The French plan of 1926, calling for the creation of a Light Infantry Support Tank, led to the development of the existing Renault NC1 prototype into the Char D1.

This implied that in the early twenties France had the strongest and most modern armoured force in the world, but this very fact led to a state of complacency.

The remaining Renault FT vehicles, though having shown themselves to be very effective in trench warfare, were not well adapted in their present state of technological development to peacetime conditions.

The main problem was their low top speed, which necessitated special tank transporters whenever the vehicles had to be moved outside their base area and made them fundamentally unsuited to patrolling duty in the colonies.

The first modifications were of the Renault FT Kégresse-type, which featured the suspension of the Kégresse half-track, fitted with a special rubber steel-reinforced track.

In 1929 he obtained an order of ten vehicles for Japan, there called the Renault Otsu-Gata ("Type B"); and 24 more were according to some sources delivered to Poland, fitted with 25 mm side armour, bringing the weight from 7.5 to 9.5 metric tons.

Also a new suspension system was tested incorporating the special chenille légère ("light track") designed by Colonel Balland, which was optimised for high speeds.

The Army made a choice in March 1929 for the second prototype, the NC3 gun tank, and ordered a pre-series of ten vehicles in December 1929.

To prevent that each time the gun was loaded, the breech had to be lowered into the fighting compartment or otherwise the round could not be shoved in, the main armament had been placed in a very forward position.

On 13 April the Ministry answered that Renault seemed to have forgotten to indicate to which type exactly his request pertained, though this matter was quite relevant "given the secret character presented by certain of your matériel".

In that case, the ministry replied on 21 April, it regrettably had to withhold its permission: no types more modern than the Renault FT or NC could be destined for licence production.

[2] The Char D1's Renault FT ancestry can still be seen from the sloping engine deck and the profile of the side armour plates; it is also still a rather narrow vehicle, only 2.16 metre wide.

For its time the Char D1 was relatively well armoured; as a result the hull alone weighs 11 metric tons, rather heavier than a typical light tank of the period.

He can operate, via a steel cable, a fixed 7.5 mm Reibel machine gun low in the nose, that is almost completely hidden behind the armour.

The hatch in the back of the main armour could be opened through the square hole of the extension, providing more room for the commander, who, when operating the gun, would still enjoy some protection against small arms fire, without the weight penalty of a larger turret.

This was partly caused by the large protruding diascopes at the sides, but also a result of forcing the commander to operate in three height levels: he had to stretch himself to observe his surroundings via the cupola, had a forward observation hatch that he could look through while standing in a normal position and had to crouch to operate the 47 mm SA34 gun to the right of him and the coaxial 7.5 mm machine gun to the left.

Needless to say, the army was very critical of this general arrangement, but it could not be rejected as deliveries were already greatly delayed: the first replacement turrets were fitted only in early 1936.

It now should function as the Char de Bataille, with the main task of fighting enemy armour, as was shown by the choice for a 47 mm gun and the presence of radio sets.

As the threat of war steadily increased, first through Soviet military build-up and then because of Germany's rearmament, the modern equipment was supposed to show to foreign powers that France was still a force to be reckoned with.

In March 1934, when 110 vehicles had been delivered, it was reported that seventeen of these were already worn out and had to return to the factory for a complete rebuild; of the remaining 93, 62 were non-operational because of major defects.

The burn-through of brakes and transmissions was common; the armour plates were bent out of shape because the chassis was not stiff enough, their rivets regularly snapping.

In 1935 a large maintenance programme was started to improve the Char D1's mechanical reliability; but when in March 1936 the elite units had to hurry to the German border in reaction to the Rhineland Crisis, it became painfully obvious how poor their readiness still was.

The new ST2 turret only worsened the situation: the glass of the diascopes was discovered to shatter by mere driving; there was no AP-shot available, except for about twenty tanks equipped with the naval 47 mm gun, fitted because the regular SA34 was in short supply; the munition racks hadn't yet been changed to hold the larger rounds.

Even though some modifications were implemented, such as a changed antenna base that did not obstruct turret rotation, early 1937, when newer types were available, all Char D1s in mainland France were phased out, with the exception of the NC31s.

Remarkably, in view of the fact that even a reserve of this size was insufficient given the poor reliability, a Cavalry unit, 5e Chasseurs, was allowed to appropriate twenty tanks for its own use, without any proper authorisation for this.

To cover the retreat, 67 BCC on 12 June reinforced the 6th Colonial Infantry Division [fr]'s defence of the village of Souain, a position blocking 8.

When the Italian armistice control commission visited, these tanks were successfully hidden behind the stable for mad[clarification needed] horses.

To ensure adequate coordination between tanks and artillery during modern manoeuvre warfare, good radio connections are essential.

Plan 1934 of the Infantry, outlining future tank design, therefore foresaw the production of a special radio tank, the Char Observatoire that was not, as its name might suggest, itself an artillery observation vehicle, but had to transmit information, gathered by the real observation vehicles of the Renault YS type, to the artillery units.

After the war it has long been assumed that the surviving pictures of this vehicle showed a presumed command tank, the Char Colonel.