The Automitrailleuse de Reconnaissance Renault Modèle 35 Type ZT (AMR 35 or Renault ZT) was a French light tank developed during the Interbellum and used in the Second World War. It was not intended to reconnoitre and report as its name suggests but was a light armoured combat vehicle, mostly without a radio and used as a support tank for the mechanised infantry.
The AMR 35 originated from a project in 1933 to improve the earlier AMR 33 by moving the engine from the front to the back. In 1934, a stronger suspension was fitted and the type was chosen to replace the AMR 33 on the production lines that year. Three orders were made by the French Cavalry, totalling two hundred vehicles in five versions, including two machine-gun tanks, two tank destroyer types and a command tank. Later, ten were ordered of a radio communication variant, the Renault YS, and over forty were built of a tropical version, the ZT 4.
The production would be much delayed by financial and technical problems, deliveries only starting in 1936. The AMR 35 proved to be an unreliable vehicle. It was one of the fastest tanks of its day, but its very speed overstressed its mechanical parts. In 1937, it was decided not to make any further orders but organisational difficulties slowed final deliveries of some versions until well into 1940; even by the time of the Fall of France in June 1940 the ZT 4 order had not yet been finished.
During the Battle of France, the AMR 35s were part of armoured and motorised divisions, the vast majority being lost during the first weeks of the fighting. During the remainder of the Second World War, Germany made use of some captured vehicles.
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 been lengthened and refitted with a much more powerful Nerva Stella 28 CV engine in September 1933,Touzin (1976), p. 67 which now was placed at the back, instead of the front, of the vehicle. This was to reduce the effect of engine noise as well 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, 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.Touzin (1976), p. 68 A subsequent order of 92 for the second version 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 were to 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 were to 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 a hundred vehicles.Touzin (1979), p. 53
At this time, however, it became clear that the AMR 33 suspension system, which originally had been intended to be used on the AMR 35, 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 had two bogies and five road wheels, like the R 35. This Renault ZB was rejected; however, in March 1936, twelve were ordered by China and four a few months later by the Yunnan province administration. The latter were delivered in October 1938, the former only in 1940.Ness (2002), p. 217 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 on a third prototype, newly built in September 1934 from boiler plate; its idler wheel was still of the AMR 33 suspension type and its turret was that of the second prototype.
Description The production vehicles would differ slightly from the third prototype:Touzin (1976), p. 69 they had more riveted, instead of bolted, plates and used the Renault 447 engine.
The AMR 35 was somewhat larger than the AMR 33, being 3.84 metres long, 1.76 metres wide and 1.88 metres tall. It weighed, fully loaded, 6.5 metric tonnes (six tonnes unloaded). The vertical armour plates had a thickness of thirteen millimetres, the sloped plates being nine millimetres thick and the top and bottom plates six millimetres.
Its general configuration was changed in that the engine was moved to the back. Originally, it had been intended to give the driver a more central position to improve his view to the right but eventually he remained at the left side of the hull, the right side being occupied by a large ventilation grill. The turret, where the second crew member, the commander/gunner, was located, was also placed left of centre. Two types of turret were used: the Modèle réglementaire AVIS-1 fitted with the 7.5 mm Modèle 1931 Type C machine-gun and an ammunition stock of 2,250 rounds and the AVIS-2 with a 13.2 mm machine-gun. The 7.5 mm version also had a reserve machine-gun that can be placed on a small mount on top of the turret for AA use. If a radio was present, it was the ER 29, operated by the commander.
The suspension used four much more robust road wheels. The two in the middle were paired into a central bogie, sprung by a horizontal rubber cylinder block, that again consisted of five smaller rubber cylinders separated by steel discs. These cylinders also served as shock dampers, avoiding the problems caused by the oil dampers used with the AMR 33. The wheels in the front and back were independently sprung, again by a rubber cylinder block, but now consisted of four smaller cylinders. The sprocket was in the front. The track was twenty-two centimetres wide and was supported by four top rollers. The wading capability was sixty centimetres, the trench crossing-capability 1.7 metres and a vertical obstacle of fifty centimetres or slope of 50% could be climbed.Touzin (1979), p. 55
The Renault 447 22 CV four-cylinder 5881 cc petrol engine rendered, according to the official French Army manual, a maximum speed of 55 km/h, making it the fastest French tank of its day. Renault brochures claimed the higher speed of 60 km/h and many sources mention the latter number. It had a peak output of 82 hp at 2200 r/m. The average road speed was 40 km/h. The brakes were of the single dry plate type and a Cleveland differential was used. There were four forward gears and one in reverse. There was a Zénith carburettor and a Scintilla Vertex magneto, making it possible to start electrically even at temperatures below zero. A fuel tank of 130 litres gave it a range of two hundred kilometres.
Production The original order envisaged a first delivery of ten vehicles in December 1934 and a completion in March 1935. This last date was soon postponed to August 1935, but that month production had hardly started yet due to great financial problems with Renault. In June 1935, Renault even refused a second order of fifty, fearing the contractual fines the inevitable delays would cause. However, on 20 April 1936, he accepted an additional order for thirty vehicles, to be delivered before 15 December 1936. Of these, fifteen would be of the 7.5 mm machine-gun version, five of the ADF 1 and five each of two tank destroyer types, the ZT 2 and ZT 3. On 9 October 1936, a third and final contract was signed for seventy vehicles: sixty of the 7.5 mm machine-gun version, half of these without a radio set; and five each of the ZT 2 and ZT 3, with a final delivery before 7 August 1937.
The onset of production was also slowed by coordination problems with the subcontractors: Schneider would produce the armour plates and construct empty hulls; Batignolles-Châtillon would make the AVIS-2 turrets. Final assembly was by Renault.
In March 1935, Schneider delivered the first empty hull. On 20 May, this hull was finished and sent to Satory for tests. When these had been successfully completed on 24 June, another vehicle, the third of the production series, was sent to the STC (Section Technique de Cavalerie) for further testing. The Satory vehicle was fitted with a turret and again tested between 3 and 7 August without serious problems. On 9 August, however, the STC vehicle failed to climb a 50% slope, even though the other vehicle had done so effortlessly. This would be the beginning of a series of severe delays. The Army demanded that the gear ratio be changed and on 2 September refused to accept the first batch of twelve vehicles. On 19 October, the first modified vehicle was finished and the first eleven vehicles were only accepted in January 1936 and the first AMR 35 taken into service on 22 April 1936.
Meanwhile, the Citroën factory had tried to take over the order by developing the AMR Citroën P 103, which had a very novel hydraulic suspension, but this project was rejected.
By 22 February 1936, thirty AMR 35s had been produced; twenty more were being worked on. By the end of June 1936, production numbers had reached 76 tanks, 41 of which had been delivered. At that moment, however, a very serious reliability problem emerged that was to slow down production considerably. Many mechanical parts proved to be too weak; especially the Cleveland differentials, which were not capable of taking the stress loads caused by the tank's high speed. Much of the factory capacity in 1937 was used to rebuild and modify the entire first production batch of 92. On 8 April 1937, Renault was forced to submit two modified vehicles — one of each of the two main versions — for acceptance as "prototypes". This upgrading project did not result in a very reliable vehicle though: in October, the Ministry of War was amazed to find out that out of 43 vehicles, of which the differential had already been replaced five times, six were again in need of a new one.