The SOMUA S35 was a French cavalry tank of the Second World War. Built from 1936 until 1940 to equip the armoured divisions of the Cavalry, it was for its time a relatively agile medium-weight tank, superior in armour and armament to its French and foreign competitors, such as the contemporary versions of the German Panzer III medium tank. It was constructed from well-sloped, mainly cast, armour sections, that however made it expensive to produce and time-consuming to maintain.
During the German invasion of May 1940, the SOMUA S35 proved itself to be a tactically effective type, but this was negated by the French command's strategic mistakes in deploying their Cavalry armoured divisions. After the defeat of France in June 1940, limiting production to a total of about 440, captured SOMUA S35s were used by the Axis powers, some of them on the Eastern Front. A derived type, the SOMUA S40, with an improved suspension, lowered hull cast and welded turret armour, had been planned to replace the original version on the production lines in July 1940. Agreements to produce this improved type for the benefit of Vichy France, Germany, and Japan, ultimately did not lead to any manufacture.
Development The design of the SOMUA S35 comes from the changed specifications of 26 June 1934 for an Automitrailleuse de Combat (AMC) issued for cavalry use. These called for a much heavier design than had been originally specified in 1931. The new type had to be immune to contemporary anti-tank guns. By 17 May the Army had already contacted a subsidiary of Schneider et Cie — the Société d'Outillage Mécanique et d'Usinage d'Artillerie (SOMUA) based at Saint-Ouen — to build a prototype. The company accepted this proposal on 16 July and construction began on 12 October 1934. The prototype, with the name AC3, was ready on 14 April 1935. It was tested from 4 July until 2 August 1935. Then a pre-series of four was produced of an improved type, the AC4, to be tested until 27 January 1938. These first vehicles had the standard APX1 turret, fitted with the short 47 mm SA 34 gun. On 25 March 1936, the AC4 design was accepted as the standard medium tank of the French Cavalry with the official name Automitrailleuse de Combat modèle 1935 S (AMC 1935 S), when a first order for fifty was made. The tank was then more commonly known as SOMUA S35 (S for SOMUA and 35 from 1935, the year of introduction); today the even shorter abbreviation "S35" is most often used, in English sources usually with a hyphen: "S-35".
The mass-production vehicles would have the longer SA 35 gun. Originally, a total production of six hundred was planned to provide each of the three Cavalry armoured divisions with two hundred tanks. Later, budgetary restraints led to a more gradual and limited procurement. In 1936 a second order was made of fifty, followed by a hundred in 1937, and two orders of 125 each in 1938, resulting in total prewar orders of 450 units.François Vauvillier, 2013, "Le Somua S 35, Genèse et Production", Histoire de Guerre, Blindés & Matériel, N°105, p. 83-95
Description The hull and turret were castings with a maximum thickness of 47 mm and 40 mm respectively — the former of four sections, bolted together: two longitudinal plates formed the bottom; the superstructure was divided in a front and back section.Danjou (2004), p. 7 The turret was a variant of the APX 1 as used on the Char B1: the APX 1 CE (chemin élargi) with a larger instead of diameter turret ring, allowing the radio operator to assist the commander in loading the gun. The ammunition carried was 118 shells (90 AP, 28 HE) and 2,250 rounds for the machine gun. As with the B1, the commander was expected to direct the tank while also loading, aiming, and firing the 47 mm SA 35 main gun — although at least the radio duty could be left to another crew member. Radios were planned to be part of the standard equipment of S35s. In practice the platoon commander had an ER (émetteur-récepteur) 29 set for communications with a higher command level, but a shortage of the short range ER28 sets for communication within the platoon meant that the other four tanks of the platoon were never fitted with any form of radio, although in some units all tanks had antennas: the programme to fit the sets themselves was postponed until the summer of 1940 and thus overtaken by events.Danjou (2004), p. 10
The suspension was designed by Eugène Brillié, the same man who had developed the first French tank, the Schneider CA1. He had worked with the Czech Škoda company and based his design on that of the LT35: eight road wheels paired on four bogies with leaf springs and an equally large tension wheel. The first fifty vehicles had tracks consisting of 144 track links, each link with a length of 75 mm; later vehicles had 103 links of 105 mm length.
The engine was in the rear of the hull side by side with two self-sealing fuel tanks, of 100 and 410 litres respectively, separated from the fighting compartment by a firewall bulkhead. The nominally 200 hp engine, designed by Javier-Sabin, drew fuel from the smaller tank, which was itself automatically replenished from the larger one. Inexperienced crews sometimes made the mistake of only filling the smaller tank.Danjou (2004), p. 9 Engine and suspension maintenance was difficult and time-consuming, due to a poor accessibility, though this was improved in later vehicles.
The S 35 had an automatic fire extinguishing system using several tanks placed at critical spots, containing methyl bromide.
Tactical function
Like the British and the Soviets, the French believed in a strict division of labour between cavalry tanks and infantry tanks; by law, tanks (chars) were limited to the Infantry and the Cavalry had to name its tanks automitrailleuses.
The French Army preferred to fight a defensive battle, and was convinced it would be victorious in such an engagement, but understood that the strategic situation might impose the necessity of waging offensive warfare; during the Second World War for 1941 large offensives against Germany were planned, based on an expected French and British material superiority.François Vauvillier, 2006, "Nos Chars en 1940 : Pourquoi, Combien", Histoire de Guerre, Blindés & Matériel, N°74, p. 40-41 Each of the two phases of an offensive – the breakthrough by the Infantry and the exploitation of it by the Cavalry – called for its own specialised vehicle, with the AMC designed to fight enemy armour. The SOMUA S35 was optimised to fulfill the latter role; it had good speed, an adequate range, a gun powerful enough to easily destroy its two probable opponents - the Soviet BT-7 and the German Panzer III - and armour thick enough to be practically immune to the fire of both at normal battle ranges; the armour of any German tank in May 1940 could be penetrated by the S35's 47 mm gun up to a range of .Danjou (2004), p. 8 So it could carry out deep strategic penetrations and destroy enemy armour reserves trying to prevent them, possessing a good anti-tank capacity. The S35 is sometimes described as the best medium tank of the 1930s.White, Brian Terrence, 1983, Tanks and other Armoured Fighting Vehicles of World War II, Peerage Books London, p.92
The French Cavalry, however, judged their main tank to be imperfect in many respects. The one-man turret, though it is today typically mentioned as its single most important drawback, was not seen as a major flaw. A commander was supposed to acquire such a degree of dexterity that his workload did not negate the lack of need to coordinate the actions of three men in a larger turret crew or the advantage of a quicker reaction because of a superior rotation speed. In combat, the tank commander threatened to be overwhelmed with duties, since in addition to his command functions within the tank he was also responsible for aiming and firing the 47mm turret gun and co-axial 7.5mm machine gun. At first, a two-man-turret was required, but when it transpired that this would reduce the armour protection, it was abandoned in favour of thicker steel casts. The CE turret variant mitigated the workload of the commander as it constituted a "one and a half man" turret.
The Cavalry acknowledged three flaws at the tactical, the operational and the strategic levels. The main tactical flaw was the hatchless cupola, forcing the commander to fight buttoned-up. This had been caused by the need to adopt the APX-1 turret, purely for budgetary reasons.François Vauvillier, 2007, "Notre Cavalerie Mécanique à son Apogée le 10 Mai 1940", Histoire de Guerre, Blindés & Matériel, N° 75, p.47 The B1 bis's APX4 turret faced similar criticism from the Infantry.
The operational flaw was its poor mechanical reliability. The suspension units were too weak and too complicated, demanding enormous maintenance efforts, especially since the cast armour modules did not allow an easy access to the suspension and engine. Repairing broken tracks in the field was well-nigh impossible. This had been caused by the fact that there was no central institution regulating French tank development. The Army branches issued very vague specifications, leaving it to private enterprise to come up with precise proposals. The French machine tool national stock was relatively outdated and tank designs reflected the limited existing production facilities. To introduce a Christie suspension — the obvious solution — demanded a thorough industrial modernisation and the raising of quality standards. It was not envisaged until September 1938, when cooperation started with the United Kingdom in order to adopt the cruiser tank suspension for French tank design, and then was limited to the development of a totally new cavalry tank, the AMX 40, without planning to introduce this feature into the S35/S40 production run.Stéphane Ferrard, 2011, "Le Char de Cavalerie AMX 40", Histoire de Guerre, Blindés & Matériel, N°95, p. 78-86
The strategic flaw was the high unit price of the tank, 982,000 French Francs, and the limited number of large cast sections that could be produced.Zaloga, 2014, p. 15 The tank had to be supplemented by a cheaper type and the only one available had been the Hotchkiss H35, much inferior in armour, armament and speed, even after it had been improved to the "H39" variant. The Cavalry had a very low opinion of the fighting value of this light tank. It decided to keep a large number of S35s in the core of their armoured divisions and rejected the easy method of raising more of them by dividing the S35s among the Cavalry Light Divisions — in contrast to the Germans who distributed the also low number of Panzer IIIs partly to their Leichte Kavalleriedivisionen — a key decision changing the Mechanised Light Divisions into true armoured divisions. It also decided against the continued mass production of even lighter vehicles like the AMR 35 and AMC 35. This again implied that the Germans would in May 1940 have a large superiority in strategically mobile large armoured units, of ten to three, because the four French armoured divisions of the Infantry did not possess sufficient organic artillery and infantry to operate effectively in an independent role. France intended to raise many more armoured divisions for use in a decisive offensive in 1941. As the French production capacity for cast armour sections was insufficient, at the time of the defeat negotiations were ongoing to employ American producers, and during the crisis caused by the German attacks in June it was even proposed to let US firms build two thousand vehicles.Danjou (2004), p. 13
Production and operational history