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. 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.
Pierre-Yves Gilliéron, Quentin Ladetto