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A country gearing up for war is still limited by what it can afford. The factories have be built with material and by people, neither of which come free.
And in 1936 Germany certainly was gearing up for war, in Hitlers mind, the best defense was a offense.
You are then trying to introduce new vehicles with all their teething problems during combat. A look at German problems with the wartime introduction of both the Panther Tiger I demonstrate the problems with that policy plus you do not get the chance to store suficient advance reserves of both parts vehicles. This was not a system set up for mass production in the American style.A 1936 order for use of diesel engines would allow three or four years to build engine factories before German half tracks, Panzer III, Panzer IV and 4WD cargo trucks enter mass production. No disruption to historical vehicle production.