Good post and many good points. AFAIK, Poland is actually sitting on one of the largest copper deposits in the world, but apparently it wasn't yet discovered back then, because copper was a constant theme even in the OKW. "Discovering" this deposit in time might have helped!

In the early part of the war, would it have been possible to increase production by increasing the imports from the Soviet Union for example?

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„Solange man nicht mit dem Kopf unterm Arm rumläuft geht es doch noch!" Erwin Rommel