There's a bit of a problem with that. Namely we don't actually know any composites-
-and we don't actually have the capacity to actually manufacture any that would be better than just plain RHA.
Especially given that we're trying to attempt something that was attempted my a much more powerful state atleast three decades later of that proposal.
The word "composite" just means a combination of parts. Like a sandwich. A sandwich is a composite food (bread + meat + cheese). So all you need to know to make a composite armor is how to make two different hard materials. Like glass and steel.
You can make glass. Glass is made in furnaces, the same kind we use to make our metal. I'm suggesting glass because the first composite armor was glass between sheets of metal, and because glass is lighter than steel while still being quite hard.
We need one of these things, plus fixed treads on the T1, in order to start winning the plains:
- More range than their autocannons.
- Immunity to 20mm ammunition.
I'd back a dedicated AT gun (longer barrel, rifling, smallish rounds) if someone proposed it, but I think improved armor would be the better choice, since that means that even in situations where an autocannon attack can't be avoided (such as at close range in the jungle or when a plane attacks) the tank will always survive.
E: Well, maybe not when a plane attacks, top armor being thin and all. I doubt making armor simply thicker would be an adequate solution unless we made a much bigger engine.