While there is much discussion about what could be done for British tanks in the 1930s, there's less about the French, despite (or perhaps because of), the immeasurably superior position of French tank forces compared to the British ones. While, key point here, still preserving the essentials of French tank doctrine, ie. a focus on methodical battle and a strict division between cavalry and infantry roles, how might you go about improving the French tank force?
My proposal, assuming control over the B1 and active changes starting from the early 1930s (and ignoring political issues with it).
-The B1 is too expensive, so drop its most complex elements (the top turret and the complex transmission), and instead have an assault gun with a longer, traversable, 75mm gun capable of both anti-tank and anti-infantry fire. Lighter, faster, more reliable, less stressed crew, arguably more firepower, but mostly cheaper.
- Since an infantry tank is inevitable (and even the reduced Char B1 is too expensive), try to have one which can be shared between the cavalry and the infantry. A somewhat larger vehicle than OTL R35/H35, with a 47mm armed, 2-man turret version for the cavalry, and a casemated version with a short 75mm gun for the infantry. Fit more radios. Add better cupolas, and maybe a machine gun that can be operated from them. (ditto for the B1)
- Build the SOMUA S35 but with a two-man turret as well, maybe even a 4 man crew.
-Don't produce anything else, even if research and prototype construction continues, and place all of the labor which went into them into above vehicles.
So hopefully this would drop the French from producing 11 tanks to 3.5 (although the AMR 33 and D1 are probably inevitably produced), the savings by concentrating on a smaller quantity of types can increase numbers, and the tanks produced can be much more versatile and much more combat capable.