AMR 35 - Development

Development

With his AMR 33 not yet being delivered to the French army — this would happen in June 1934 — Louis Renault used two of the five AMR 33 prototypes to improve the type. In the middle of February 1934 he sent the first, N° 79759, to the testing commission, after it had from September 1933 been lengthened and refitted with a much more powerful Nerva Stella 28 CV engine, which now was placed in the back, instead of the front, of the vehicle, both to reduce the effect of engine noise as to attain a better weight distribution, two problems that had become apparent in 1933 when the prototypes had been used for manoeuvres. The exhaust pipe was placed at the back and the ventilator moved from the right to the left side. Renault was hesitant to introduce such expensive improvements in the production run; but in February 1934 the head of the French Cavalry, General Flavigny, insisted on these changes being made.

During testing the maximum speed was shown to be an impressive 72 km/h. Weight was just 4.68 metric tonnes (to which a 0.25 tonne simulation weight was added), the average road speed 40.5 km/h. However, some cavalry officers pointed out that the Renault Nerva Stella was a sports car and its engine rather delicate and thus unsuited to the rigours of military service. They proposed to use a more robust Renault city bus engine instead. In March the second prototype prototype, N° 79760, was also lengthened twenty centimetres and fitted with a Renault 432 22 CV four-cylinder bus engine. This vehicle, with a weight of 5.03 tonnes and a simulation weight of 0.75 tonnes, was tested between 3 and 11 April at Vincennes and attained a maximum speed of 63.794 km/h and an average speed of 35.35 km/h. A subsequent order of 92 for the second vehicle with its more reliable engine was made on 3 July 1934. This type, replacing the AMR 33 in the production run, was to have the name AMR 35. Of these, twelve should be of a platoon command type, fitted with the AVIS-1 turret with a 7,5 mm machine gun and equipped with an ER1 radio set. The remaining eighty vehicles would have a larger AVIS-2 turret with a 13.2 mm machine gun; 31 of the latter were also intended to be equipped with ER1 radio sets, though in 1937 it was decided to abandon this plan. Also eight radio command tanks were to be produced, which eventually would be called AMR 35 ADF 1, bringing the order to a total of hundred vehicles.

At this time however it became clear that the AMR 33 suspension system, that originally had been intended to be used on the AMR 35 also, was very unreliable: the suspension units were simply too weak to withstand the forces caused by driving cross-country. A complete redesign of the suspension was ordered, also to be used for the new Renault R35. Three types were considered and tested on AMR 33 prototype N° 79758; the first had the idler resting on the ground; the second two bogies and five road wheels, like the R 35. This Renault ZB was rejected, but in March 1936 twelve were ordered by China and four a few months later by the Yunan province administration. The latter were delivered in October 1938, the former only in 1940. The third suspension type had only one bogie per side and was accepted. The Renault factory designation of the vehicle with the relocated engine and new suspension was Renault ZT; it merely indicates the chronological order of Renault's military prototypes and has no further meaning.

The new suspension was first tested on a third prototype, in September 1934 newly built from boiler plate; its idler wheel was still of the AMR 33 suspension type and its turret was that of the second prototype.