Status Report: How Renault R35 started
On 2.8.1933, the French army issued the requirements for a new light tank, that was to replace the - now hopelessly obsolete - FT-17 tanks. According to these demands, the vehicle was to have following specifications:
- combat weight: 6 tons
- armor no less than 30mm
- two crewmembers
- armament consisting of two machineguns or one 37mm gun
- average speed of no less than 8-10 km/h
At that time, for an infantry support tank the specifications were more than sufficient - another matter however was that this was basically just something like Panzer I or FT-17, only with more armor. On the other hand, the British at that time were building stuff like the Vickers Light Tank Mk.II and Mk.III, which were hardly any better.
In total 14 companies participated in the competition, but by 1934 the number was reduced to 7. In the end, prototypes were built of only 5 company proposals, 3 of which were later mass-produced: Renault R35, Hotchkiss H35 and FCM 36. The first company to respond to the demands was Renault. As the basis for the new vehicle, Renault VM (future AMR 33) was chosen and the new vehicle (designated Renault ZM) was derived from it, using the same suspension with horizontal springs (only paired). In order to reduce the ground pressure by increasing the track surface, fifth roadwheel was added while the idler was put as low as possible. The tracks were the same as on Renault VM as well, only wider.
The hull however was made from scratch, its parts were completely cast and riveted together - this became the standard later on for all the French light and medium tanks. The armor was based on the demands: it was 30mm thick. The hull was also wider, even though the driver was not exactly comfortable. The tank was powered by a 82hp engine.
The turret was cast as well and - again, based on the requirements - it was armed by a pair of MAC Mle.1931 machineguns. The turret armor was 40mm thick all around, but this thick armor was the only thing the Renault ZM turret could boast with. The turret was cramped even for one person, who couldn't see anything from it to boot - there were no optics apart from the gunner sights. The only thing the commander could do was to open the hatch and lean outside, risking a bullet to the head.
The Renault ZM prototype was finished by the end of 1934 and in December, it was transferred to undergo trials. However, in the meanwhile, on 22.5.1934 the military changed the requirements for the light tank - according to the new version, the vehicle was to be resistant to 25mm AT gun fire, which meant increasing the armor to 40mm. That also meant that the Renault ZM armor was no longer sufficient. On the other hand, the military requirements were not very realistic and as usual the army wanted more than was possible, preferably yesterday. It was not possible to fit all that into 6 tons, the weight increased to 7150kg for starters and if the vehicle was to have all the armor 40mm thick and a 37mm gun (which was also a part of the new requirements), the weight would reach 10 ton with considerable reduction of tank mobility. There was however no other way, the currently tested Renault ZM configuration wouldn't make it to the French army anyway.
As one of the last steps, on 18.4.1934, the APX design bureau (future ARL) developed the future turret for the vehicle with 37mm SA18 gun. The turret (designated APX R) was installed on the Renault ZM in early 1935 and went through series of successful trials, after which it was accepted as a standard turret.