five road wheels. The suspension used horizontal rubber cylinders as springs. At 42 km/h the vehicle was slower than the specified speed. A three hundred litre fuel tank[1] allowed for a range of 160 kilometres. The wading capacity was sixty centimetres and it could cross a trench of two metres. The 25 mm armour plates, riveted and bolted onto the chassis, did not offer the demanded protection.

The prototype had a two-man APX2 turret, with the commander/loader on the left and the gunner on the right, fitted with a 25 mm SARF fortress gun and a 7.5 mm Reibel machine gun. As the 25 mm antitank guns were needed in the Maginot line, in the production series the 47 mm SA 35 gun was used. The roughly octagonal APX2 turret consisted of cast sections, welded, riveted and bolted together. The tank carried 120 gun rounds and 5250 machine gun rounds.

The Belgian Army had ordered 25 AMC 34 hulls with Renault on 13 September 1935 at a unit price of 360,000 French francs, together with a matching number of APX2 turrets to be delivered by Batignolles-Châtillon, for a total project budget of 18.5 million Belgian francs.[1] The hulls were indicated to be of a "second series", an improved AMC 34 — referring to the same line of development that would result in the AMC 35. Their delivery was supposed to commence in October 1935. However, that month Renault started production of the original AMC 34; it was as yet unable to manufacture the improved version. Technological, financial and social problems — in December 1936 the military division of Renault was nationalised and restructured into the new AMX-factory — ensured that for 1936 also, delivery would be delayed. As large orders had become unlikely, the project had a low priority.

On 3 June 1937 the Belgian minister of defence, General Henri Denis, demanded that the single prototype be sent to Belgium; it was transported on 4 June. After testing between 23 and 27 August showed that its climbing abilities were poor, the Belgians decided that the seven tanks intended for the Chasseurs Ardennais were unnecessary and reduced the order accordingly to eighteen. The arrival of the prototype had caused a political row however: politicians from the right feared it would antagonise Hitler and so endanger Belgian neutrality; those from the left wanted only purely defensive weapons. As deliveries failed to materialise, in December 1937 it was decided to annul the order completely, to accept a contractual fine of four million franc and to redirect the remaining budget to the production of home-made T-13 tank destroyers.

This outcome however, embarrassed the French government: it pressured Renault to accept a new arrangement. Early in 1938 it transpired that the Renault factory had in its possession the materials to build the original total of 75 tanks; out of these stocks parts sufficient for about sixty tanks had already been manufactured; assembly had started on about fifty vehicles. It was agreed on 21 April 1938 to complete 35 vehicles, ten to be delivered to Belgium including the prototype, the countervalue of its contractual fine. Belgium also was to receive five sets of reserve parts and eight armour sets. The new contract was signed on 15 June; it stipulated that the Belgian tanks would be delivered prior to 31 July. At that moment the French Cavalry no longer itself intended to use the type (but the SOMUA S35 instead) and advised that priority should be given to the Belgian order. Renault had asked permission for this on 6 May, but on 2 June the French Ministry of Defence responded that the terms of the original agreements should be followed; these entailed a split delivery of batches of ten at a time: first seven tanks for France, followed by three for Belgium.

Series production only started in November 1938 and actual delivery of the first three vehicles to Belgium was delayed till 30 March 1939, the second batch was exported in May and the final three vehicles arrived on 7 August.

In 1938 the turrets also were delivered. As there was now a surplus of fifteen, these were used on fortifications: thirteen of these on coastal defence pillboxes; another two turrets were installed on pillboxes at Remouchamps where a fortress was initially intended to be built, but due to the lack of funds only two casemates were constructed. The turrets were equipped by Belgium with a different armament: instead of the French SA 35 gun, a Belgian FRC 47 mm gun was fitted; this closely related type had a barrel that was 15 mm shorter. Also the machine gun was different: an optionally coaxial 7,65mm rechambered Hotchkiss (Maxim) 08/15 MG. The Belgian turrets were produced at Nantes as the APX2 B, which had the diascope on the left side moved to the facet behind, because the drum magazine for the 7.65mm Maxim 08/15 machine gun made it impossible to look through it in the original position. Older sources incorrectly claim that a 13.2 mm Hotchkiss machine gun was fitted. An armour plate was welded over the hole. They were rebuilt at Ghent by the SEM (Société d'Électricité et de Mécanique Van den Kerckhove & Carels) between September 1939 and February 1940.

For France also, production continued after 1 November 1938, with final assembly at AMX; in March 1939 the original order of seventeen was finished; at the beginning of the Second World War a number of 22 had been reached. Production then accelerated: three were built in September, nine in October, eight in November. For this production all remaining materials were used, apparently to fulfill the original order:[9] when in December the Belgian Army asked for the delivery of the spare parts, as it needed some tanks in working order to allow a single platoon to take part in the winter manoeuvres, Renault was unable to provide these.

The Char B1 was a specialised break-through vehicle, originally conceived as a self-propelled gun with a 75 mm howitzer in the hull; later a 47 mm gun in a turret was added, to allow it to function also as a Char de Bataille, a "battle tank" fighting enemy armour, equipping the armoured divisions of the Infantry Arm. Starting in the early twenties, its development and production were repeatedly delayed, resulting in a vehicle that was both technologically complex and expensive, and already obsolescent when real mass-production of a derived version, the Char B1 "bis", started in the late 1930s. A further up-armoured version, the Char B1 "ter", was only built in two prototypes.

The Char B1 had its origins in the concept of a Char de Bataille conceived by General Jean Baptiste Eugène Estienne in 1919, e.g. in his memorandum Mémoire sur les missions des chars blindés en campagne. It had to be a "Battle Tank" that would be able to accomplish a breakthrough of the enemy line by destroying fortifications, gun emplacements and opposing tanks. In January 1921 a commission headed by General Edmond Buat initiated a project for such a vehicle. To limit costs, it had to be built like a self-propelled gun, with the main weapon in the hull. To minimise the vehicle size this gun should be able to move only up and down, with the horizontal aiming to be provided by turning the entire vehicle. The specifications included: a maximum weight of thirteen tonnes; a maximum armour thickness of 25 millimetres; a hull as low as possible to enable the gun to fire into the vision slits of bunkers; a small machine gun turret to fend off enemy infantry attacks, at the same time serving as an observation post for the commander and a crew of at most three men. Two versions should be built, one a close support tank armed with a 75 mm howitzer, the other an anti-tank vehicle with a 47 mm gun instead.

French industry was very interested in the project. In the past, this had led to much non-constructive rivalry. Estienne, who in the war had personally witnessed the dismal effects of such a situation, was determined to avoid a repetition. He used his position as Inspector-General of the Tanks to enforce the so-called "Estienne accord" on the industrialists, ordering them to "reach a mutual understanding, free from any spirit of industrial competition". To be allowed to join, they had to agree beforehand to relinquish any patents to the Army, which would be free to combine all projects into a single type. In exchange, to the industry very large orders of no less than a thousand vehicles were promised.

On these conditions four projects were started in 1921: two by a cooperation between Renault and Schneider: the SRA and the SRB, one by Forges et Aciéries de la Marine et d'Homécourt (FAMH), more commonly known as "Saint Chamond" from its location, and the last by Forges et Chantiers de la Méditerranée (FCM), the FCM 21. Renault and Schneider would each get to produce 250 units, FAMH and FCM each 125. A fifth producer, Delaunay-Belleville, whose project (an improved Renault FT) had been rejected beforehand, would be allowed to make 83 tanks; the remaining 167 would be allotted at the discretion of the French State.

On 13 May 1924, the four prototypes were presented at the Atelier de Rueil, where they were compared, each having to drive over a twenty kilometre test course. Immediately it became evident that their technical development had been insufficient, most breaking down; the SRA even started to fall apart. Maintenance was difficult because the engines were inaccessible. All projects used a three-man crew but differed considerably in size, form and the solution chosen to laterally point the gun.

The SRA

The SRA was the heaviest vehicle at 19.5 tonnes. Its length was 5.95 metres, its height 2.26m and its width 2.49m. It had a 75 mm howitzer in the right side of the hull and a cast, 30 mm thick, turret with two machine guns. It was steered by an epicyclical transmission combined with hydraulically reinforced brake disks, which failed to provide the desired precision during tests.

Seen from the front it was very similar to the final model, but its side-on profile was more like that of the British Medium Mark D, including the snake track-system, with the drive wheel higher than the idler in front. The suspension used leaf springs. A Renault six-cylinder 180 hp engine (a bisected V12 aircraft engine) allowed for a maximum speed of 17.5 km/h; a four hundred litre fuel tank for a range of 140 kilometres.

The SRB

The SRB, also using leaf springs, was a somewhat larger vehicle, six metres long, 2.28 metres high and 2.5 metres wide. It was nevertheless lighter at 18.5 tonnes, a result of having a smaller 47 mm gun—it thus was the antitank version. Using the same engine, its speed was accordingly slightly higher at 18 km/h. More limited fuel reservoirs holding 370 litres decreased the range to 125 kilometres. It used an advanced hydraulic suspension system and the hydraulic Naeder-transmission from the Chaize company combined with a Fieux clutch and Schneider gear box. It used modified Renault FT tracks. The upper track run was much higher, creating enough room for a side door on the left.

The FAHM prototype

The FAHM prototype was 5.2 metres long, 2.4 m high and 2.43 m wide. It used a hydropneumatic suspension. Despite a less powerful Panhard engine of 120 hp it still attained a speed of 18.2 km/h. Fuel reservoirs of just 230 litres limited its range to a mere seventy kilometres. The 75 mm howitzer was placed in the middle of the hull and steered by providing each snake track with its own hydraulic Jeanny transmission. On top there was a riveted machine gun turret with 25 mm armour.

The FCM 21

The lightest prototype was the FCM 21 at 15.64 tonnes. It resembled a scaled-down Char 2C, the giant tank produced by the same company. It was very elongated with a length of 6.5 metres and width of 2.05 metres. A rather large riveted turret with a stroboscopic cupola, adopted from the Char 2C, brought its height to 2.52 metres. Like the superheavy tank it had no real spring system for the twelve small wheels per side. Separate clutches for each snake track enabled it to horizontally point the 75 mm howitzer in the middle of the hull. It used the same Panhard engine as the FAHM type and its speed was the lowest of all at 17.4 km/h. However, its 500-litre fuel tanks allowed for the best range at 175 kilometres.

In March 1925, Estienne decided to base the future production type on the SRB, as regarded the general form and mechanical parts. However, it would be fitted with the 75 mm gun, a Holt-track to be developed by FCM, which company had completed a special research programme aimed at optimising weight distribution, and the FAMH-suspension (later this would again be discarded). Estienne also had some special requirements: a track tension wheel should be fitted, adjustable from the inside, and a small gangway from the fighting room should improve the accessibility of the engine compartment. Furthermore, the front armour should be increased to 40 millimetres.

The wooden mock-up

In November 1925 Renault was given the order to build a wooden mock-up, that was finished early 1926. On 27 January 1926, it was decided to build three prototypes of what was provisionally called a Tracteur 30, a final design by engineer Alleaume of the Schneider company, cooperating with the Section Technique des Chars de Combat (STCC). The first was to be delivered by Renault, the other two by FCM and FAHM respectively.

The same year, the Direction de l'Infanterie in the Plan 1926 redefined the concept of a Char de Bataille. There would be a greater emphasis on infantry support, implying that the antitank-capacity was secondary and no armour increase was necessary. The weight was to be limited to 22 tonnes and the speed might be as low as 15 km/h. However, a radio set would have to be fitted to better direct and coordinate its actions; therefore a fourth crew-member was needed.

On 18 March 1927, the contracts for the three prototypes were signed. The hull of first Renault vehicle, made of soft boiler plate instead of armour steel to simplify changes, was finished apart from the armament in January 1929; it was delivered in March. The separately produced cast turret was delivered on 23 April. The howitzer could only be fitted in April 1930. This prototype was allotted the series number No. 101. No. 102, the production of which FAMH had shifted to Renault, was delivered soon after; in September 1930 FCM delivered No. 103, constructed by the Atelier de Mépanti at Marseille. One of the vehicles was fitted with an alternative 75 mm Schneider gun instead of the 75 mm St Chamond M 21 from FAMH.

Prototype No. 101, here in its original state with a small machine gun turret

Testing on the first prototype had already begun before the other two were delivered, or even its main armament was fitted. At 24,750 kg (24.36 long tons) the weight was more than specified but could nevertheless reach a top speed of 24 km/h (15 mph). From 6 May until August 1930 the Commission d'Experiences des Matériels de Chars carried out a further test programme on what was now officially called the Char B—the "B" not referring to Bataille but to a general classification code. The commission was largely satisfied with the vehicle, though many smaller problems were detected that had to be improved. The FCM prototype featured several alternative technologies: a Winterthur transmission, a Citroën clutch and a Sulzer diesel engine, later replaced by a Clerget diesel. All of these systems would prove to be more unreliable than the original concept and were ultimately rejected.

The three vehicles were not only used for technological, but also tactical experimentation. Together with the Char D1 pre-series, they represented the only modern tanks in France and the Army was naturally very interested in what lessons could be learned from them about future warfare, outlining the concept of a Char de Manoeuvre. Neither Char de Bataille nor Char de Manoeuvre are official type designations; they refer to the tactical concepts only. In October 1931 a small unit was formed, the Détachement d' Experimentation in which the prototypes were united from December, using the Camp de Châlons as a base to see how they could be used in winter conditions. Afterwards, they drove on their own power to the Atelier de Rueil for repairs. In September they took part in the summer manoeuvres in Champagne as a Détachement Mécanique de Combat; from 4 May 1933 No. 102 and 103 together formed a Détachement d'Engins Blindés to perform tactical experiments in the army bases of Coëtquidan and Mourmelon as part of a motorised light division, followed by comparable experiments in April 1934 at Sissonne. Technical aspects were not forgotten during these tests and it was established they could attain an average road speed of 19 km/h, cross a trench 2.4 m (7.9 ft) wide, and wade through a 105 cm (41 in) deep stream.

The prototypes were again extensively altered to meet changes in specifications. On 6 April 1934, the first order was made for seven tanks of a Char B1. The "B1" refers to the fact that there were other simultaneous projects to develop improved types: the Char B2, B3 and B B.

The Char B1 was manufactured by several firms: Renault (182), AMX (47), FCM (72), FAMH (70) and Schneider (32). Although it was the main producer, Renault had not exclusively designed the tank. Therefore, the official name was not Renault B1 as often erroneously given.[citation needed] It was a very expensive tank to build: the cost per vehicle was about 1.5 million French francs. In France at the time two schools of thought collided: the first wanted to build very powerful heavy tanks, the other a lot of cheap light tanks. Both sides managed to influence procurement policy to the end that not enough tanks were built of either category, to the exasperation of men like Colonel Charles de Gaulle, who wanted to build more of the medium Char D2 at a third of the cost of the Char B1 bis, but with the same 47 mm anti-tank gun.

The outer appearance of the Char B1 reflected the fact that development started in the twenties: like the very first tank, the British Mark I tank of World War I, it still had large tracks going around the entire hull and large armour plates protecting the suspension—and like all tanks of that decade it had no welded or cast hull armour. The similarity resulted partly from the fact that the Char B1 was a specialised offensive weapon, a break-through tank optimised for punching a hole into strong defensive entrenchments, so it was designed with good trench-crossing capabilities. The French Army thought that dislodging the enemy from a key front sector would decide a campaign, and it prided itself on being the only army in the world having a sufficient number of adequately protected heavy tanks. The exploitation phase of a battle was seen as secondary and best carried out by controlled and methodical movement to ensure superiority in numbers, so for the heavy tanks also mobility was of secondary concern. Although the Char B1 had a reasonably good speed for the time of its conception, no serious efforts were made to improve it when much faster tanks appeared.

More important than the tank's limitations in tactical mobility, however, were its limitations in strategic mobility. The low practical range implied the need to refuel very often, limiting its operational capabilities. This again implied that the armoured divisions of the Infantry, the Divisions Cuirassées, were not very effective as a mobile reserve and thus lacked strategic flexibility. They were not created to fulfill such a role in the first place, which was reflected in the small size of the artillery and infantry components of the divisions.

The origins of the Char 2C have always been shrouded in a certain mystery. In the summer of 1916, likely in July, General Léon Augustin Jean Marie Mourret, the Subsecretary of Artillery, verbally granted Forges et Chantiers de la Méditerranée (FCM), a shipyard in the south of France near Toulon, the contract for the development of a heavy tank, a char d'assaut de grand modèle. At the time, French industry was very active in lobbying for defence orders, using their connections with high-placed officials and officers to obtain commissions; development contracts could be very profitable even when not resulting in actual production, as they were fully paid for by the state. The French Army had no stated requirement for a heavy tank, and there was no official policy to procure one. Hence, the decision seemed to have been taken solely on his personal authority. The reason he later gave was that the British tanks then in development by a naval committee seemed to be better devised as regarded lay-out, ventilation and fire protection, so a shipyard might improve on existing French designs. Exact specifications, if they ever existed, have been lost. FCM then largely neglected the project, apart from reaping the financial benefits. At that time, all tank projects were highly secret, and thereby shielded from public scrutiny.

On 15 September 1916, the British introduced their Mark I (heavy) tank at the Battle of the Somme, The public mood in Britain had been growing ever darker as the overall failure of the Somme Offensive became known, tanks offered a new hope of final victory. The French public wanted to know about their own national tank projects[a] and French politicians, up til then not having been greatly involved in them and leaving the matter to the military, were also interested. This sudden attention greatly alarmed Mourret, who promptly investigated the progress that had been made at FCM and was shocked to find there was none. On 30 September, he personally took control of the project. On 12 October, knowing that the Renault company had some months earlier made several proposals to build a heavy tracked mortar which had been rejected, he begged Louis Renault to assist FCM in the development of a suitable heavy vehicle; this request Renault obliged. Even before knowing what the exact nature of the project would be, on 20 October Mourret ordered one prototype to be built by FCM.

This development coincided with a political demand by Minister of Armaments Albert Thomas to produce a tank superior to the British types. On 7 October, he had asked the British prime minister David Lloyd George to deliver some Mark Is to France but had received no answer. Concluding, correctly, that no such deliveries would materialise, on 23 January 1917 he ordered that French tanks should be developed that were faster, and more powerfully armed and armoured than any British vehicle. He specified a weight of forty tonnes, immunity against light artillery rounds and a trench-crossing capability of 3.5 metres.

Meanwhile, Renault had consulted his own team, led by Rodolphe Ernst-Metzmaier, which since May 1916 had been in the process of designing the revolutionary Renault FT light tank. This work had not, however, stopped them from considering other tank types. Renault, always expecting his employees to provide new ideas instantly, had by this attitude encouraged the team to take a proactive stance – setting a pattern that would last until 1940 – and to have various kinds of contingency studies ready for the occasion, including a feasibility study for a heavy tank. This fortunate circumstance allowed a full-size wooden mockup to be constructed in a remarkably quick time. It was visited by the Undersecretary of State for Inventions for National Defense Jules-Louis Breton on 13 January 1917, who was much impressed and developed a keen interest in the project. The design was presented to the Consultative Committee of the Assault Artillery on 16 and 17 January 1917, after the basic concept had been approved on 30 December. This proposed tank was the most advanced design of its time; it was received very favourably, also because of the enthusiastic report by Breton, and a consensus began to form that the project was most promising and a potential "war-winner". It featured a 105 mm gun in a turret and had a proposed weight of 38 tons, as well as 35 mm armour. The committee decided to have two prototypes developed, one with an electrical transmission, the other with a hydraulic transmission. In this period, both the French and British military had become aware of severe mobility and steering problems with heavy tracked vehicles; the French designs paralleled extensive British experiments with all kinds of improved tank transmissions to solve them.

In January 1917, the Ministry of Armament proposed building three weight classes of tanks: light, medium and heavy tanks,[4] the latter class corresponding to the new project. However, brigadier Jean Baptiste Eugène Estienne, commander of the new tank force, the Assault Artillery, was closely cooperating with Renault in the development of the Renault FT, and by this was well informed of the other tank project. Estienne feared that production of heavy tanks would use all available production facilities, making procurement of the - much more practical - Renault FT light tank impossible. He was not averse to the production of heavy tanks but only in a limited number and provided it did not impede the manufacture of light tanks. In November Mourret argued that all available resources should be concentrated into heavy tank production and development of the Renault FT halted. Alarmed, Estienne wrote to the Commander-in-Chief, General Joseph Joffre, on 27 November 1916 defending the light tank concept. He admitted that "colossal landships" might in certain circumstances have their uses, but claimed that while it was as yet unproven that a workable heavy type could be developed, let alone produced in sufficient numbers by French industry, it would be folly not to give priority to light tanks that could be constructed without delay. He insisted that Joffre use all his influence to bring about the cancellation of the heavy tank project.

Joffre answered that Estienne was no doubt correct in his tactical and organisational analysis, but that political backing of the heavy tank was simply too strong. The Minister of Armament, Albert Thomas, had committed himself openly to Mourret's cause and did not dare to retract support now. Joffre advised Estienne that he would make sure that the Renault FT would not be cancelled, and since heavy tank development would take such a long time it would not - for the immediate future - get in the way of light tank production. There would surely be no harm in allowing some prototypes to be built.

The Consultative Committee of the Assault Artillery (Comité Consultatif de l'Artillerie d'Assaut , CCAS) had been created on 13 December 1916 and met for the first time on 17 December. During this first session it was reported that Renault and FCM were cooperating on a heavy tank project of thirty tonnes. Estienne on this occasion stressed that production should be "orientated towards small types and very large types". During the next meeting on 30 December, Estienne was surprised to discover that for no clear reasons a 105 mm gun was planned; he himself preferred a 75 mm gun. Estienne was absent on the crucial meeting of 17 January, but by letter informed the committee that he found the project satisfactory and agreed with the quick construction of two prototypes; he stated his preference for a 75 mm over a 105 mm gun.

In December Joffre was replaced as supreme commander by Robert Nivelle. In late January Nivelle learned of the heavy tank project from Estienne. He was much more alarmed than Joffre had been. On 29 January he wrote a letter to Thomas, making clear that under no circumstances could the project be allowed to impede production of the Schneider CA. Thomas answered on 5 February that there was no danger of this; anyway he had just happened to affirm on 1 February the policy of General Mourret, who had already ordered the simultaneous development of three prototypes: the lightened 30-tonne "A" version, 6.92 metres long,[b] with a 75 mm gun, to fulfil the original order of 20 October; the 45-tonne "B" version with a longer hull (7.39[c] metres), armed with a 75 mm gun and two machine guns, and the 62-ton "C" version 9.31 meters long[d] with a 75 mm gun. Nivelle's misgivings were reinforced by inquiries from a parliamentary financial commission led by Pierre Renaudel. A plan by Breton to immediately order fifty vehicles more or less identical to the mock-up was therefore rejected. The 1 February order of two additional prototypes was confirmed by the CCAS on 7 February. Eventually the "FCM 1A" would be developed with a 105 mm gun and the "FCM 1B" would use a petrol-mechanical transmission.

At first, progress with the FCM 1A prototype was satisfactory. Moritz was assured by Renault in January 1917 that the desired 200 CV (150 kW) engines were reliable and would pose no danger to the project. Moritz predicted that the first prototype would be ready by 1 May 1917. On 10 April 1917 he still assumed that the first trials could have begun within five weeks. On 16 April the Nivelle offensive began, although it had tactical successes it failed to deal a strategic defeat on German forces and the first use of French tanks led to heavy losses (76 of the 128 combat tanks engaged were lost); in reaction Thomas ordered all tank production and projects to be ended. This led to an emergency alliance between Estienne and Mourret to bring about a reversal of this decision. While Thomas was visiting Russia, Mourret surreptitiously ordered a restart of the tank projects. On his return an enraged Thomas caused Mourret to be fired, removing Estienne's greatest rival. Meanwhile, there were unexplained delays in the delivery of the engines and the gearbox by Renault. On 5 June, FCM could only take note that the promised pieces had not arrived yet. On 24 June the ministry of armament complained about the situation. On 13 August Breton was told by Renault personally that it would take at least another three weeks. A possible explanation of the delays might be a decision by Renault to give priority to other projects. During a meeting of the CCAS on 18 October, Moritz at last announced that trials could begin on 20 November. In that meeting Estienne was critical of heavy tanks: "the infantry has as much need of large tanks, as it needs 400 mm cannon; it has need of small tanks, as much as it needs 37 mm and machine-guns".