Back to the 6 ton class
Improving armour technologies were the impulse that drove French tank development forward. As a rule, armoured plates at the time were connected by rivets. Rivets were suitable for bulletproof armour, but made hull design complicated. The Germans were the first to use partially welded hulls in the 1920s, but nobody knew about that yet. Another alternative was casting. Even the first Renault FT had cast hull elements and turrets, but this technology did not become popular for a number of reasons. The French returned to casting in the early 1930s, and even then, only to produce turrets.
Meanwhile, the use of cast parts significantly simplified hull production. The parts also turned out to be much more robust than riveted equivalents. Hotchkiss engineers from Saint-Denis (then a city north of Paris, today one of its suburbs) decided to risk using casting widely in tank manufacturing. The arms giant presented its first fighting machine in 1909, but that was an armoured car, and the company had no experience with tanks. Nevertheless, the concept proposed by Hotchkiss piqued the interest of the French army. At 30 mm or thicker, cast armour was easier to produce than riveted. In addition, the Hotchkiss company was offering a light tank, one that the French infantry was sorely in need of.