The Char G1 was a French replacement project for the Char D2 medium tank. Several prototypes from different companies were developed from 1936 onwards, but not a single one had been fully completed at the time of the Fall of France in 1940. The projects represented some of the most advanced French tank design of the period and finally envisaged a type that would have been roughly equal in armament and mobility to later World War II standard tanks of other nations, such as the Soviet T-34 and the American M4 Sherman, but possessing several novel features, such as gun stabilisation, a semi-automatic loader and an optical rangefinder.

By 1935 the French Infantry had not yet developed a satisfactory medium tank. Whereas a reasonably effective heavy breakthrough tank was available, the Char B1, and several light infantry support tanks were on the brink of being taken into production – the Renault R35, Hotchkiss H35 and the FCM 36 – a good medium tank had still to be designed, as the Char D1 was a manifest failure and the Char D2 only a slight improvement over its ancestor. Such a medium tank was needed in a minimal number of 250 to serve in the planned organic tank battalion of the five Mechanised Infantry Divisions, the main Infantry force capable of executing strategic offensive or defensive movements. A good medium tank was already under development by the French Cavalry, the SOMUA S35, but the Infantry rejected this type, both because of technological reasons – its climbing capacity was limited – and because the Infantry wanted to assert its dominance over the Cavalry in the field of tank design.

On 18 December 1935 the first specifications were issued by the Infantry for a Char Moyen d'Infanterie de 20 tonnes ("twenty tonne medium infantry tank"). They called for a tank with a road speed of 50 km/h, an off-road speed of 20 km/h, a range of 400 kilometres, a trench crossing capacity of two metres, a wading capacity of 120 centimetres, a climbing capacity of eighty centimetres and 45° slope, a 47 mm gun and 7.5 mm machine-gun, an armour thickness of 40 mm, a gas-proof hull and the possession of a radio set. The weight limit of twenty metric tonnes was chosen because of railroad, bridge carrying and pontoon constraints. Overall these features were close to those of the SOMUA S35.

In May 1936, the Conseil Consultatif de l'Armement accordingly decided that French industry would be invited to initiate studies on the design of a tank having sufficient protection and armament to fight other armour, but light enough (twenty tons or less) to be both cheap and mobile. However, during this period, it began to be increasingly realised that the Char B1 was overly complex and expensive and two tonnes heavier than necessary because of using riveted armour plate instead of cast or welded armour. A twenty-tonne tank would be lighter, swifter, cheaper, more easily produced and require less training. It was therefore also decided that the new twenty-tonne tank should be able to serve as a future battle tank, eventually replacing the older heavy tank.

In October, a special commission revealed to the French industry the changed specifications for the "twenty tonne tank": a maximum speed of at least 40 km/h; a range of 200 km; a protection level equal to that of the Char B1 bis (i.e. 60 mm all around); a trench crossing capacity of 250 cm; a complete protection against gas attack; the dimensions should not impede rail transport and the armament should consist of a high-velocity gun capable of destroying all expected enemy medium tanks, combined with two machine guns.

The specifications implied that the vehicle would have been the most potent and modern French tank yet developed. It also entailed that its introduction would not take place in the near future, as it was simply too advanced. This way it was avoided that a decision would have to be reached about the future course the Infantry tank weapon should take. At the time, there were officers, like Charles de Gaulle, who proposed that the Infantry raise armoured divisions that were similar in organisation to the Divisions Légères Mécaniques of the French Cavalry or the German Panzerdivisionen, i.e. balanced forces with much organic mechanised infantry and motorised artillery, that would be flexible enough to fulfill all possible tactical roles. Other officers however considered it redundant to imitate the cavalry and thought the infantry should stick to its proper task: the break-through only. Some of them wanted that the money to be spent on armoured divisions to instead go to the production of a sufficient number of light infantry tanks to give each division its own organic battalion, as the best way to ensure an effective execution of combined arms tactics. Some wanted only heavy tanks to be built. The Char G, mobile, but heavily armoured enough to function as a break-through tank, only made sense if German-style armoured divisions would be created and a definite decision about its production could only be made when the role-of-the-Infantry debate had produced a clear winner.

Despite this uncertainty about its future, the project generated enormous interest among French industrialists, as it had a real potential to become France's main AFV building programme, leading to large state investments that the industry badly needed during the period of the Great Depression. In late 1936 and early 1937, seven companies submitted plans: Baudet-Donon-Roussel; FCM; Fouga; Lorraine de Dietrich; Renault; SEAM and SOMUA. One company, Batignolles, announced a plan, but did not actually submit one.

The commission issued its report on each proposal on 20 February 1937. For two of these, the report forms the main source of information because they would be discontinued within a year: the SOMUA design resembled a cross between the SOMUA S40 and the Sau 40 self-propelled gun; it was basically a SOMUA S35 with better climbing capacity. Of the FCM design no details are known but it seemed to have had the general outline of the FCM 36, though with its dimensions about 20% larger and equipped with a FCM F4 fortification turret.